Perianal basal cell carcinoma is a very rare tumor accounting for only 0.2% of the anorectal tumors. It must be distinguished from basaloid carcinoma of the anus, which resembles it histologically but shows a much more aggressive behavior, metastasizes early, and often proves fatal, thus requiring different therapy. Differential diagnosis of both entities by light microscopy may be difficult. Five cases of perianal basal cell carcinoma and five cases of basaloid carcinoma were studied by means of immunohistochemistry and flow cytometry. Some immunohistochemical markers, such as epithelial membrane antigen, carcinoembrionic antigen, and keratins, as well as the lectin Ulex europaeus agglutinin I stained basaloid carcinoma and were negative for basal cell carcinoma. In contrast, the monoclonal antibody Ber-EP4 seems to be a good marker for perianal basal cell carcinoma and useful in differentiating it from basaloid carcinoma of the anus. Basaloid carcinomas are associated with a significantly higher S-phase fraction than are perianal basal cell carcinomas (p < 0.01).

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The hibernoma is an uncommon, benign soft tissue tumor arising from vestigial remnants of so-called brown fat. It most commonly occurs in the interscapular regions, but there are also a number of cases originating in sites normally devoid of brown fat. Most of these tumors are subcutaneous; nevertheless, deep-seated hibernomas have been reported in intrathoracic sites. A hibernoma in the head and neck region is very rare, and few cases in this location have been reported. [1][2][3][4] We report a case of hibernoma in the submandibular space with immunohistochemical and ultrastructural study. Case ReportA 55-year-old male was admitted with a six-month history of a slow-growing, painless mass in the submandibular area. There was no significant past medical or surgical history and a thorough examination of the head and neck revealed no other abnormalities. All laboratory studies were normal. With the clinical diagnosis of primitive submandibular gland tumor, the patient was scheduled for surgery. The surgical specimen consisted of a yellow-brown, well demarcated and encapsulated tumor measuring 3.5 x 2.5 cm, joined to the submandibular gland (Figure 1). Microscopically, the neoplasm displayed a distinct lobular pattern and four types of cells could be recognized: most cells contained numerous small round lipid vacuoles that did not indent the regular and spherical nucleus (cells with moruloid or mulberry appearance). The second type of cells were larger and showed an eccentrically displaced nucleus, indistinguishable from a normal mature fat cell (Figure 2). The third type of cells contained lipid vacuoles which indented the central nucleus, then became indistinguishable from a multivacuolated lipoblast ( Figure 3A), and the fourth type consisted of isolated polygonal cells with eosinophilic granular cytoplasm and small, regular spherical nucleus ( Figure 3B). Mitoses and pleomorphism were absent. A rich vascular network was found. The histological features were considered to be those of a hibernoma. Ultrastructurally, the cells were polygonal with multiple well-defined droplets of lipid of variable size and large round to oval mitochondria which occupied much of the cytoplasm remaining between the fat droplets ( Figure 4A). These mitochondria were tightly packed, with highly organized and parallel straight transverse cristae ( Figure 4B). The mitochondrial matrix was of medium to high density and showed large and abundant dense granules. The endoplasmic reticulum was very scarce and the Golgi apparatus inconspicuous. The nuclei were round and contained uniformly distributed chromatin condensed under nuclear membrane. In some cells, multiple intracytoplasmic lipid droplets caused scalloping of the centrally situated nucleus. Hibernoma cells were surrounded by a well-defined basal lamina. Immunohistochemically, tumor cells showed diffuse vimentin reactivity. Staining for S-100 protein was focally positive. Hibernoma cells did not react with antibodies directed against cytokeratin, CD68, epithelial membrane antigen (...