Expression of epithelial membrane antigen in perineurial cells and their derivatives. An immunohistochemical study with multiple markers

Perineural Infiltration: A Comprehensive Review of Diagnostic, Prognostic, and Therapeutic Implications

ABSTRACT

Perineural infiltration refers to a neoplastic cell involvement in, around, and through the nerves. It is considered as one of the neoplastic dissemination pathways. Thus, its identification is crucial to establish the prognosis of some malignant skin neoplasms, such as squamous cell carcinoma, and explains the locally aggressive behavior of cutaneous neoplasms, such as microcystic adnexal carcinoma. We have conducted a review of malignant and benign skin tumors in which perineural infiltration has been described, and we also discuss some histopathological findings that may simulate perineural infiltration.

Perineuriomatous nevi: A series of eight cases highlighting unifying pathologic features to avoid misdiagnosis

BACKGROUND

Perineuriomatous nevi are rare and diagnostically problematic. We report a series of eight perineuriomatous nevi to highlight the diagnostic features.

METHODS

Cases were retrospectively reviewed and characterized.

RESULTS

Median age was 42.5 years (range 25-64), with equal sex distribution. Lesions occurred on the arm (n = 4), trunk (n = 2), and head/neck (n = 2). Median size was 7.5 mm (range 5-12 mm). Clinical differential diagnoses included atypical nevus (3), blue nevus (1), neurofibroma (1), and dermatofibroma (1). Lesions were circumscribed, dome-shaped (5/8), and biphasic (8/8) with nested epithelioid cells and wavy spindled cells arranged in whorled fascicles in a myxocollagenous stroma. When present, junctional growth was lentiginous (4/8). No cases displayed pleomorphism or mitotic figures. The perineuriomatous component stained positively for epithelial membrane antigen (8/8 focal to diffuse) and CD34 (4/5 focal to diffuse). SOX10 and S100 protein stained all nevoid cells and in some cases a subset of intermingled spindled cells in perineuriomatous areas, where other melanocytic markers were negative. p16 protein expression was uniformly retained (3/3), and p53 negative (0/2). Nevoid cells in most lesions were positive for BRAFV600E (5/7). Ki67 was mildly elevated (~5%) in 3/3 cases.

CONCLUSIONS

Recognizing the histopathologic and immunophenotypic features in these unusual nevi helps avoid overdiagnosis.

Trigeminal hypertrophic interstitial neuropathy presenting as unilateral proptosis, ptosis, tearing, and facial neuralgia

Purpose

To show the utility of MRI and histology in diagnosing rare cases of trigeminal hypertrophic interstitial neuropathy (HIN).

Observations

A 57-year-old African-American woman presented with a 4-year history of right eye proptosis with tearing, headaches, and worsening right-sided trigeminal neuralgia symptoms and jaw pain. HIV and diabetes tests were negative and thyroid function was normal. MRI identified abnormal thickening of all trigeminal nerve divisions and proptosis secondary to right trigeminal nerve V1 division enlargement. The excised tissue contained S-100 positive Schwann cells in an onion-bulb pattern. Headaches resolved, but proptosis and mild trigeminal neuralgia remained 1 year post-surgery.

Conclusions and importance

Trigeminal HIN is very rare, but presents as chronic progressive ocular symptoms with trigeminal neuralgia. Trigeminal nerve hypertrophy is identified by MRI and confirmed histopathologically by detection of Schwann cells in an onion bulb formation.

Causes of peroneal neuropathy associated with orthopaedic leg lengthening in different canine models

Peroneal neuropathy is one of the complications of orthopaedic leg lengthening. Methods of treatment include slowing of distraction and decompression both of which may lead to additional complications. The purpose of this study was to analyse the changes in histologic peroneal nerve structure during experimental orthopaedic lengthening using various modes of manual or automatic distraction. The obtained data provide the basis for better understanding of peroneal neuropathy pathogenesis and refinement of prophylaxis and preventive treatment protocols. Four experimental models of canine leg lengthening using the Ilizarov fixator were studied: 1 (n = 10)—manual distraction—1 mm/day divided into four increments; 2 (n = 12)—automatic distraction—1 mm/day in 60 increments, 3 (n = 9) and 4 (n = 9)—increased rate of high frequency automatic distraction: 3 mm/day in 120 and 180 increments, respectively. In peroneal nerves semi-thin sections cross-sectional fascicular areas, content of adipocytes in epineurium, endoneurial vascularisation, morphometric parameters of nerve fibres were assessed by computerised analysis at the end of distraction and of consolidation periods and 30 days after fixator removal. In Groups 1–2 massive nerve fibre degeneration along with epineural vessels obliteration was revealed in two cases from 22, whereas in Groups 3–4 there were 10 from 18 (p < 0.01). Injuries of perineurium and endoneurial vessels were noted in Group 3, and long-lasting thinning of nerve fascicles in Group 4. The decrease in epineurial fat tissue was revealed in all groups, more drastic in 3. Modifications and injuries of nerve sheaths and blood vessels depending on distraction rate and frequency contribute to peroneal neuropathy. Its mechanical, circulatory and metabolic causes are discussed.

Perineurial-like Cells and EMA Expression in the Suprachoroidal Region of the Human Eye

The suprachoroidal region of the eye comprises vascular channels, melanocytes, and thin fibroblasts with elongated cytoplasm that are positioned directly adjacent to the densely collagenous sclera. Morphological similarities between these suprachoroidal fibroblasts and arachnoid cells and perineurial cells have been recognized, but whether these fibroblasts have a perineurial cell-like immunophenotype is not known. To further examine the relationship of these three cell types, we investigated the comparative expression of epithelial membrane antigen (EMA), the tight junction protein claudin-1, glucose transporter-1 (Glut-1), and CD34 in suprachoroidal fibroblasts, arachnoid of the optic nerve sheath, and perineurium of ciliary nerves in eight human eye specimens. Granular, diffuse, and cytoplasmic EMA expression was seen in suprachoroidal fibroblasts, but this was not contiguous with the similar pattern of EMA expression in adjacent perineurium and arachnoid. CD34 expression in suprachoroidal fibroblasts was also seen, similar to arachnoid and perineurium. Claudin-1 and Glut-1 were not consistently expressed in suprachoroidal fibroblasts, distinguishing them from perineurial cells in particular and suggesting that these fibroblasts do not arise directly from adjacent arachnoid or perineurium. Nonetheless, the overlapping morphology and protein expression suggest phenotypic similarities in these cells that protect and support adjacent retina, optic nerve, and peripheral nerve.

Pseudolipoblastic perineurioma: an unusual morphological variant of perineurioma that may simulate liposarcoma

Perineuriomas are rare peripheral nerve sheath tumors arising from or differentiating along the lines of normal perineurial cells. They can be divided into intraneural and soft tissue types, with the latter category including a significant number of morphological variants. Herein, we further expand their morphological spectrum to include "pseudolipoblastic" perineuriomas. These lesions occurred in the tongue of a 30-year-old man and in the triceps of a 67-year-old woman and were characterized by bland, epithelioid cells with striking intracytoplasmic vacuolization. The architecture varied, with some areas showing a striking "net-like" or "microreticular" pattern and smaller areas having a more typical spindled and whorled appearance. Clinical follow-up (5months and 52months, respectively) showed no evidence of local recurrence or metastasis. Multiple perineurial markers, including epithelial membrane antigen, claudin-1, GLUT-1, and collagen IV, were diffusely positive. Both cases were submitted in consultation out of concern that they represented high-grade liposarcomas. To the best of our knowledge, this unusual morphological variant of perineurioma has not been reported. These tumors appear to be entirely benign and should be cured with simple excision. Pseudolipoblastic perineuriomas should be distinguished from round cell and epithelioid pleomorphic liposarcomas, as well as from other tumors that may show prominent intracytoplasmic vacuolization.

