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Sclerosing rhabdomyosarcoma (RMS) is a rare subtype of RMS with unique prominent stromal hyalinization and a pseudovascular architecture. It overlaps morphologically with spindle cell RMS and poses both diagnostic and therapeutic challenges because of its rarity and aggressive clinical course. In this article, we report a case of sclerosing RMS arising from a prior craniotomy site, which demonstrated both sclerosing and spindle cell components. A literature review of RMS with sclerosing morphology identified 122 cases. Our review documents the following: sclerosing RMS occurs in both childhood and adult populations, has a predilection for the head and neck areas, and has a worse prognosis in adults. Sclerosing RMS harbors a high frequency of MYOD1 mutations, conferring a poor clinical outcome. Sclerosing RMS and spindle RMS likely represent a morphologic spectrum of one entity.

PEComas are mesenchymal neoplasms composed of perivascular epithelioid cells (PEC) and include a spectrum of tumors. PEComas and malignant melanoma share common morphological, immunohistochemical, and ultrastructural features, such as epithelioid cell morphology and melanocytic immunophenotype. Melanocytic markers commonly expressed in PEC tumors include HMB-45, Melan-A/MART-1, tyrosinase, microphthalmia transcription factor (MITF), and occasionally, S100. Given this morphological and immunophenotypical overlap, the differential diagnosis between a PEComa and malignant melanoma can represent a challenge. Additional diagnostic difficulty is the differentiation of melanoma and PEComa from clear cell sarcoma that is indistinguishable from melanoma based on the immunohistochemical profile. Recent studies have shown that MUM-1, a known lymphocyte marker shows positive immunostaining in nevi and melanomas, its expression in PEComas and clear cell sarcoma, however, has not been previously addressed. In this study, the authors analyzed MUM-1 expression using immunohistochemistry in PEComas (n = 8), the PEComa family members, angiomyolipomas (n = 13), and clear cell sarcomas (n = 11) and compared the staining pattern with malignant melanomas (n = 25), both primary (n = 14) and metastatic (n = 11). It was found that 92.3% of primary melanomas and 81.3% of metastatic melanomas were MUM-1 positive. In contrast, MUM-1 was only weakly positive in only 25% of PEComas and negative in all angiomyolipomas. MUM-1 expression was noted in 72.7% of clear cell sarcomas. The study demonstrated differential MUM-1 expression between PEComas and other true melanocytic tumors and suggested that the addition of MUM-1 to the usual panel of melanocyte markers could be a helpful adjunctive study to aid in the differential diagnosis between these entities.

The DNA-binding factor TFE3 is closely related to microphthalmia-associated transcription factor (MiTF) and is over-expressed in alveolar soft part sarcoma (ASPS) and select renal cell carcinomas. Reports of TFE3 expression in PEComa prompted investigation into TFE3 expression among other members of the putative MiTF group of neoplasms. The authors examined cases of PEComa (n = 6), conventional angiomyolipoma (AML; n = 22), metastatic melanoma (n = 16), and clear cell sarcoma (CCS; n = 9) for TFE3 expression. Nuclear immunostaining was observed in 74% (39/53) of cases, as follows: 5/6 PEComas, 18/22 AMLs, 10/16 metastatic melanomas, and 6/9 CCSs. However, with the exception of PEComas, compared with ASPS controls, TFE3 staining was significantly less intense in the tumors examined. These results illustrate that TFE3 immunoreactivity is detectable in other members of the MiTF family of neoplasms. For this reason, such neoplasms warrant consideration in the differential diagnosis with nuclear TFE3 immunoreactivity, particularly when staining is focal and less intense.

Hibernomas are rare, benign tumors that contain neoplastic cells that are histologically similar to those of brown adipose tissue. The most common sites of these tumors have been the back and thighs; head and neck involvement has been rare. We describe the case of a 54-year-old woman who presented with a 1-year history of a large, asymptomatic, lateral neck mass. Based on imaging findings and fine-needle aspiration cytology, a hibernoma was suspected, although a liposarcoma could not be ruled out prior to surgery. The mass was completely resected. On postoperative analysis, the tumor was grossly and microscopically consistent with a cervical hibernoma. Although hibernomas are rare, they are important entities and should be considered in the differential diagnosis of a soft-tissue mass of the head or neck.

A dermoid cyst is an ectodermally differentiated form of teratoma. Its occurrence in the parotid gland is very rare. Such a presentation must be properly evaluated in order to rule out malignancy. We describe the diagnostic evaluation and surgical management of a parotid dermoid cyst in an 18-year-old man. We also review the embryologic pathogenesis of the tumor and the usefulness of the physical examination, preoperative fine-needle aspiration cytology, magnetic resonance imaging, and computed tomography in evaluating the extent of the tumor, its histologic features, and its cystic characteristics. Finally, we discuss the role of surgical management in terms of preserving facial nerve integrity and preventing recurrence.

We describe a case of a venous hemangioma that arose in the optic nerve sheath of the orbital apex in a 28-year-old man who presented with progressive vision loss. To the best of our knowledge, this is the first reported case of a venous hemangioma occurring at this location. A definitive diagnosis and partial excision was achieved via an endoscopic transsphenoethmoid approach with interactive, computer-assisted, frameless stereotactic surgical navigation. The intervention resulted in minimal morbidity, demonstrating yet again that this surgical approach is a safe and effective way to treat lesions of the orbital apex.