Papillary thyroid carcinoma mistaken for malignant melanoma: pitfalls in diagnosis.

Abstract

Immunohistochemical methods and aspiration cytology are used with increasing frequency in the diagnosis of head and neck histopathology. Magnetic resonance imaging is also gaining popularity as a diagnostic tool. We report a case of papillary thyroid carcinoma which was initially misdiagnosed as malignant melanoma due to several confounding diagnostic test results. False-positive immunostaining of a cytologic preparation with a commercial preparation of HMB45 melanoma stain and characteristic MRI findings contributed to the erroneous diagnosis of malignant melanoma. Potential pitfalls in test interpretation are discussed, and recommendations for the judicious use of immunostaining, MRI, and other diagnostic studies are presented.