Diagnostic immunohistochemistry through Rosai-coloured glasses

Over the past three decades, Immunohistochemistry has materially changed the practice of diagnostic surgical pathology. Foundational observations in this field were critical to a reasoned assessment of both the risks and opportunities that immunohistochemistry afforded the surgical pathologist, and our current practice draws heavily on those early assessments. As we collectively look to and acknowledge those who recognized the value of this technique and who helped guide its development as a companion to (not a replacement for) histomorphologic evaluation, we are drawn to those whose mastery of detail and ability to draw common patterns from seemingly unrelated phenomena helped define the diagnostic power of immunohistochemistry. The focus of this review is on one individual, Dr. Juan Rosai, whose contributions transcend the simple linkage of molecular observations to morphology, recognizing novel patterns in both form and color (the latter often the lovely shades of diaminobenzidine), seemingly viewing our diagnostic world at times through an entirely different lens. By looking at Dr. Rosai's early work in this field, reviewing a selection of his seminal observations, particularly in the Immunohistochemistry of thyroid and thymic neoplasia, revisiting how his special insight is often guided by the work of the early masters of morphology, and how his mentorship of others has helped shaped academic surgical pathology practice, perhaps we can get a glimpse through that lens.

‘Sclerosing’ Perineurioma: A Tumor Variant?

We describe two examples of soft tissue perineurioma, a hard tumor, 1.7 cm in diameter, involving the dermis and superficial subcutaneous tissue of the left thumb, and the other a massive, lobulated lesion of the pelvis. Both occurred in 49-year-old men. Both were mobile and well demarcated but unencapsulated. Their cut surfaces were white and collagenous. Microscopically, each consisted of spindle-shaped or epithelioid tumor cells in a dense stroma of haphazardly oriented collagen bundles. Spindle-shaped cells were individually distributed, whereas epithelioid cells were often arranged in cords or clusters. Cytologic atypia was conspicuous in the massive tumor, but no mitotic activity was observed. Immunostains showed diffuse reactivity for vimentin, membrane pattern staining for epithelial membrane antigen and type IV collagen, as well as patchy CD34 reactivity. Stains for S-100 protein, Leu-7, smooth muscle actin, desmin, and cytokeratin were negative. Ultrastructural studies showed perineurial cell characteristics, including slender cytoplasmic processes, numerous pinocytotic vesicles, occasional tight junctions, and discontinuous surface basement membrane. Perineuriomas featuring marked stromal sclerosis often occur in the hands of young adults, as has recently been reported; the authors considered it a clinicopathologic variant. Herein we report two sclerotic perineuriomas, one a small tumor of the thumb and the other a centrally situated, massive pelvic tumor with sclerosis and degenerative cytologic atypia. We believe that exaggerated collagen deposition in perineuriomas, occasionally associated with degenerative nuclear changes, is not a manifestation of a unique, clinically relevant tumor variant but rather a manifestation of chronicity akin to that seen in “ancient schwannoma” and ‘atypical neurofibroma.’

Tight Junction Proteins and Perineurial Cells in Neurofibromas

Cutaneous neurofibromas consist of axonal processes, Schwann cells, fibroblasts, perineurial cells, mast cells, and abundant extracellular matrix. The distribution and role of perineurial cells in neurofibromas has been uncertain, partly because there has not been a specific immunohistochemical marker for perineurial cells. In this study, tight junctions (TJs) of 16 neurofibromas from 12 patients with neurofibromatosis type 1 (NF1) were analyzed using electron microscopy, immunohistochemistry, and Western transfer analysis. Cell-cell contacts with typical ultrastructural morphology of TJs were seen between adjacent perineurial cells surrounding the small nerves and between contacting perineurial cell processes embedded in tumor stroma. Immunohistochemistry showed expression of claudin-1, claudin-3, and ZO-1 in the intercellular junctions of a subpopulation of tumor cells. Occludin was present mainly in perineurium and claudin-5 localized to the blood vessels. Double immunolabelings were used to identify the cell types expressing claudin-1. The results showed that claudin-1 positive cells were also positive for type IV collagen and epithelial membrane antigen but not for S-100 protein. This labeling pattern is consistent with perineurial cell phenotype. Using claudin-1 as a marker, our results showed that clusters of perineurial cells are distributed around the rudimentary nerves within cutaneous neurofibromas and at the periphery of some neurofibromas.

Cellular players in skeletal muscle regeneration

Skeletal muscle, a tissue endowed with remarkable endogenous regeneration potential, is still under focused experimental investigation mainly due to treatment potential for muscle trauma and muscular dystrophies. Resident satellite cells with stem cell features were enthusiastically described quite a long time ago, but activation of these cells is not yet controlled by any medical interventions. However, after thorough reports of their existence, survival, activation, and differentiation there are still many questions to be answered regarding the intimate mechanism of tissue regeneration. This review delivers an up-to-date inventory of the main known key players in skeletal muscle repair, revealed by various models of tissue injuries in mechanical trauma, toxic lesions, and muscular dystrophy. A better understanding of the spatial and temporal relationships between various cell populations, with different physical or paracrine interactions and phenotype changes induced by local or systemic signalling, might lead to a more efficient approach for future therapies.

Immunohistochemistry of soft tissue tumours - review with emphasis on 10 markers

Immunohistochemistry is an integral component in the proper analysis of soft tissue tumours, and a simple panel of six markers is useful in practical triage: CD34, desmin, epithelial membrane antigen (EMA), keratin cocktail AE1/AE3, S100 protein and alpha smooth muscle actin (SMA). These markers frequently assist in the differential diagnosis of fibroblastic, myoid, nerve sheath and perineurial cell tumours, synovial and epithelioid sarcoma and others. However, they all are multispecific, so that one has to be cognizant of their distribution in normal and neoplastic tissues. Four additional useful markers for specific tumour types are discussed here: CD31 and ERG for vascular endothelial tumours, and KIT and DOG1/Ano-1 for gastrointestinal stromal tumours (GISTs). However, hardly any marker is totally monospecific for any one type of tumour. Furthermore, variably lineage-specific markers do not usually distinguish between benign and malignant proliferations, so that this distinction has to be made on histological grounds. Immunohistochemical evaluation is most useful, efficient and cost-effective when used in the context of careful histological evaluation by an experienced pathologist, aware of all diagnostic entities and their histological spectra. Additional diagnostic steps that must be considered in difficult cases include clinicoradiological correlation and additional sampling of remaining wet tissue, if possible.

[Extraneural soft tissue perineurioma of the nose]

BACKGROUND

Perineuriomas are tumours derived from the perineurial cells of the neural sheath. Soft tissue perineuriomas are rare. Herein, we report a case of perineurioma localized to the nose.

CASE REPORT

A 24-year-old adult presented with a cutaneous nodule 1cm in diameter localized on the nose. Histologically, the tumour corresponded to a well-circumscribed fusocellular dermal proliferation organized in a storiform pattern. After surgical removal, the lesion did not recur.

COMMENTS

Extraneural soft tissue perineurioma is usually a benign nerve sheath tumour composed mainly of perineurial cells. Our case occurred in a 24-year-old Caucasian adult. The tumour generally presents as a unique cutaneous nodule corresponding histologically to a well-delineated dermal fusocellular proliferation organized in a storiform pattern that stains positive for EMA and negative for S100. The tumour is usually localized to the trunk and extremities. Location on the nose as in our patient has been rarely reported. Surgical removal of the tumour is the treatment of choice.

