Cutaneous microcystic/reticular schwannoma: a poorly recognized entity

Novel NONO::TFE3 fusion and ALK co-expression identified in a subset of cutaneous microcystic/reticular schwannoma

Microcystic/reticular schwannoma (MRS) is a benign variant of schwannoma with a predilection for the gastrointestinal tract and skin. To date, genetic characterization of this tumor is limited. Prompted by the identification of TFE3::NONO fusion and ALK overexpression in an index case of MRS, a cohort of tumors was collected from institutional and consultation archives of two institutions. Next-generation sequencing (NGS), TFE3 fluorescence in situ hybridization (FISH), and TFE3 and ALK immunohistochemistry were performed, while clinicopathologic variables were documented. Eighteen MRS cases were identified (35 to 85 years) arising in the skin (n=8), gastrointestinal tract (n=5), adrenal gland (n=3), abdominal wall (n=1), and unknown site (n=1). Tumors showed a circumscribed to multinodular to plexiform low-power architecture with variable amounts of microcystic/reticular and solid schwannian components. Mitotic figures were scarce (0-1/10 HPFs), and atypia was absent. S100 protein and/or SOX10 immunoreactivity was noted in the microcystic/reticular and schwannian areas of all cases. NGS performed on two cutaneous tumors yielded NONO exon 12 fusion with TFE3 exon 4, and these lesions also showed HMB45 and ALK expression. Two additional cases showed ALK expression (1 weak), while a third was positive for TFE3, but these cases failed to show ALK or TFE3 rearrangement by FISH/NGS. There were no morphologic variables that correlated with the presence of NONO::TFE3. We identified a subset of microcystic/reticular schwannomas with NONO::TFE3 fusions and ALK co-expression, adding to the cohort of mesenchymal neoplasms that show ALK overexpression without rearrangement of the ALK gene.

Microsecretory Adenocarcinoma of the Ear Canal: Novel Cutaneous Analog of a Salivary Gland Neoplasm

ABSTRACT

Microsecretory adenocarcinoma (MSA) of the salivary gland is a new entity recently added to the World Health Organization Classification of Head and Neck Tumors. This tumor is characterized by a recurrent MEF2C-SS18 translocation. We present a nodular tumor confined to the dermis of the ear canal of a 44-year-old patient, which demonstrated classic histopathologic features and molecular alteration of MSA. Specifically, the tumor was composed of numerous tubules and microcysts filled with abundant basophilic mucinous secretion and associated with a fibromyxoid stroma. The tumor cells were diffusely positive for CK7 and SOX10 and variably positive for S100 and p63. Breakapart fluorescence in situ hybridization for SS18 confirmed rearrangement of this gene. Together, these findings support a primary cutaneous MSA, presumably arising from ceruminous glands of the ear canal. Based on current knowledge of its salivary gland counterpart, cutaneous MSA is expected to be locally invasive but unlikely to recur or metastasize on complete excision.

A microcystic/reticular schwannoma in an unusual site: description of a retroperitoneal location and review of the literature

Microcystic/reticular (MRV) schwannoma has been described since 2008, but remains a rarely encountered entity. MRV has a predilection for visceral locations and has variable histologic appareances. Given its rarity and anatomic variability, this entity could raise differential diagnostic issues with other tumours and malignancies.

We describe the case of a 69-year-old male followed at IRCCS Ospedale Policlinico San Martino of Genoa for his previous history of non-Hodgkin lymphoma. A para-aortic mass was discovered during follow-up, which -due to its stability, also after chemotherapy- had been hypothesized to be a non-lymphomatous lesion; given the dimensions and the site, the mass was removed. Histological evaluation showed a nodule limited by a slight fibrous capsule and characterized by a proliferation of medium-sized fusiform cells, with elongated nuclei and scarce eosinophilic cytoplasm. Given the lack of malignant signs and the strong expression of protein S-100, a diagnosis of mesenchymal neoplasia with expression of neural markers compatible with reticular schwannoma was made. The neoplasm has not recurred since its removal.

