Microcystic/Reticular Schwannoma: A Distinct Variant With Predilection for Visceral Locations

Abstract

Schwannomas are benign, generally nonrecurring tumors most frequently arising in the subcutaneous tissue of adults with no sex predilection. Herein we report 10 cases of a distinctive morphologic variant of schwannoma with predominantly microcystic-reticular morphology and characterize the clinicopathologic spectrum. The age at presentation ranged from 11 to 93 years (median age 63 y). The tumor size ranged from 0.4 to 23 cm (median size 4.3 cm). Five tumors arose in the gastrointestinal tract, most often in the submucosa. Two cases arose in subcutaneous tissue and 1 case each in the upper respiratory tract, the adrenal gland, and deep soft tissue. None of the patients had features of neurofibromatosis type 1 or type 2 (NF1, NF2). Histologically 8 tumors were circumscribed but unencapsulated and 2 cases located in the subcutaneous fat were circumscribed and encapsulated. At visceral locations, focally pushing margins and microscopic foci of infiltration into surrounding parenchyma were seen. All cases showed a striking microcystic and reticular lesional growth pattern with anastomosing and intersecting strands of spindle cells with eosinophilic cytoplasm distributed around islands of myxoid or collagenous/hyalinized stroma. The nuclei were round, oval, and tapered and showed inconspicuous nucleoli. Three cases had smaller areas resembling conventional schwannoma. Mitotic activity did not exceed more than 3 mitoses/50 high-power fields (HPF) (median 1/30 HPF). Pleomorphism and necrosis were absent. All tumors showed strong nuclear and cytoplasmic positivity for S-100 and variably strong glial fibrillary acidic protein staining. A surrounding tumor capsule was highlighted with epithelial membrane antigen in 2 out of 10 cases. Smooth muscle actin, Desmin, Pan-CK, AE/AE3, Cam5.2, and p-63 were negative in all cases evaluated. Neurofilament protein highlighted axons in one out of 7 cases investigated. CD117 showed weak focal positivity in 1 out of 4 cases. Follow-up data were available in 7 cases (median duration 15 mo). None has recurred to date. Microcystic schwannoma represents a distinctive morphologic variant of schwannoma with predilection for visceral locations. Recognition of this distinct entity is essential to avoid confusion with malignant tumors, especially in the gastrointestinal and upper respiratory tracts.

Peripheral nerve sheath tumors of the gastrointestinal tract: a multicenter study of 58 patients including NF1-associated gastric schwannoma and unusual morphologic variants

“…Reticular-microcystic schwannoma is a recently defined rare variant with a predilection for visceral sites [27]. Including our two cases, a total of eight cases of this rare variant were reported in the GI tract; three from the large bowel, three from the small bowel, and two from the stomach [27,28].…”

“…Including our two cases, a total of eight cases of this rare variant were reported in the GI tract; three from the large bowel, three from the small bowel, and two from the stomach [27,28]. The striking predilection of this variant for the intestine contrasts with its rarity in the stomach where most GI schwannomas occur.…”

Microcystic/Reticular Schwannoma of the Proximal Sigmoid Colon: Case Report With Review of Literature

“…Subsequently to that series, 7 more cases [3][4][5][6] of this variant involving the luminal gastrointestinal tract have been described. Adding to these recent publications, we report another example of this rare variant that was initially identified in our department well before publication of the 2008 series 2 and describe for the first time to our knowledge ultrastructure findings and significant differential diagnostic considerations.…”

“…Scattered inflammatory cells were present, whereas nodular aggregates of lymphocytes were rare. 2,6 In their group of 10 cases, 5 cases were located in the gastrointestinal tract. Of these, 4 cases were located in the submucosa and were circumscribed but unencapsulated.…”

Solitary Fibrous Tumor of the Adrenal Gland with Unusual Immunophenotype: A Potential Diagnostic Problem and a Brief Review of Endocrine Organ Solitary Fibrous Tumor

“…Apart from solitary fibrous tumors, other spindle cell neoplasms that have been reported in the adrenal gland include perineurioma [20], schwannoma [21,22], smooth muscle neoplasm such as leiomyoma [23], and pleomorphic leiomyosarcoma [24] as well as primary sarcomatoid adrenocortical carcinoma [25]. Although S-100 positivity has been described in solitary fibrous tumor Fig.…”