Neurogenic tumors of soft tissue

Neurogenic tumors are an uncommon yet important category of soft tissue tumors in children and adolescents because of their frequent association with various genetic syndromes. The heterogeneous cellular composition of the peripheral nerve and the wide metaplastic capacity of the neural crest and its derivatives generate a variety of neoplasms with neurogenic differentiation. This article reviews the clinicopathologic features and differential diagnosis of neurogenic tumors in the first two decades of life, and highlights use of selected ancillary methods for diagnosis.

Pathology of peripheral nerve sheath tumors: diagnostic overview and update on selected diagnostic problems

Peripheral nerve sheath tumors are common neoplasms, with classic identifiable features, but on occasion, they are diagnostically challenging. Although well-defined subtypes of peripheral nerve sheath tumors were described early in the history of surgical pathology, controversies regarding the classification and grading of these tumors persist. Advances in molecular biology have provided new insights into the nature of the various peripheral nerve sheath tumors, and have begun to suggest novel targeted therapeutic approaches. In this review, we discuss current concepts and problematic areas in the pathology of peripheral nerve sheath tumors. Diagnostic criteria and differential diagnosis for the major categories of nerve sheath tumors are proposed, including neurofibroma, schwannoma, and perineurioma. Diagnostically challenging variants, including plexiform, cellular and melanotic schwannomas are highlighted. A subset of these affects the childhood population, and has historically been interpreted as malignant, although current evidence and outcome data suggest they represent benign entities. The growing current literature and the author's experience with difficult to classify borderline or "hybrid tumors" are discussed and illustrated. Some of these classification gray zones occur with frequency in the gastrointestinal tract, an anatomical compartment that must always be entertained when examining these neoplasms. Other growing recent areas of interest include the heterogeneous group of pseudoneoplastic lesions involving peripheral nerve composed of mature adipose tissue and/or skeletal muscle, such as the enigmatic neuromuscular choristoma. Malignant peripheral nerve sheath tumors (MPNST) represent a diagnostically controversial group; difficulties in grading and guidelines to separate "atypical neurofibroma" from MPNST are provided. There is an increasing literature of MPNST mimics which neuropathologists must be aware of, including synovial sarcoma and ossifying fibromyxoid tumor. Finally, we discuss entities that are lacking from the section on cranial and paraspinal nerves in the current WHO classification, and that may warrant inclusion in future classifications. In summary, although the diagnosis and classification of most conventional peripheral nerve sheath tumors are relatively straightforward for the experienced observer, yet borderline and difficult-to-classify neoplasms continue to be problematic. In the current review, we attempt to provide some useful guidelines for the surgical neuropathologist to help navigate these persistent, challenging problems.

Wilms tumor-1, claudin-1 and ezrin are useful immunohistochemical markers that help to distinguish schwannoma from fibroblastic meningioma

The aim of this study is to identify immunohistochemical (IHC) markers that can reliably separate schwannoma (SCHW) and fibroblastic meningioma (FM). We selected 106 cases of intracranial SCHW (n = 56) and FM (n = 50) and constructed a tissue microarray (TMA) of core diameter of 1.0 mm from archival formalin-fixed paraffin-embedded tissue. A TMA-IHC was performed using 14 antibodies. After IHC staining, 98 cores were found suitable for evaluation. The IHC staining was scored as 0-2+ (0, negative; 1+, weak and/or focal 2+ strong and/or diffuse positive). A discriminant analysis (DA) (Wilks'Lambda test) was performed to assess the relative importance of these biomarkers in classifying the two groups FM and SCHW. It showed that WT-1 (Wilks'λ 0.085, p < 0.001), EMA (Wilks'λ 0.253, p < 0.001), S100 (Wilks'λ 0.487, p < 0.001), Claudin-1 (Wilks' λ 0.57, p < 0.001) and Ezrin (Wilks'λ 0.656, p < 0.001), SPARC (Wilks'λ 0.751, p < 0.01), NP-Y (Wilks'λ, 0.819, p < 0.001) and EGFR (Wilks'λ 0.845, p = 0.026) were some of the statistically significant markers that discriminated SCHW and FM. For sensitivity and specificity for SCHW the significant markers [Area under the curve (95% CI), p-value] by ROC analysis were WT-1 [0.990(0.000, 1.000), <0.001], S100 [0.880(0.808, 0.951), <0.001] while for diagnosing FM the most sensitive and specific markers were EMA [0.957(0.914, 1.000), <. 001], Claudin-1 [0.857(0.782, 0.932), <0.001] and ezrin [0.792(0.700,0.884),<0.001]. WT-1, Claudin-1 and Ezrin may be potentially useful immunohistochemical adjuncts to EMA and S100 that differentiate SCHW from FM.

Nerve sheath myxoma (neurothekeoma) of the gingiva, a case report and review of the literature

Nerve sheath myxoma (NSM) is a benign peripheral nerve sheath tumor that rarely occurs in the oral cavity. Among the 23 reported intraoral cases, no lesion has previously been reported on the gingiva. In this report, we describe the first gingival case of oral neurothekeoma with histopathologic and immunohistochemical characteristics. The patient, a 32 year old female presented with a slowly growing gingival mass diagnosed clinically as an epulis. The lesion was surgically excised. Histopathologically, the lesion presented as a submucosal multinodular mass composed of spindle and stellate-shaped cells with a myxoid background. Immunohistochemically, the tumor cells were sporadically positive for S-100 and NSE and negative for GFAP, EMA, SMA, CD68 and HMB45. The immunoprofile of this lesion confirmed a Schwann cell origin. The lesion was followed up for 10 months with no reports of recurrence.

Multiple hybrid granular cell tumor-perineuriomas

Hybrid peripheral nerve sheath tumors (PNSTs) are recently recognized, rarely reported entities. Very few hybrid PNSTs with elements of perineurioma have been reported. We report a case of a 47-year-old man who presented with multiple (>20) cutaneous nodules on all 4 extremities, present since childhood. The patient and his family had no history of other PNSTs, other neural-origin tumors, or genetic disorders, including neurofibromatosis. Five excised lesions are well circumscribed but unencapsulated nodular tumors composed of cytologically bland spindled cells with tapering nuclei and indistinct cytoplasm arranged in a storiform pattern in a collagenous matrix. Scattered among these cells are large granular eosinophilic cells. The spindled cells are epithelial membrane antigen-positive and S-100 protein negative. The cytoplasm of the granular cells contains abundant S-100 protein, NK1/C3, and CD68-positive granules. Sparse nerve fascicles contain neurofilament-positive axons. Each tumor also contains poorly marginated areas that histologically resemble pure granular cell tumor, and superficial biopsies of these tumors can histologically resemble pure granular cell tumors. Considering a Schwannian origin for both perineurial and granular cells can provide a logical explanation for the pathogenesis of this case. To the best of our knowledge, our case is the first report of multiple hybrid granular cell tumor-perineurioma.

Intraneural perineurioma of the radial nerve visualized by 3.0 Tesla MRI

A progressive radial neuropathy of unknown etiology despite 1.5T magnetic resonance imaging (MRI) and surgical exploration was identified as an intraneural perineurioma by a localized Tinel's sign, an enlarged radial nerve at the spiral groove by 3.0T MRI, and a fascicular biopsy. The distinction between the initial diagnoses of inflammatory, demyelinating polyneuropathy and perineurioma was made by immunohistochemistry and electron microscopy. A slowly progressing, localized mononeuropathy should include perineurioma in the differential diagnosis.

