Epithelial sheath neuroma: a new entity

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.

Unraveling the Mysteries of Perineural Invasion in Benign and Malignant Conditions

Perineural invasion (PNI) is defined as the dissemination of neoplastic cells within the perineural space. PNI can be a strong indicator of malignancy and is linked to poor prognosis and adverse outcomes in various malignant neoplasms; nevertheless, it can also be seen in benign pathologic conditions. In this review article, we discuss various signaling pathways and neurotrophic factors implicated in the development and progression of PNI. We also describe the methodology, benefits, and limitations of different in vitro, ex vivo, and in vivo models of PNI. The spectrum of presentation for PNI can range from diffuse spread within large nerves ("named" nerves) all the way through localized spread into unnamed microscopic nerves. Therefore, the clinical significance of PNI is related to its extent rather than its mere presence or absence. In this article, we discuss the guidelines for the identification and quantification of PNI in different malignant neoplasms based on the College of American Pathologists (CAP) and World Health Organization (WHO) recommendations. We also describe benign pathologic conditions and neoplasms demonstrating PNI and potential mimics of PNI. Finally, we explore avenues for the future development of targeted therapy options via modulation of signaling pathways involved in PNI.

Reparative Perineural Hyperplasia in the Gastric Wall: A Histologic Mimic of Perineural Invasion

Reparative perineural hyperplasia is an incidental and probably underreported reactive histologic finding thus far only reported in the setting of healing wounds or adjacent to a dermatofibroma in cutaneous specimens. It is characterized by a focal concentric proliferation of cytologically bland spindled perineurial cells and is hence considered a benign histologic mimic of neoplastic perineural invasion. Thus, it may present a diagnostic pitfall and we therefore consider it as a valuable entity to be aware of. To the best of our knowledge, this brief case report is the first to convey that reparative perineural hyperplasia may also occur in the gastrointestinal tract. It may therefore be a ubiquitous reactive histological phenomenon relating to previous surgical or traumatic wounds in various sites, that is, outside the thus far established setting of skin reexcision specimens.

Dermal hyperneury

Dermal hyperneury (DN) is a rarely reported form of small nerve hypertrophy characterized by an exaggerated size and prominence of dermal nerve fibers. Clinically, it can present with or without visible lesions, within a syndrome or sporadically, and in solitary or multiple fashion. The syndromes most commonly associated with DN include multiple endocrine neoplasia 2B and 2A, neurofibromatosis type II, and Cowden syndrome. Patients with syndrome-associated DN have an increased risk for various malignancies. Sporadic DN has been reported either in association with cutaneous tumors/reactive lesions, such as nodular prurigo, or in idiopathic form, where it can present with multiple DN lesions. There is a morphologic overlap between mucocutaneous neuromas and DN, as the former can have the appearance of either bulkier circumscribed lesions or tortuous and hyperplastic nerves more akin to DN. Epithelial sheath neuroma also shares a similar appearance to DN, from which it can be distinguished by a squamoid-appearing and thickened perineurium.

Epithelial sheath neuroma with extension to the subcutis

Epithelial sheath neuroma (ESN) is a rare entity, histologically showing enlarged nerves in the superficial dermis surrounded by cytologically bland keratinocytes, classically presenting clinically as an erythematous papule or nodule on the back of middle-aged to elderly individuals. Clear-cut recommendations for treatment are not available, with many reports citing biopsy alone or simple excision as curative. We report a case of biopsy-proven ESN presenting as a significantly painful nodule in an elderly woman. Surgical excision was performed for symptom control and the residual ESN was found to extend deep into the subcutis.

Reexcision Perineural Invasion and Epithelial Sheath Neuroma Possibly on a Spectrum of Postinjury Reactive Hyperplasia Mediated by IL-6

Epithelial sheath neuroma is a rarely recognized but established entity in the medical literature. First described in 2000 by Requena et al, there have only been 7 published cases to date, mostly in female patients and presenting as symptomatic solitary lesions on the back without a known history of trauma. In 2006, Beer et al described and reviewed a dozen cases in which epithelial sheath neuroma-like features were seen in the advent of a surgical procedure, which was termed "re-excision perineural invasion" and attributed to possible eccrine duct implantation during surgery. Our case is a 66-year-old male patient who underwent an excision of a melanocytic neoplasm in which a reactive epithelial sheath neuroma was incidentally discovered in the excision specimen, adjacent to the biopsy site cicatrix. Histologically, there was benign cutaneous nerve hyperplasia with a proliferation of squamous epithelium in intimate apposition to the nerve bundles in the superficial dermis. We postulate that the process active in the formation of re-excision perineural invasion is the same as in epithelial sheath neuroma and that minor trauma not appreciable on histologic examination is responsible in the latter entity. We performed IL-6 staining and documented that IL-6 was upregulated at the interface of the nerve and reactive epithelium, but was absent in nerves distant from the site of surgery, suggesting that IL-6 may be essential to the lesion's development. The recognition of reactive epithelial sheath neuroma including the subcategory of re-excision perineural invasion is crucial for the dermatopathologist to prevent mislabeling this reactive entity as a perineural squamous cell carcinoma, which has clinical consequences for the patient such as wider re-excision and radiation treatment. Additionally, we have identified a potential pathophysiologic basis for this lesion.

