Mucosal Schwann cell “hamartoma”: clinicopathologic study of 26 neural colorectal polyps distinct from neurofibromas and mucosal neuromas. Am J Surg Pathol. 2009;33:781-787. [PMID: 19065103 DOI: 10.1097/pas.0b013e31818dd6ca]

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

The frequency and morphological spectrum of gastrointestinal peripheral nerve sheath tumors (PNSTs) from consecutive case material has not been studied in the c-KIT era. We reviewed all mesenchymal gastrointestinal (GI) lesions at our departments according to current diagnostic criteria. PNSTs formed the third commonest group of mesenchymal GI tumors with a lower frequency (< or =5%) compared to gastrointestinal stromal tumors (GISTs; approximately 50%) and smooth muscle neoplasms ( approximately 30%). Granular cell tumors (GCTs; n = 31) and schwannomas (n = 22) were the most common types of PNSTs encountered. Rare tumors included neurofibromatosis 1 (NF1)-associated PNSTs (n = 5) and gastric perineurioma (n = 1). Thirteen schwannomas (including also some recent cases) were initially diagnosed as GIST, leiomyoma, or neurofibroma. Unusual histological variants included sigmoid GCT with prominent lipomatous component (n = 1), reticular-microcystic schwannoma of small (n = 1) and large (n = 1) bowel, NF1-associated gastric schwannoma (the first case to date), and psammomatous melanotic colonic schwannoma unrelated to Carney complex (n = 1). PNSTs coexisted with GIST in four patients (three had definite NF1). In conclusion, PNSTs of the GI tract are rare uniformly benign neoplasms that may show schwannian, perineurial, fibroblastic, or mixed differentiation. Most of them (92%) occurred sporadically unassociated with NF1 or NF2. Gastrointestinal PNSTs are still underrecognized by general pathologists. Awareness of their diverse morphology will help to avoid confusing them with smooth muscle neoplasms and GIST that they may closely mimic.

Palisaded encapsulated ("solitary circumscribed") neuroma of the oral cavity: a review of 55 cases

We describe the clinicopathologic characteristics of 55 oral palisaded encapsulated (solitary circumscribed) neuromas (PEN/SCN). Fifty-five cases of PEN/SCN in 54 patients were reviewed. Lesions were categorized according to their histologic pattern, partial or complete encapsulation, presence of Verocay bodies and presence of a parent peripheral nerve. In 13 selected cases immunohistochemical evaluation for neuronal markers (S-100, GFAP, NFP, EMA) was performed. When immunoreaction with EMA was weak, claudin-1 and glut-1 stains were utilized. Thirty-eight patients were men and 16 were women. Mean patient age was 48 years (SD: +/-14). The vast majority involved the masticatory (palate and gingiva) mucosa (76.4%) followed by the labial mucosa, the tongue and buccal mucosa. Recurrence was recorded in only one case. Histologically, 34 lesions had a lobular pattern, 10 were plexiform, 7 fungating and 4 multilobular. Stroma was limited, but focal myxoid changes were seen at the periphery of the lobules. Only one predominantly myxoid lesion was encountered. The number of intralesional axons varied, but the ratio of Schwann cells to axons was generally less than 1:2. Most lesions (89%) were only partially surrounded by perineurium. Tumor cells were S-100 positive and GFAP negative. The parent nerve was identified in 50% of the cases. Overlying epithelium was generally atrophic. Peritumoral connective tissue was generally unremarkable, but chronic inflammation was present in five cases. PEN/SCN is a relatively common peripheral nerve sheath tumor. Generally, its diagnosis is simple. GFAP may be of help to distinguish PEN/SCN from other peripheral nerve sheath tumors (schwannoma, neurofibroma, traumatic neuroma) in cases where histomorphologic features may be confusing. Finally, pathologists should be aware of the occurrence of plexiform and multilobular PEN/SCN variants, to avoid misinterpretation as plexiform neurofibroma or schwannoma.

Early Colonic Perineurioma: A Report of 11 Cases

Colonic perineurioma has been depicted as characterized by a mucosal proliferation of monomorphic spindle perineurial cells leading to an evident separation, distortion, and entrapment of colonic crypts. The authors, however, believe that a sizable subset of the cases differ in that they display only a limited perineurial proliferation leading to only mild crypt separation without crypt entrapment. This morphological variant (early perineurioma) has not yet been documented. The authors herein present the clinicopathological and immunohistochemical features of 11 cases. Polyp size ranged from 2 to 4 mm, and 8 (73%) were located in the sigmoid. Histologically, they revealed small, frequently noncontiguous nests or bundles of uniform round to oval cells, causing slight separation of parallel or mildly distorted crypts, which displayed a serrated/hyperplastic architecture in 8 (73%) cases. Immunostaining for perineurial markers showed strong expression for claudin-1, GLUT-1, and collagen type IV and weak reactivity for epithelial membrane antigen. In conclusion, early perineurioma is a morphological variant of colonic perineurioma in which the perineurial proliferation is limited and consequently more difficult to recognize. Using perineurial markers is helpful in reaching an accurate diagnosis.

Mucosal Schwann cell “Hamartoma”: A new entity?

Schwannoma is a well-described, benign nerve sheath tumor of the soft tissue, but is rare in the gastrointestinal tract. Gastrointestinal schwannomas are often incidentally discovered as small polypoid intraluminal lesions. In this report, we describe the clinicopathologic and immunohistochemical features of a distinctive neural mucosal polyp composed of a diffuse cellular proliferation of uniform bland spindled cells in the lamina propria that entraps the colonic crypts. Immunohistochemical analysis revealed strong and diffuse positivity for the S-100 protein. To avoid confusion of these solitary colorectal polyps containing pure spindled Schwann cell proliferation in the lamina propria with neural lesions that have significant association with inherited syndromes, it is better to use the designation “mucosal Schwann hamartoma”.