Primary cutaneous perivascular epithelioid cell tumor (PEComa): Five new cases and review of the literature.

PEComas represent a family of uncommon mesenchymal tumors composed of "perivascular epithelioid cells" with a distinct immunophenotype that typically shows both myogenic and melanocytic differentiation. The PEComa family includes angiomyolipoma (AML), clear cell "sugar" tumor of the lung and extra pulmonary sites, lymphangioleiomyomatosis and clear cell myomelanocytic tumor of the falciform ligament/ligamentum teres. Very rarely, PEComas may arise in the skin. Primary cutaneous PEComas typically display a dermal proliferation of epithelioid cells with pale, clear, or granular pink cytoplasm arranged in nests and trabecula with an intervening arborizing network of delicate capillaries. Primary cutaneous PEComas have a lower frequency of myogenic marker expression than their deep soft tissue and visceral counterparts. They also often express strong diffuse CD10, leading to potential confusion with metastatic renal cell carcinoma. Most cases behave indolently. We report 5 additional cases of this rare entity. All showed classic histologic features and expression of either HMB-45 and/or Melan-A/MART-1. Four cases were tested for myogenic markers (2 were positive & 2 were negative). Three cases were tested for CD10 (all 3 were positive). All of our cases with clinical follow-up behaved indolently. Table 1 provides a summary of findings for all 5 cases in our series.

Magnetic resonance imaging of rectal cancer: staging and restaging evaluation.

Magnetic resonance imaging is used to non-invasively stage and restage rectal adenocarcinomas. Accurate staging is important as the depth of tumor extension and the presence or absence of lymph node metastases determines if an individual will undergo preoperative neoadjuvant chemoradiation. Accurate description of tumor location is important for presurgical planning. The relationship of the tumor to the anal sphincter in addition to the depth of local invasion determines the surgical approach used for resection. High-resolution T2-weighted imaging is the primary sequence used for initial staging. The addition of diffusion-weighted imaging improves accuracy in the assessment of treatment response on restaging scans. Approximately 10%-30% of individuals will experience a complete pathologic response following chemoradiation with no residual viable tumor found in the resected specimen at histopathologic assessment. In some centers, individuals with no residual tumor visible on restaging MR who are thought to be at high operative risk are monitored with serial imaging and a "watch and wait" approach in lieu of resection. Normal rectal anatomy, MR technique utilized for staging and restaging scans, and TMN staging are reviewed. An overview of surgical techniques used for resection including newer, minimally invasive endoluminal techniques is included.