The case we present is, at our best knowledge, the first described in the retroperitoneum, a site where the exclusion of other mesenchymal malignancies is mandatory. The rarity and variability of presentations could create problems of differential diagnosis both with mucinous-producing carcinomas or with other soft tissue tumours, with myxoid or reticular structure. The description of this case could help raise information on this rare neoplasm and help distinguish it from other malignancies, especially in unusual sites.

Case of Symptomatic Dermal Neurofibroma With Microcystic Features

ABSTRACT

A neurofibroma is a benign neural tumor arising within a peripheral nerve sheath composed of Schwann cells, fibroblasts, and immune cells involved in the nerve. Microcystic elements have been rarely described in these tumors. Neurofibromas are classically described as unencapsulated tumors of interspersed spindle cells and mast cells in a hypocellular, myxoid stroma. These tumors are most commonly dermal and seen in almost all patients with neurofibromatosis type 1; however, they may also occur sporadically, as seen in our case here. We report a 23-year-old patient with no significant medical history who presented with a dome-shaped papule on her cheek. This slow-growing mass had been present for multiple years and was soft, inflamed, and painful. Shave biopsy was collected and sent for evaluation. The shave biopsy diagnosed a benign neural tumor with features of a rare microcystic neurofibroma. This unencapsulated tumor consisted of microcystic spaces lined by oval-shaped to spindle-shaped cells in a matrix of myxoid to collagenous-like areas. Scattered lymphocytes and mast cells were noted, with few true vessels enclosing red blood cells. The stromal cells and cells lining the microcystic spaces stained S100 and SOX-10 positive. These cells had limited CD34 staining; however, most microcystic spaces were negative. Only the few true vessels stained CD31 positive. It is important to distinguish the prominent microcystic features in neurofibromas versus schwannomas by the lack of encapsulation or Antoni A features with Verocay bodies, which are typical of the latter. Further differentiating neurofibromas versus malignant peripheral nerve sheath tumors is required, where the latter should exhibit much greater nuclear atypic, higher cellularity, necrosis, hemorrhage, and increased mitotic activity. Excision of this benign microcystic neurofibroma was not deemed necessary because of lack of clinical concern and recurrent lesions.

What's new in nerve sheath tumors

Peripheral nerve sheath tumors are commonly encountered and frequently pose challenges to the pathologist and the clinician. This review discusses the wide range of entities with an emphasis on new discoveries in the past decade. Clinical, histologic, immunohistochemical, and pathogenetic findings are discussed with an emphasis on clinical implications and differential diagnosis.

Intraparenchymal schwannoma with calcification of the temporal lobe: Case report and literature review

RATIONALE

Intracranial schwannomas most frequently arise from the trigeminal nerve and the vestibular nerve. Schwannomas within the cerebral parenchyma are exceedingly rare. Additionally, calcification is an uncommon histopathological and radiological characteristic in schwannomas.

PATIENT CONCERNS

A 46-year-old man presented to us with sudden onset epileptic seizure and a 3-month history of intermittent headache. After admission, the physical and neurological examinations were all normal. Brain CT revealed an irregular, well-defined, hyperdense mass in the right temporal lobe. MRI showed a solid mass appearing iso- to hypointensity on T1-weighted imaging and heterogeneous intensity on T2-weighted imaging in the right temporal lobe; after Gd-DTPA administration, the lesion showed heterogeneous enhancement.

DIAGNOSIS

Histopathological examination revealed hyperchromatic nuclei and loose intercellular matrix with calcification. Immunohistochemical analysis demonstrated that the tumor was strongly positive for S100 protein but negative for GFAP and CK, which was consistent with a schwannoma.

INTERVENTIONS AND OUTCOMES

A surgical resection via the right temporal approach was performed. Intraoperatively, we noticed that the tumor was grayish yellow, capsuled, and located entirely within the temporal parenchyma. A gross total resection was achieved. The postoperative course was uneventful, and there was no epileptic seizure.

