title: Pilonidal sinus associated with cellular blue nevus. A previously unrecognized association.
abstract: 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.
authors.affiliation: Department of Anatomical Pathology, Marqués de Valdecilla University Hospital, Medical Faculty, University of Cantabria, Santander, Spain. apavbj@humv.es
authors.forename: José Fernando
authors.initials: JF
authors.lastname: Val-Bernal
authors.forename: María Carmen
authors.initials: MC
authors.lastname: González-Vela
authors.forename: Sandra
authors.initials: S
authors.lastname: Hermana
authors.forename: María Francisca
authors.initials: MF
authors.lastname: Garijo
authors.forename: Marcos A
authors.initials: MA
authors.lastname: González-López
mesh_terms: D000328:Adult; D003937:Diagnosis, Differential; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008545:Melanoma / Q000473:pathology; D018329:Nevus, Blue / Q000150:complications* / Q000378:metabolism / Q000473:pathology; D010864:Pilonidal Sinus / Q000150:complications* / Q000378:metabolism / Q000473:pathology; D012878:Skin Neoplasms / Q000150:complications* / Q000378:metabolism / Q000473:pathology