Intraneural perineurioma: a systematic review with illustrative cases

CONTEXT

Intraneural perineurioma may be confused with other "onion bulb" Schwann cell entities (localized hypertrophic neuropathy, reactive/demyelinating processes, or inherited polyneuropathies of Charcot-Marie-Tooth/Dejerine Sottas) due to similar clinical, radiologic, and histologic features. Perineurial and Schwann cells can only be differentiated by ultrastructure and immunohistochemsitry.

OBJECTIVE

To identify and summarize the clinicopathologic features of true cases of intraneural perineurioma from the English language literature.

DATA SOURCES

A systematic review was performed on definitive intraneural perineuriomas identified through Medline. Baylor College of Medicine-affiliated hospitals' anatomic pathology databases yielded 2 illustrative intraneural perineurioma cases.

STUDY SELECTION

Intraneural perineurioma inclusion criteria consisted of characteristic histology and confirmation of perineurial cell lineage by either immunohistochemistry (epithelial membrane antigen positive, S100 protein negative) and/or ultrastructural analysis (thin cytoplasmic processes with an incomplete basal lamina, poorly formed tight junctions, and pinocytotic vesicles).

DATA EXTRACTION

Clinicopathologic data were extracted from all identified articles, with subsequent statistical analysis of the following parameters: age, sex, race, tumor location, tumor size, duration of symptoms prior to diagnosis, treatment modalities and outcomes measures, follow-up assessment for tumor recurrence and metastasis, clinical features (history of trauma, motor/sensory abnormalities, clinical/family history), and diagnostic workup (routine histology, immunohistochemistry, ultrastructural analysis, and molecular/cytogenetic characteristics).

CONCLUSIONS

Intraneural perineurioma is a neoplastic proliferation of perineurial cells with unique immunohistochemistry and ultrastructural features, and it is distinct from other onion bulb Schwann cell-derived entities. Despite harboring molecular abnormalities of the long arm of chromosome 22, intraneural perineurioma has not been associated with neurofibromatosis. Intraneural perineurioma is a benign peripheral nerve sheath tumor that does not recur or metastasize.

Novel fibroblastic onion bulbs in a demyelinating avian peripheral neuropathy produced by riboflavin deficiency

The finding of novel fibroblastic onion bulb-like structures in peripheral nerves is reported for the first time in avian riboflavin deficiency. Day old broiler meat chickens were fed a riboflavin deficient diet (1.8 mg/kg) and were killed on postnatal days 6, 11, 16, 21 and 31, whereas control chickens were fed a conventional diet containing 5.0 mg/kg riboflavin. The fibroblastic onion bulb-like structures were found in sciatic and brachial nerves from day 11 onwards and consisted of long cytoplasmic processes of hypertrophied fibroblasts surrounding demyelinated, remyelinated and normally myelinated axons. The fibroblast cytoplasmic processes often enveloped more than one nerve fibre to produce a unique compound-like onion bulb structure. These onion bulb-like structures occurred early in the course of segmental demyelination at the same time as tomacula formation and became increasingly more prominent in the later stages of demyelination and remyelination. The molecular basis of formation of these unique structures requires further study as to the basis of the attraction of the fibroblast processes to nerve fibres associated with myelinating Schwann cells. The model may also be useful in investigating the role of endoneurial fibroblasts in endoneurial fibrosis as the early fibroblastic response in the onion bulbs is distinct from the more usual fibroblastic deposition of collagen in end-stage peripheral nerve disease.

Mucosal benign epithelioid nerve sheath tumors

Mucosal nerve sheath tumors have been well described in the gastrointestinal tract and other mucosal sites. In a series of mucosal biopsies, we have encountered a distinct subset of mucosal peripheral nerve sheath tumors characterized by small epithelioid cells and a benign clinical course. Such epithelioid nerve sheath tumors have been observed as a component of a larger study of colorectal "schwannomas," but herein we describe them in detail. A series of 7 of these lesions detected on mucosal biopsies (6 colonic, 1 bladder) was received by a single large institution in consultation material. The histologic and clinicopathologic features of the cases were reviewed. The mean age at presentation was 58.6 years with a slight female predominance (4 females, 3 males). Five of the colonic lesions were from the left colon and one from the right colon. The bladder biopsy was from the bladder neck. All of the colonic lesions were discovered as small (0.2-1.0 cm) polyps during the time of colonoscopy (3 at the time of routine screening, 2 for the workup of occult blood in the stool). The bladder neck mass was seen on bladder ultrasound after the patient presented with vaginal bleeding. None of the patients had a known history of neurofibromatosis. Histologically, the lesions showed an infiltrative growth pattern and were composed of spindled to predominantly epithelioid cells arranged in nests and whorls. The epicenters of the lesions were located in the lamina propria and extended to the superficial submucosa. The proliferating cells had uniform round to oval nuclei with frequent intranuclear pseudoinclusions and eosinophilic fibrillary cytoplasm. No mitoses were seen. All lesions expressed diffuse S-100 protein, and 3 of 5 lesions stained showed CD34 labeling in supporting cells. All were negative for CD117. All 5 lesions tested were negative for calretenin, while SM31 showed no intralesional neuraxons. One lesion was stained for epithelial membrane antigen and was negative. One lesion was associated with superficial mucosal erosion, and 1 had an inflammatory infiltrate predominantly composed of eosinophils. On follow-up of 5 patients, none has had any symptoms or recurrence of disease. Mucosal epithelioid nerve sheath tumors are a rare entity characterized by prominent epithelioid round to oval cells with an infiltrative growth pattern. These lesions are often discovered incidentally and have a benign clinical course.

Low-grade malignant perineurioma (perineurial sarcoma) of soft tissue: a potential diagnostic pitfall on fine needle aspiration

A case of low-grade malignant perineurioma presenting as a mass in the thigh is described. The patient was a 76-year-old woman with an enlarging painful mass on her right lateral thigh over the past 2 months. Thorough clinical and radiological studies did not reveal any evidence of tumor elsewhere. The patient underwent fine needle aspiration of the mass, which revealed pleomorphic spindle cells in small clusters or dispersed as single cells within myxoid stroma, cytologically consistent with a high-grade sarcoma. At surgery, the tumor was found to be entirely confined within the muscle. Grossly, the tumor measured 6.5 cm in greatest diameter and showed a gray-white fleshy cut surface that was well circumscribed but unencapsulated. Histologic examination showed a highly cellular spindle cell proliferation embedded within myxoid stroma. The tumor cells showed mild to moderate nuclear pleomorphism with minimal mitotic activity. No evidence of hemorrhage or necrosis was noted. The tumor irregularly invaded the surrounding skeletal muscle. Immunohistochemical studies showed weak membranous positivity for epithelial membrane antigen and focal cytoplasmic positivity for CD34; stains for smooth muscle actin, cytokeratin AE1/AE3, desmin, CD56, H-caldesmon, calponin, and S-100 protein were negative. Electron microscopy showed cells with thin, elongated cytoplasmic processes extending along connective tissue in a parallel, onion-like arrangement and prominent subplasmalemmal pinocytotic activity. The marked pleomorphism displayed on fine needle aspiration observed in this case can lead to a mistaken diagnosis of high-grade sarcoma resulting in unnecessarily aggressive management.

Hybrid peripheral nerve sheath tumors: Schwannoma-perineurioma and neurofibroma-perineurioma. A report of three cases in extradigital locations

We present three cases of subcutaneous tumors with hybrid features of schwannoma-perineurioma (one case) and neurofibroma-perineurioma (two cases), which occurred in two women aged 50 and 52 years and one man aged 52. Locations included the scapular area, skin overlying breast and knee area. The tumors were 1.5, 4 and 5 cm in largest diameter. None of the patients had signs of neurofibromatosis. All tumors were surgically removed, and patients remained disease-free for 1 to 4 years. The classification of the lesion into schwannoma-perineurioma and neurofibroma-perineurioma rested on histopathological and immunohistochemical findings. An ultrastructural study was performed in one case of neurofibroma-perineurioma. All cases were studied for mutation of the NF2 gene, and in one case (neurofibroma-perineurioma) a point mutation was detected in exon 15 of the gene.