LESSONS

Intraparenchymal schwannoma with calcification is an uncommon histopathological and radiological characteristic in schwannomas. Intraparenchymal schwannoma with calcification is extremely rare. The early identification and appropriate surgical treatment should be highlighted.

Lumbar intraspinal microcystic/reticular schwannoma: Case report and literature review

RATIONALE

Microcystic/reticular schwannoma (MRS) is a rare histological variant of schwannoma which was initially described in 2008 with a predilection for the visceral organs. This distinct tumor had been reported to mainly affect gastrointestinal tract, subcutaneous and soft tissue, various glands and head and neck region. However, MRS involving spine is extremely rare.

PATIENT CONCERNS

The authors report the first case of MRS occurring in the lumbar (L) spinal canal of a 40-year-old male who presented with continuous pain and numbness in both feet for 2.5 years. Physical examination revealed weakness of lower extremities and hyperalgesia of both feet.

DIAGNOSES AND INTERVENTIONS

The findings of pre-operative investigation were suspicious for either a schwannoma or a spinal meningioma. Accordingly, total laminectomy, complete tumor resection, instrumentation and spinal fusion were performed. Post-operative histopathologic examination revealed a well-encapsulated neoplasm with reticular and microcystic growth pattern. Antoni A and Antoni B regions, Verocay bodies and hyalinized blood vessels were observed. And cytologic atypia, necrosis or mitosis was absent. Immunohistochemically, the tumor cells showed strong and diffuse positivity for S-100 as well as SOX 10. Therefore, a histopathological diagnosis of MRS was finally made.

OUTCOMES

The patient remains well with no evidence of recurrence at a 22-month follow-up.

LESSONS

This is the first case of MRS which is located in the L spinal canal. Awareness of this distinctive entity is helpful in preventing diagnostic pitfalls and making correct treatment strategies.

Microcystic/Reticular Schwannoma of the Frontal Lobe: An Unusual Occurrence

Schwannoma is a benign peripheral nerve sheath tumor that typically involves cranial nerves of the head and neck region. Intraparenchymal occurrence of this tumor is uncommon. Even rarer in this site is the microcystic/reticular pattern of schwannoma. This histologic variant, first described in 2008, has a predilection for visceral organs. Herein, we report the first case of microcystic/reticular schwannoma of the frontal lobe.

Morphological spectrum of peripheral nerve sheath tumors: An insight into World Health Organization 2013 classification

Introduction:

Peripheral nerve sheath tumors (PNSTs) are neuroectodermal in origin. Now these tumors are classified under World Health Organization (WHO) classification of tumors of soft tissue and bone 2013.

Objective:

To study the morphological spectrum of PNST and to study the secondary degenerative changes associated with it.

Materials and Methods:

This study was conducted from January 2010 to June 2015. The gross details of tumor and patient's demographic profiles were reviewed. The hematoxylin and eosin stained slides were reassessed and the lesions were categorized and classified as per the WHO 2013 classification. The tumors were also assessed for secondary degenerative changes.

Results:

Our study comprised 143 cases of PNST. Age of the patients ranged from 5 to 75 years. 21–30 years is the most common age of occurrence with head and neck being the most common site. The PNSTs observed in the present study were neurofibroma (NF) (61.5%), schwannoma (36%), malignant PNST (2%), and granular cell tumor (0.5%). Nearly 10% of NF fulfilled the criteria for neurofibromatosis 1 (NF1). Rare tumors such as plexiform schwannoma and granular cell tumor were also observed. Malignant tumors were larger in dimension than benign. Myxoid, cystic, and hyaline changes were commonly associated with benign tumors while necrosis, hemorrhage, and mitotic activity were seen with malignant tumors.

Conclusion:

This series highlights the pathological variants of PNST along with their morphological changes and NF1 association. It is essential to be familiar with all these variants of PNST for accurate diagnosis as they have varied biological behavior.