Histopathologic pitfalls of Mohs micrographic surgery and a review of tumor histology

Mohs micrographic surgery is a specialized subset of staged surgical excisions with each subsequent stage being driven largely by the histologic findings of the previous stage. Therefore, it is imperative that histologic analysis is performed in an accurate manner. Frozen section and tissue flattening is a crucial step in Mohs surgery. Frozen sections introduce certain artifacts and these artifacts must be interpreted in the correct context. Basal and squamous cell carcinomas are the most common tumors encountered in Mohs micrographic surgery, and their histopathology is also associated with certain "pitfalls". Basal cell carcinoma should be distinguished from hair follicles, folliculocentric basaloid proliferations, poromas, nevus sebaceous, desmoplastic trichoepitheliomas, and spiradenomas, to name but a few histologic entities. Similarly, squamous cell carcinoma should be distinguished from hypertrophic actinic keratoses, pseudoepitheliomatous hyperplasia, sebaceous carcinoma, and microcystic adnexal carcinoma. In addition, there are numerous subtypes of basal cell and squamous carcinomas that the Mohs surgeon should be aware of due to differences in the biologic behavior of these tumors. This review presents a number of the common histologic pitfalls of Mohs micrographic surgery and a review of tumor histology.

Epithelial sheath neuroma: evidence supporting a hyperplastic etiology and epidermal origin

An epithelial sheath neuroma (ESN) is a rare benign process of unknown pathogenesis, which is characterized histologically by multiple enlarged peripheral nerve fibers ensheathed by mature squamous epithelium. The histologic features can elicit concern for carcinomatous perineural invasion. The process is limited to the superficial dermis and is surrounded by a loose myxoid stroma, lymphocytic infiltrate and sometimes prominent infundibular cysts. The etiology of this peculiar entity has been debated and theories include a benign neoplasm, a hamartoma or an unusual reactive hyperplasia. There are only seven prior cases reported of ESN in the literature. Our case presented here is the first report to show connection of the ESN to the overlying epidermis and reactive epidermal hyperplasia. This suggests that ESN is indeed an unusual form of benign reactive hyperplasia. In addition, the clinical setting in this case was of pruritus and scratching in a background of papular urticaria, supporting the previous notion that ESN is probably a response to an external stimulus such as rubbing.

Perineural growth of benign cutaneous sweat gland tumors: a hitherto unrecognized phenomenon unassociated with malignancy

BACKGROUND

Cutaneous intraneural reactive epithelial proliferations mimicking malignancy include epithelial sheath neuroma, re-excision perineural invasion and reactive neuroepithelial aggregates. Nevertheless, intraneural growth of benign sweat gland tumors has not been reported before.

AIMS

To report a predominantly intraneural proliferation of morphologically bland sweat gland tumors, describe their clinicopathological features and correlate them with survival.

RESULTS

We analyzed a spiradenoma and a hidradenoma with a prominent intraneural growth, occurring on the back of the 19-year-old woman and on the arm of the 53-year-old woman. Both lesions presented as a painful and slightly raised papule. After complete excision, an uneventful clinical course was observed during the follow-up period of 52 and 54 months. Pathologically, the most striking feature was an almost exclusive intraneural growth within the peripheral nerves of the deep dermis and subcutis.

CONCLUSION

We report for the first time the predominantly intraneural growth of benign sweat gland tumors. Although their histogenesis is unknown, perineural displacement due to previous surgery or trauma, as well as development from intraneural embryological epithelial remnants remains possibilities. Long-term follow-up of our patients suggests that intraneural growth of otherwise bland sweat gland tumors does not signify malignancy. Complete excision appears to be sufficient treatment procedure.

Reexcision perineural invasion: a mimic of malignancy

The presence of epithelium in the perineural space is typically associated with invasion by malignant tumors. In this report, bland-appearing epithelium was identified in the perineural space associated with a dermal reparative reaction after removal of a melanoma in 4 patients. After exclusion of possible squamous cell carcinoma and immunohistochemistry, a diagnosis of reexcision perineural invasion was made. The report illustrates the features of this uncommon and little recognized entity which has not been previously reported in the dermatology or dermatopathology literature. A lack of appreciation of the condition may lead to a misdiagnosis of malignancy, especially squamous cell carcinoma. The cases also highlight the need for good clinical correlation when examining reexcision specimens. There may be increased recognition of reexcision perineural invasion with the rise in reexcisions that are being performed, with some surgeons reexcising Spitz nevi and dysplastic nevi, for example.