Lucien J. Rubinstein: enduring contributions to neuro-oncology

Dr. Lucien Rubinstein is best remembered for his significant contributions to the field of neuropathology, particularly in the classification of nervous system tumors. His accomplishments in basic neuro-oncology and in the formulation of diagnostic principles reflected a unique talent for synthesizing fundamental clinicopathological concepts based on skillful diagnostic investigation and a thorough understanding of neurobiology. Dr. Rubinstein was the leader in the establishment of cell cultures from central nervous system (CNS) tumors. He meticulously analyzed both light and electron microscopic features of CNS tumors, recorded his findings, and patiently drew sketches to be shared generously with his colleagues and students. As a pioneer in neuropathology, in his work Dr. Rubinstein set the foundation for many enduring concepts in neurosurgery, neuro-oncology, neurology, and basic tumor biology.

Intraneural perineurioma involving the ulnar nerve

Intraneural perineurioma is a rare peripheral nerve sheath tumor consisting of intraneural proliferation of neoplastic perineurial cells. Clinical and pathological findings of a perineurioma involving the ulnar nerve is presented. A 7-year-old girl presented with a 2 year history of weakness and atrophy of the right hand muscles. Physical examination and imaging study revealed a pea-sized tumor in the ulnar side of the right forearm. At surgery, a fusiform swelling of the ulnar nerve was found and an excisional biopsy of the lesion was performed. Light microscopy revealed numerous whorls consisting of concentric layers of spindle cells encircling the nerve fibers. The proliferating cells were immunoreactive for vimentin, epithelial membrane antigen and glucose transporter protein 1 (Glut1), but negative for S-100 protein and CD34. Ultrastructural examination revealed features of perineurial cell differentiation. The current study suggests that Glut1 is a useful marker of intraneural perineurioma.

Benign Fibroblastic Polyps of the Colon

Mesenchymal proliferations presenting as mucosal polyps are relatively uncommon and are represented by gastrointestinal stromal tumors, smooth muscle and neural tumors, and inflammatory fibroid polyps. In this report, we describe the clinicopathologic features of a distinctive type of mucosal polyp composed of cytologically bland spindled cells with fibroblastic features. Fourteen cases with histologic features of"fibroblastic polyps" were identified from our case files from January 2000 to December 2003. The clinical and endoscopic findings were reviewed. Immunohistochemistry using a panel of antibodies (vimentin, smooth muscle actin, desmin, CD31, CD34, Bcl-2, c-Kit, S-100, and epithelial membrane antigen) was performed in all cases, and electron microscopy was performed in two cases. The lesions were solitary in all cases and not associated with an identifiable polyposis syndrome. Associated adenomata and/or hyperplastic polyps at different sites were present in 10 cases and hyperplastic polyps were seen in close association in 3 cases. These polyps were characterized by a monomorphic spindle cell proliferation in the lamina propria, without necrosis or mitotic activity. The lesions were intimately associated with the muscularis mucosae and resulted in wide separation and disorganization of the colonic crypts. Immunohistochemical analysis revealed strong and diffuse positivity for vimentin only. Weak and focal reactivity was noted in 2 cases for CD34 and smooth muscle actin, while staining for other antibodies was negative. Electron microscopy revealed sparse cytoplasmic organelles and many intermediate filaments. The histology and ultrastructural and immunohistochemical findings are suggestive of fibroblastic differentiation of these spindle cells. In summary, these lesions represent a distinctive type of colonic mucosal polyp that should be distinguished from other stromal polyps of the gastrointestinal tract.

Dermatofibrosarcoma protuberans with EMa+ cells. Report of a case suggesting perineurial cell differentiation

A case of dermatofibrosarcoma protuberans (DFSP) with epithelial membrane antigen (EMA)-positive cells is described. The tumor was excised from the left groin of a 28-year-old woman. It showed characteristic histologic features of DFSP with typical diffuse immunohistochemical positivity for CD34. Moreover, scattered neoplastic cells expressed EMA, suggesting perineural cell differentiation. Ultrastructural study found perineurial cell features, such as thin long bipolar cytoplasmic processes, pinocytotic vesicles, fragments of external lamina and/or external lamina-like material, attachment plaques, and desmosome-like junctions. This observation, together with previous immunohistochemical findings of EMA-positive cells in a subset of DFSPs, strongly suggests perineurial cell differentiation in these tumors. DFSP should be included in the differential diagnosis of EMA-positive spindle cell lesions of superficial soft tissue and skin.

Immunohistochemical demonstration of EMA/Glut1-positive perineurial cells and CD34-positive fibroblastic cells in peripheral nerve sheath tumors

To clarify the cellular composition of various peripheral nerve tumorous lesions (traumatic neuroma, 5 cases; schwannoma, 10 cases; neurofibroma, 14 cases; perineurioma, 3 cases; conventional malignant peripheral nerve sheath tumor (MPNST), 7 cases; perineurial MPNST, 4 cases), expression of several markers specific to nerve sheath cells, including glucose transporter protein 1 (Glut1) and CD34, were immunohistochemically investigated with highly sensitive detection methods. In normal nerves and neuromas, perineuriums were positive for Glut1 as well as for epithelial membrane antigen (EMA), and there were some CD34-positive fibroblast-like cells in the endoneurium. Schwannomas consisted principally of S-100 protein-positive Schwann cells, whereas a few CD34-positive fibroblastic cells were present in Antoni B areas. Neurofibromas and conventional MPNST exhibited a mixed proliferation of S-100 protein-, EMA/Glut1-, and CD34-positive cells, indicating a heterogeneous composition of the constituents. The catalyzed signal amplification (CSA) system demonstrated more numerous EMA-positive perineurial cells in neurofibromas than did the ENVISION+ method. Perineurial cell tumors (benign and malignant) were composed of EMA/Glut1-positive and S-100 protein-negative tumor cells. The present study confirmed the characteristic cellular composition to each nerve sheath tumor immunohistochemically and showed the usefulness of the nerve sheath cell markers. Glut1 as well as EMA are specific to perineurial cells, and CD34 seems to be immunoreactive to endoneurial fibroblasts.

