Pilonidal sinus associated with cellular blue nevus. A previously unrecognized association.J Cutan Pathol. 2007 Dec;34(12):942-5.

A neoplasm associated with a pilonidal sinus (PS) is a rare occurrence in the course of a common disease. Early detection is imperative. To our knowledge, pilonidal disease associated with a cellular blue nevus (CBN) has not been reported. There is a 10% diagnostic error rate with this last lesion. Here we report the case of a 19-year-old man with recurrent sacrococcygeal PS infection associated with an indurated dome-shaped blue-black nodule 1.7 cm in diameter. Clinical diagnosis of the nodule was uncertain suggesting a pigmentary or a vascular tumor. A complete resection of the two lesions was achieved. Pathological study showed a CBN showing a predominantly alveolar pattern associated with a chronic pilonidal disease. The tumor cells showed diffuse strong reactivity for melan-A and HMB-45, and focal reactivity for S-100 protein. Staining for Ki-67 (MIB1) was virtually negative. Differential diagnoses included atypical CBN, borderline melanocytic tumor and malignant melanoma. Radical excision provides a good prognosis for the rare association consisting of a common disease such as PS with the uncommon CBN.

Intraoral cellular blue nevus: report of a unique histopathologic entity and review of the literature.Cutis. 2007 Sep;80(3):189-92.

The blue nevus is found most frequently on the skin; however, in rare instances, it has been reported on oral mucous membranes. Intramucosal nevi make up more than one half of all reported intraoral melanocytic nevi. The common blue nevus is the second most common variant. Among the 3 variants of blue nevi, the cellular variant occurs less frequently than the common and combined variants. We present a rare case of intraoral cellular blue nevus that occurred on the oral mucosa of the hard palate. Because of the clinical and microscopic resemblance of the cellular blue nevus to melanoma and the rarity of this lesion in the oral cavity, recognition and accurate diagnosis are critical.