Pilonidal sinus associated with cellular blue nevus. A previously unrecognized association

• Published in: Journal of cutaneous pathology Vol. 34; no. 12; pp. 942 - 945
• Main Authors: Val‐Bernal, José Fernando, González‐Vela, María Carmen, Hermana, Sandra, Garijo, María Francisca, González‐López, Marcos A.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.12.2007; Blackwell
• Subjects: Adult; Biological and medical sciences; Dermatology; Diagnosis, Differential; Humans; Immunohistochemistry; Male; Medical sciences; Melanoma - pathology; Nevus, Blue - complications; Nevus, Blue - metabolism; Nevus, Blue - pathology; Pilonidal Sinus - complications; Pilonidal Sinus - metabolism; Pilonidal Sinus - pathology; Skin Neoplasms - complications; Skin Neoplasms - metabolism; Skin Neoplasms - pathology; Tumors of the skin and soft tissue. Premalignant lesions; Skin disease; Anatomic pathology; Blue nevus; Association; Dermatology; Pilonidal cyst; Benign neoplasm; Cell
• ISSN: 0303-6987; 1600-0560
• DOI: 10.1111/j.1600-0560.2007.00753.x

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.