Expression of claudin-1, a recently described tight junction-associated protein, distinguishes soft tissue perineurioma from potential mimics

Perineuriomas are rare benign soft tissue tumors having an immunophenotype paralleling the normal perineurial cell [S-100 protein negative and epithelial membrane antigen (EMA) positive]. Because EMA expression in perineuriomas may be focal and/or faint, there is continued interest in the development of new markers of perineurial differentiation. Perineurial cells differ from almost all other mesenchymal cell types by virtue of their formation of tight junctions. In the course of evaluating a group of novel tight junction-associated proteins, we noted high levels of expression of claudin-1 by normal perineurial cells and have systematically extended these observations to perineuriomas. Twelve EMA-positive/S-100-negative perineuriomas were retrieved from our consultation archives and compared with 39 tumors in the differential diagnosis of perineurioma (seven dermatofibrosarcoma protuberans, eight low-grade fibromyxoid sarcomas, three desmoplastic fibroblastomas, seven fibromatoses, nine neurofibromas, and five schwannomas). All cases were immunostained for claudin-1 using standard avidin-biotin technique. Cases were scored as 3+ (>50% positive cells), 2+ (25-50% positive cells), and 1+ (5-24% positive cells). In all cases positive internal controls in the form of epithelium, normal perineurium, or endothelial cells were present. Positive staining for claudin-1 was visualized in a distinctly particulate pattern along the cell membrane. Cytoplasmic staining was infrequent and was not scored as positive. Claudin-1 expression was present in 11 of 12 (92%) perineuriomas studied (seven at 3+, three at 2+, and one at 1+). In all but two cases, the degree of claudin expression was equal to or greater than the corresponding EMA immunostain. Claudin-1 expression was not noted in any cases of dermatofibrosarcoma protuberans, low-grade fibromyxoid sarcoma, desmoplastic fibroblastoma, or fibromatosis. Six of nine cases of neurofibroma contained a significant number of claudin-1-positive cells that were thought to be perineurial in origin, based on the staining of long, delicate cytoplasmic processes. One of four schwannomas contained a subpopulation of perivascular, dendritic, claudin-1-positive cells of presumed perineurial lineage. This is the first study to document expression of claudin-1 in perineurial cells and suggests a role for claudin-1 immunohistochemistry in the diagnosis of perineuriomas. Although claudin-1 should not replace EMA in the diagnosis of perineurioma, we think that it may play a valuable adjunctive role in difficult cases. In particular, claudin-1 is often a more robust marker than EMA in a given perineurioma. Claudin-1 is not expressed within the lesional cells of the mesenchymal tumors that enter into the differential diagnosis of perineurioma.

Atypical cells in human cutaneous re-excision scars for melanoma express p75NGFR, C56/N-CAM and GAP-43: evidence of early Schwann cell differentiation

BACKGROUND

A common problem in the routine examination of melanoma re-excision scars occurs when a few or rare mildly atypical cells are present within the scar, raising the question of residual disease. Little is known about the derivation of these cells. Because the normal cutaneous wound-healing process is reparative, we hypothesized that these atypical cells may be reactive proliferating Schwann cell precursors.

METHODS

The expression of the Schwann cell differentiation markers p75NGFR, CD56/N-CAM and GAP-43 was examined by immunohistochemistry in scars of wide local re-excisions for melanoma and non-melanoma tumors. Expression of S100, gp100 (with HMB45) and MART1 was also analyzed by immunohistochemistry.

RESULTS

All melanoma and non-melanoma re-excision specimens contained mildly atypical, spindled or epithelioid cells within the scar. They varied in number from case to case and expressed S100, p75NGFR, CD56/N-CAM or GAP-43 but not gp100 (with HMB45) or MART1. Rare epithelioid non-melanoma cells within the superficial dermis expressed MART-1.

CONCLUSIONS

Atypical cells are present in re-excision scars from melanoma and non-melanoma cases. They demonstrate early Schwann cell differentiation and appear to proliferate during the scarring process. The use of anti-MART-1 alone in the examination of melanoma re-excisions specimens may be inadequate as it may label rare, superficially located, non-melanoma cells within the scar.

Perineurial cell differentiation in neurofibromas. Report of eight cases including a case with composite perineurioma-neurofibroma features

Among 99 cases of neurofibroma (NF), eight tumors (8%) contained epithelial membrane antigen (EMA)-positive perineurial cells inside the lesions. These cells were numerous and represented a significant part of the tumor cell population. In case 7, EMA-positive cells represented approximately half of the tumor. These patients' ages ranged from 23 to 73 years (average 51 years). Six patients were females and two were males. Neurofibromatosis type 1 was present in one case. The histological types of neurofibromas with EMA-positive cells were as follows: cutaneous, well-circumscribed, localized type in four cases; cutaneous diffuse type in one case; subcutaneous, well-circumscribed type in two cases; and subcutaneous plexiform type in one case. Perineurial cell differentiation was suspected by examining routinely stained sections in four cases; it was unsuspected in four cases. The perineurial cells were arranged in a pattern similar to that of "pure" perineurioma. They possessed thin bipolar processes and were arranged in laminar fascicles and whorls. In cellular areas, the cytoplasm was more eosinophilic and cell borders were poorly visible. In contrast, when the stroma was myxoid, it accentuated the shape of individual cells. As these morphological features of perineurial cell differentiation in NF are not entirely specific, EMA staining is recommended to prove the perineurial cell differentiation in neurofibromas. An additional immunohistochemical result of this study is the presence of numerous CD34-positive cells in all neurofibromas, which is similar to previous studies.

Intraneural perineurioma of the common peroneal nerve. Case report and review of the literature

Intraneural perineurioma, or localized hypertrophic mononeuropathy (LHM), is a focal lesion that produces a slowly progressive mononeuropathy in a peripheral nerve. The authors describe the clinical presentation, magnetic resonance (MR) neurography characteristics, and pathological characteristics of a perineurioma involving the peroneal nerve. Although there has been much debate surrounding the cause of this lesion, a literature review supports the argument that this is a neoplastic lesion, best referred to as intraneural perineurioma. Surgical management includes excision to prevent progression of palsy and placement of a nerve graft if clinically indicated. A 28-year-old woman presented with a 2-year history of progressive painless right peroneal nerve palsy. Magnetic resonance neurography revealed a right common peroneal nerve mass. At surgery, the mass was easily excised, leaving significant nerve fascicles intact. Intraoperative biopsy was not performed nor was a nerve graft placed. Pathological investigation demonstrated onion bulb-shaped whorls consistent with the appearance of intraneural perineurioma; immunochemical analysis confirmed the diagnosis. A review of the literature supports the argument that perineurioma, or LHM, is a neoplastic process, making "intraneural perineurioma" the most appropriate name. The authors also demonstrate the utility of MR neurography in the identification isolated nerve tumors and review the surgical management of this lesion.

Development of Meissner-like and Pacinian sensory corpuscles in the mouse demonstrated with specific markers for corpuscular constituents

The development of Meissner-like and Pacinian corpuscles was studied in mice [from postnatal day (Pd) 0 to 42] by using immunohistochemistry for specific corpuscular constituents. The battery of antigens investigated included PGP 9.5 protein and neurofilaments, as markers for the central axon; S100 protein, vimentin, and p75(LNGFR) protein, to show Schwann-related cells; and epithelial membrane antigen to identify perineurial-related cells. In Meissner-like corpuscles immunoreactivity (IR) for neuronal markers was found by Pd7 and later. The lamellar cells of these corpuscles expressed first S100 protein IR (Pd7 to Pd42), then vimentin IR (Pd12 to Pd42), and transitory p75(LNGFR) IR (Pd7 to Pd19-20). Vimentin IR, but not epithelial membrane antigen, was detected in the capsule-like cells of the Meissner-like corpuscles. On the other hand, the density of Meissner-like corpuscles progressively increased from Pd0 to Pd19-20. Pacinian corpuscles were identified by Pd7. From this time to Pd42 the central axon showed IR for neuronal markers, and the inner core cells were immunoreactive for S100 protein. Moreover, vimentin IR was detected in the inner core cells by Pd19 and later. Unexpectedly, the central axons displayed S100 protein IR (from Pd7 to P28), while p75(LNGFR) protein IR or epithelial membrane antigen IR were never detected. Taken together, and based on the expression of the assessed antigens alone, the present results suggest that the Meissner-like and the Pacinian corpuscles in mice become mature around Pd19-Pd28 and Pd20, respectively. Furthermore, these results provide a baseline timetable for future studies in the normal or altered development of sensory corpuscles in mice since specific sensory corpuscles are functionally associated with different subtypes of sensory neurons the development of which is selectively disturbed in genetically manipulated mice.