Epithelial Sheath Neuroma: A Case Report and Discussion of the Literature

Here, a case of a rare epithelial sheath neuroma (ESN) is reported. A 49-year-old white female presented with a 5 mm solitary, slightly raised, erythematous, itchy papule on her right upper back. The clinical impression was consistent with an inflamed nevus. The patient had no past medical history of malignancy or a family history of neurofibromatosis. There was no prior trauma, surgical procedures, or skin disease at the site. After excision, the patient has had no recurrence at the surgery site during a 4-months follow-up period. ESN is characterized by enlarged nerve fibers ensheathed by a sometimes keratinized squamous epithelium located in the superficial dermis where large nerves are not normally found. It is believed to be a benign neoplasm and simple excision is curative. The histologic differential diagnosis of ESN is presented, and possible mechanisms of its pathogenesis are discussed. It is important for the pathologist and dermatologist to be cognizant of this lesion to prevent misdiagnosis of perineural invasion.

Peritumoral Fibrosis in Basal Cell and Squamous Cell Carcinoma Mimicking Perineural Invasion

BACKGROUND

Perineural invasion (PI) in cutaneous basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) is linked to an aggressive course. We describe a histologic mimic for PI that we termed peritumoral fibrosis (PF).

OBJECTIVE

To describe the morphologic changes associated with PF and to determine the incidence of PF and PI in Mohs frozen sections of BCC and SCC.

MATERIAL AND METHODS

All cases of BCC and SCC that were treated by Mohs micrographic surgery (MMS) at the Skin and Cancer Center, University of Florida College of Medicine, Gainesville, Florida, and the Center for Dermatology and Skin Surgery, Tampa, Florida, during the period from January 1, 2003, to August 1, 2004, were reviewed for the presence of PI and PF. The latter was defined as the presence of concentric layers of fibrous tissue that either surround and/or were surrounded by tumor formations mimicking perineural or intraneural invasion. Seven hundred six cases of BCC and 264 cases of SCC were surveyed. Eleven cases (10 BCC and 1 SCC) with equivocal areas were destained, and immunohistochemical staining with S-100 protein was performed, proving actual PI in all of these cases. Available original hematoxylin-eosin biopsy slides were correlated with the MMS frozen sections.

RESULTS

PF was noticed in 4.5% of SCCs and 5.8% of BCCs. The incidence of unequivocal PI was noted to be 2.6% in SCC and 2.1% in BCC.

CONCLUSION

We describe a specific pattern of fibrosis noted in BCC and SCC that we called PF. It shows concentric layers of fibrous tissue surrounding and/or surrounded by tumor formations and resembles carcinomatous perineural and/or intraneural invasion. Moreover, PF was found to be a sensitive marker for PI. Mohs micrographic surgeons should be aware of this phenomenon to avoid triggering unnecessary steps in managing these cases, such as irradiation.

A Case of Simultaneous Retroauricular Traumatic Neuroma and Arteriovenous Aneurysm

Traumatic neuroma is a well-defined clinicopathologic entity that is seldom associated with vascular neoformations. We describe the case of a patient with a postsurgical retroauricular neuroma that was associated with a coexisting arteriovenous aneurysm. We also performed an extensive immunohistologic characterization of the traumatic neuroma.

Reactive neuroepithelial aggregates of the skin

A peculiar, apparently reactive, microscopic structure of the skin was observed in 5 patients. It is characterized histologically by a bundle of nerve fibers partially or completely ensheathed by bland nonkeratinizing squamous epithelium. In 2 patients, the specimens were reexcision specimens, in which this structure was found amid active postbiopsy repair. In the remaining 3 patients, there was no history of previous excision or trauma at the lesional sites, and the background changes were consistent with either folliculitis or prurigo nodularis. This structure, when viewed in isolation, resembles carcinomatous perineural invasion. This structure and comparable structures observed in extracutaneous sites have often been referred to as "perineural invasion" in the literature, but the author proposes the term reactive neuroepithelial aggregate (RNEA) to denote its reactive nature.

[Squamous epithelial carcinomas of the face with neurotropic growth]

BACKGROUND AND OBJECTIVE

Invasion of squamous cell carcinoma of the head and neck into cutaneous nerves is rare and can easily be missed. Perineural outgrowth into cerebral nerves may result in severe pain or neurological disturbances. In addition, these carcinomas more often recur or metastasize and therefore are associated with a poor prognosis.

PATIENTS/METHODS

We report on two patients with squamous cell carcinoma of the dorsum of the nose and lower lip exhibiting neurotropic growth.

RESULTS

Histology showed pleomorphic keratinocytes growing deep into the subcutaneous tissue and bone, respectively. The presence of few pleomorphic keratinocytes could be only confirmed by immunohistochemistry, though indicated by a perineural lymphocytic infiltrate. In both patients, several re-excisions were necessary to achieve cure.

CONCLUSIONS

In neurotropic squamous cell carcinoma a consequent radical micrographic surgery as well as neurological and radiological investigations are mandatory. We also review the literature.