Leiomyomas are benign tumours of smooth muscle predominantly found in the uterus. Very rarely, they may arise from the dartos muscle of the scrotum. Scrotal leiomyomas are more common in Caucasians between the fourth and sixth decades of life as solitary painless cutaneous lesions measuring 1–14 cm with an average diameter of 6.4 cm . Typically, the patients present at an average of 7.6 years from onset of mass due to its slow growing and asymptomatic nature .
However, our case was a Negro who presented at 39 years of age with occasional pain. He presented within 1 year of recognition of mass because of the associated pain and fear of having a malignancy. The scrotal ultrasound scan suggested a mass which was attached to the testis with differential diagnoses of epidermoid cyst, germ cell tumour and adenomatoid tumour. This heightened a suspicion of a testicular tumour which necessitated a radical orchidectomy since most solid testicular masses are malignant. Magnetic resonance imaging (MRI) has been found to provide additional and important information to scrotal ultrasound in detection and localization of scrotal tumours as reported by Cassidy et al. . However, ultrasound is far cheaper and more readily available in our environment. Guthrie and Fowler found ultrasound to have 98% and 99.8% sensitivity and specificity, respectively, for testicular malignancy .
Benign smooth muscle tumours of the scrotum are classified either as typical or atypical leiomyoma. Four histologic criteria are used in this classification: (1) size ≥ 5 cm in widest diameter, (2) presence of infiltrating margins, (3) ≥ 5 mitotic figures per 10 high-power fields and (4) moderate cytological atypia. Those with any one of these features are described as typical while tumours with two features are atypical leiomyoma [3, 9, 10]. The occurrence of three or more of these features renders such a leiomyosarcoma. The index case is a typical leiomyoma, and the principal treatment is surgical excision.