Immunohistochemistry in diagnostic dermatopathology

This article briefly reviews many immunohistochemical stains that have been in use for years, emphasizing their diagnostic use and potential pitfalls. Several newer immunostains are described in a more comprehensive fashion, including brief summaries from recently published studies.

Perineurial malignant peripheral nerve sheath tumor (MPNST): a clinicopathologic, immunohistochemical, and ultrastructural study of seven cases

Most malignant peripheral nerve sheath tumors (MPNST) are schwannian in nature. The pathologic features of MPNST with perineurial cell differentiation remain to be characterized. To determine the clinicopathologic, immunohistochemical, and ultrastructural characteristics of perineurial MPNST, 121 MPNST from the Mayo Clinic Tissue Registry were examined. Of these 23 spindle cell tumors with long processes disposed in whorls or storiform patterns, features typical of perineurioma, were studied. On the basis of immunohistochemistry (epithelial membrane antigen+/S-100-), 5 perineurial MPNST were identified among 23 tumors selected. These and two previously characterized perineurial MPNST are the subject of this study. None of seven tumors was associated with NF-1. Patients included five males and two females ranging in age from 11 to 83 years (mean, 45.7 years). The tumors measured 1.5 to 30 cm (mean, 9.1 cm) and arose in the extremities (two), trunk (two), face (one), mediastinum (one), and retroperitoneum (one). Only one tumor was nerve associated (phrenic nerve). All tumors were surgically removed. No encapsulation or neurofibroma components were noted. Necrosis was seen in three lesions. Four tumors were classified as high-grade malignant and three as low grade. Mitotic indices varied from 1 to 85/10 high-power fields (median, 16). Immunoreactivities included epithelial membrane antigen (100%), vimentin (100%), Leu-7 (57%), and CD34 (14%). Stains for S-100 protein, muscle markers, and cytokeratin were nonreactive. Ultrastructurally, perineurial-like cells were noted in three tumors and cells intermediate between perineurial and Schwann cells in one. Four tumors recurred and two metastasized; no deaths of disease were noted at follow-ups of 28 to 98 months (mean, 66.9). In conclusion, 4% of MPNST show perineurial cell differentiation. An NF-1 association has yet to be described. Nerve involvement is infrequent. Their immunophenotype (epithelial membrane antigen+/S-100-) frequently indicates ultrastructural perineurial differentiation. The prognosis of perineural MPNST appears to be more favorable than that of conventional MPNST.

Sclerosing perineurioma: a clinicopathologic study of 19 cases of a distinctive soft tissue lesion with a predilection for the fingers and palms of young adults

This report describes 19 cases of a distinctive sclerosing perineurial tumor of the hands. Fourteen patients were male and five were female (age range 9-55 years; median age 24.5 years). The process typically presented as a painless mass and was present from 6 months to 40 years before resection. Sites of involvement were the thumb (n = 6); index (n = 3), middle (n = 4), and ring (n = 4) fingers; and the palm (n = 2). The lesions were generally well marginated but nonencapsulated. They had a firm, fibrous consistency and ranged in size from 0.7 to 3.3 cm in maximum dimension. Microscopic examination showed abundant dense collagen and variable numbers of small, epithelioid, and spindled cells exhibiting corded, trabecular, and whorled (onion bulblike) growth patterns. Immunoreactivity was present for epithelial membrane antigen (15 of 15); a cytokeratin cocktail containing AE1, AE3, and CK1 (four of 14); CAM 5.2 (one of 12); vimentin (12 of 12); muscle-specific actin (nine of 14); alpha-smooth muscle actin (six of 14); collagen IV (six of six); laminin (five of six); and CD99 (three of five). Ultrastructural features consistent with perineurial cells were noted. All of the lesions were locally excised. Follow-up was obtained for seven patients, with mean and median follow-up intervals of 12 years 7 months and 10 years 6 months, respectively. None of the lesions have recurred. This study advances the morphologic spectrum of perineurioma, a rare tumor of nerve sheath derivation. Familiarity with this distinctive subtype should help to avoid confusion with other processes, including a fibroma of tendon sheath, the sclerotic fibroma associated with Cowden's disease, an epithelioid neurofibroma, a late stage of tenosynovial giant cell tumor, and sclerosing adnexal tumors.

Perineurial cell tumor (perineurioma) with granular cells

A form of benign cutaneous tumor with perineurioma findings and with the presence of associated granular cells is described. The two cases studied consisted of whorls made up of a high number of circumferentially arranged flattened cells, with perineurial characteristics, including bipolar cell processes, pinocytotic vesicles, a basal lamina, a positive immunoreactivity for EMA, and absence of immunostaining for S-100 protein. The granular cells, enclosed within the whorls, contained densely packed vesicles, particles with an apparently solid core, as well as membrane-limited vacuoles with disintegrating cellular organelles and electron-dense amorphous material. While failing to demonstrate any immunoreactivity for EMA, the granular cells showed positivity for S-100 protein, which supports their Schwann-cell origin. Due to its morphological and immunohistochemical characteristics, this peculiar form of tumor can be considered as a perineurioma with perineurial cell whorls and granular cell changes occurring in associated Schwann cells at the center of the whorls.

Study of human cutaneous sensory corpuscles using double immunolabelling and confocal laser scanning microscopy

BACKGROUND

The main constituents of sensory corpuscles, i.e., the central axon, the periaxonic Schwann-related, cells, and the perineurial-related cells, can be identified light microscopically by simple immunohistochemistry using specific antibodies. This paper demonstrates the usefulness of double immunolabelling for light and confocal laser-scanning microscopy (CLSM) in the study of human cutaneous sensory corpuscles.

MATERIALS AND METHODS

Antibodies directed against neurofilament proteins (NFPs) and S-100 protein were used to label the central axon and the lamellar cells of Meissner corpuscles or the inner-core lamellae of digital cutaneous Pacinian corpuscles, respectively. Samples were obtained from subjects with normal sensitivity and from patients with paresthesia or absence of clinical sensitivity. Single and double immunolabelling was performed, and the sections were studied by light or CLSM microscopy.

RESULTS

Double immunolabelling was effective for simultaneous observation of the central axon (NFP-positive) and periaxonic Schwann-related (S-100 protein-positive) cells in sensory corpuscles from normal human digital skin. The images that were obtained with both methods were comparable, but the axonic profiles were sharper with diaminobenzidine (DAB) used as a chromogen rather than with Texas-red used as a fluorochrome. Nevertheless, the ability to manipulate the focal plane by using CLSM permits one to better analyze the intracorpuscular relationships of the axon. Double immunolabelling in sensory corpuscles from the skin of patients with nerve compression showed the presence of a central axon in the corpuscles, whereas it was absent in the sensory corpuscles of clinically denervated skin.

CONCLUSIONS

Double immunolabelling is a useful method with which to analyze simultaneously two of the corpuscular constituents, and it may be used in the study of denervated and reinnervated sensory corpuscles.

