BackgroundSchwannomas of the colon and rectum are rare among gastrointestinal schwannomas. They are usually discovered incidentally as a submucosal mass on routine colonoscopy and diagnosed on pathologic examination of the operative specimen. Little information exists on the diagnosis and management of this rare entity.The aim of this study is to report a case of cecal schwannoma and the results of a systematic review of colorectal schwannoma in the literature.Main bodyPubMed, Scopus, and Cochrane database searches were performed for case reports and case series of colonic and rectal schwannoma.Ninety-five patients with colonic or rectal schwannoma from 70 articles were included. Median age was 61.5 years (59% female). Presentation was asymptomatic (28%), rectorrhagia (23.2%), or abdominal pain (15.8%). Schwannoma occurred in the left and sigmoid colon in 36.8%, in the cecum and right colon in 30.5%, and in the rectum in 21.1%. Median tumor size was 3 cm and 56.2% of patients who underwent preoperative colonoscopy had a typical smooth submucosal mass. At pathology, 97.9, 13.7, and 5.3% of schwannomas stained positive for S100, vimentin, and GFAP, respectively. The median mitotic index was 1/50.ConclusionsColorectal schwannoma is a very rare subtype of gastrointestinal schwannoma which occurs in the elderly, almost equally in men and women. Schwannoma should be included in the differential diagnosis of a submucosal lesion along with gastrointestinal stromal tumor, neuro-endocrine tumors, and leiomyoma-leiomyosarcoma. Definitive diagnosis is based on immunohistochemistry of the operative specimen. Rarely malignant, surgery is the mainstay of treatment.
Melanocytic matricoma is a rare benign pilar tumor characterized by matrical differentiation and interspersed dendritic melanocytes. It may show cellular atypia and brisk mitotic activity. Histological characterization of some lesions may be difficult. In addition, because the reported cases are few and have limited follow-up, there is insufficient experience to define outcome-based criteria for malignancy. Some cases of melanocytic matricoma with more prominent atypia have been reported as malignant, but their clinical behavior is uncertain. We present a melanocytic matricoma with interspersed benign dendritic melanocytes, but moderate basaloid atypia, focally brisk mitotic activity, and atypical mitoses. Despite the apparently good delimitation of this tumor, higher magnification revealed a slightly irregular border. However, overt malignant features such as necrosis, frank asymmetry, deep infiltration, and ulceration were not present. This tumor showed a complex aberrant genomic profile with multiple whole chromosomes or chromosomal arms, losses, and duplications. The tumor mutational burden was high. A loss-of-function alteration in CDKN2A and a loss-of-function mutation in TP53 were also present. This unexpected molecular profile contrasts with the relatively bland histology of the tumor and is in line with the difficulties in microscopic differential diagnosis between melanocytic matricoma and an indolent malignant pilomatrical tumor. We suggest that molecular studies and longer follow-up periods may help to further understand and more precisely categorize borderline pilomatrical tumors with melanocytic hyperplasia.
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