Immunohistochemistry of human cutaneous Meissner and pacinian corpuscles

This paper reviews the immunohistochemical characteristics of two kinds of human cutaneous sensory nerve formations (SNFs), the Meissner and Pacinian corpuscles. In both kinds of SNF the central axon might be easily identifiable because it displays immunoreactivity (IR) for the neuroendocrine markers neuron-specific enolase and protein gene product 9.5, as well as for neuron-specific intermediate filament proteins, i.e., neurofilaments. Other intermediate filament proteins such as vimentin are localized in the lamellar cells of Meissner corpuscles, and in the inner core, outer core and capsule of Pacinian corpuscles. However, they lack cytokeratins or glial fibrillary acidic protein IR. On the other hand, and in agreement with ultrastructural data, IR for basement membrane constituents laminin and type IV collagen is found underlying all SNF constituents, with the exception of the axon. One of the mechanisms involved in the maintenance of intracellular calcium ions (Ca2+) homeostasis is the calcium binding proteins. Ca2+ play a key role in the mechanoelectric transduction and have been localized in SNFs. In this way IR for the Ca(2+)-binding proteins calbindin D28K, parvalbumin and calretinin, is present and colocalized in both Meissner and Pacinian corpuscles; furthermore, S-100 protein is exclusively localized in the lamellar cells and the inner core. On the other hand, the skin is a main source of neurotrophins for a subset of neural crest sensory neurons, some of which end forming SNF. These factors are conveyed via retrograde axonal transport from the skin to the cell body of the responsive neurons. Interestingly, Meissner and Pacinian corpuscles also display IR for the pan-neurotrophin low-affinity receptor (p75), and for the trkA receptor protein, a basic constituent of the high-affinity receptor for some neurotrophins. Moreover, they express IR for the epidermal growth factor receptor. Finally, other antigens not proper to the cells forming human cutaneous SNF, such as the epithelial membrane antigen and the leucocytary antigen-7, have also been detected.

Ultrastructural heterogeneity of acquired intradermal melanocytic nevus cells

The present ultrastructural evaluation of 12 acquired intradermal melanocytic nevi revealed that in contrast to the nested epithelioid melanocytic nevus cells of the upper dermis, the spindle nevus cells of the deep dermis showed perineurial differentiation, exhibiting a spindly configuration characterized by a melanosome-free cytoplasm that showed extremely slender bipolar contour and contained abundant intermediate filaments, a decreased number of cytoplasmic organelles, and, significantly, a fair number of plasmalemmal pinocytotic vesicles. The nevic corpuscles were found to consist of laminated slender cytoplasm showing subcellular conformation similar to that of the spindle nevus cells. By immunohistochemistry, many spindle nevus cells and nevic corpuscles were immunoreactive for nerve growth factor receptor. All the nevus cells were immunoreactive for vimentin and S-100 protein, and negative for protein gene product 9.5, epithelial membrane antigen, Leu-7, and myelin basic protein. Characteristically, protein gene product 9.5 immunohistochemistry revealed numerous immunoreactive axons intermingled with the spindle nevus cells in the deep portion. All the PGP9.5-immunoreactive axons were observed by immunoelectron microscope to be unmyelinated and always ensheathed by a thin cytoplasmic process of Schwann cells but not nevus cells. These findings indicate that differentiation plasticity exists in the various nevus cells, with the epithelioid nevus cells and the spindle nevus cells displaying more ultrastructural and immunophenotypical characteristics of melanocyte and perineurial cells, respectively, suggesting that a pluripotential cell of neural crest origin accounts for the histogenesis of this lesion.

Ultrastructural study of a perineurioma with ribosome-lamella complexes

The participation of the perineurial cell in peripheral nerve tumors is the subject of much debate. The case of a 75-year-old female with a soft tissue tumor on her left shoulder is presented. The tumor had histological, ultrastructural, and immunohistochemical characteristics of a pure perineurial cell neoplasm. Ultrastructurally, distinctive ribosome-lamella complexes were found in the cytoplasm of the perineurial cells. This may be the first time that these structures have been described in perineurioma.

Perineurioma (storiform perineurial fibroma): clinico-pathological analysis of four cases

Four cases of perineurioma (storiform perineurial fibroma) arising in the dermis, subcutis, or deep soft tissue have been studied. Two patients were female and two were male with ages ranging from 19 to 45 years. One lesion each arose on the chest wall, shoulder, neck, and elbow. Follow-up information in three patients revealed no recurrence. Histologically, the neoplasms were circumscribed but non-encapsulated lesions and were composed of spindle cells with elongated bipolar cytoplasmic processes, inconspicuous fusiform nuclei and well-defined palely eosinophilic cytoplasm. These cells were arranged in whorls or lamellar-like structures and often demonstrated a storiform growth pattern. In areas, the tumour cells appeared larger with more rounded nuclei. Immunohistochemically, most of the tumour cells stained positive for epithelial membrane antigen and vimentin, but failed to stain for S-100 protein, neurofilament, desmoplakin, and CD34. Ultrastructurally, two cases showed fusiform tumour cells with long, thin cell processes separated by abundant collagen bundles. Tumour cells were covered by discontinuous external lamina, showed many pinocytic vesicles and occasionally desmosome-like structures. The morphology and EMA immunopositivity of perineurioma are similar to meningioma, especially to cutaneous meningioma type II. We believe that perineurioma and meningioma are closely related, but morphologically distinguishable, neoplasms.

Fine structural and immunohistochemical identification of perineurial cells connecting proximal and distal stumps of transected peripheral nerves at early stages of regeneration in silicone tubes

Perineurial cells are specialized connective tissue cells that form a barrier between endoneurium and epineurium in normal nerves. In the present study, the formation of the perineurium after transection of rat sciatic nerves was investigated. The cord bridging the gap between proximal and distal stumps through silicone tubes was studied 3, 7, 12, 18, and 21 days after surgery using electron microscopy and antibodies against epithelial membrane antigen (EMA), a marker for perineurial cells that has thus far not been applied to the study of differentiating cells in nerve tubulation systems. Initially, a thin cord consisting of fibrin bridged the gap between the stumps. At 7 days, longitudinal cells had migrated from both stumps toward the center of the tubes on the surface of the fibrin cord. These cells were immunoreactive with anti-EMA. At 12 days, ultrastructural features of perineurial cells (desmosomes, tight junctions, actin filaments with dense bodies, tonofilaments) were prominent in these cells. Subsequently, the gap was bridged through the perineurial tube by endothelial cells, pericytes, fibroblasts, Schwann cells, and axons. At 21 days, a single large nerve fascicle ensheathed by a mature perineurium was found between the stumps. Thus, the first cells to connect proximal and distal stumps in the investigated nerve regeneration silicon chamber system are perineurial cells. Through the tube formed by these cells, blood vessels and nerve fibers bridge the gap. Therefore, establishment of a perineurial connection between nerve stumps appears to be important in the sequence of events during nerve regeneration.

Lectin histochemistry of normal and neoplastic peripheral nerve sheath. 2. Lectin binding patterns of schwannoma and neurofibroma

Lectin binding patterns of 31 schwannomas and 6 neurofibromas were examined using 12 lectins, and the results were compared with those of normal peripheral nerves. Tumors obtained from 10 cases of neurofibromatosis and 4 recurrent schwannomas were included. Changes of glycoconjugates were observed in association with a neoplastic transformation of Schwann cells; Arachis hypogaea (PNA) staining after neuraminidase treatment seen in normal Schwann cells was reduced in schwannoma of Antoni type A, and bindings with Glycine max (SBA) and Helix pomatia (HPA) after sialic acid removal, which were not seen in normal Schwann cells, appeared in schwannoma cells. Intensities of staining of tumor cells with each lectin were higher in Antoni type B than those in Antoni type A. No differences in lectin binding patterns were observed between schwannomas in patients with neurofibromatosis or recurrent schwannomas and ordinary, primary schwannomas in patients without stigmata of neurofibromatosis. Lectin binding patterns of Schwann cells and perineurial cells in neurofibroma were almost similar to those in normal peripheral nerves with an exception of faint stain of Schwann cells with HPA after neuraminidase pretreatment. This result suggests differences in extent of differentiation between schwannoma cells and neoplastic Schwann cells in neurofibroma. Specific PNA binding to perineurial cells in neurofibroma indicates the significance of this lectin as a marker of these cells.