US of the Tunica Vaginalis Testis: Anatomic Relationships and Pathologic Conditions1

Extratesticular lesions are common incidental findings at ultrasonography (US) among men and boys. Most lesions originate from or depend on the tunica vaginalis, a mesothelium-lined sac with a visceral layer and a parietal layer. The tunica vaginalis is formed when the superior portion of the processus vaginalis closes during embryologic development. Abnormal closure of the processus vaginalis leads to congenital anomalies of the tunica vaginalis, such as complete or partial patency of the processus vaginalis, spermatic cord hydrocele, and inguinoscrotal hernia. The proximity of the visceral layer to the testis explains the reactive involvement seen in epididymo-orchitis, with resultant pyocele or abscess formation. The tunica vaginalis also may be affected by inflammatory and traumatic disorders such as scrotal calculi, fibrous pseudotumor, or hematocele. These lesions manifest as solid or heterogeneous tumorlike masses. Lesions of mesothelial origin, such as adenomatoid tumor, tunica cyst, and mesothelioma, may involve the tunica vaginalis. Entrapped mesenchymal cells can lead to lipoma, leiomyoma, or sarcoma, although these tumors are uncommon in the tunica vaginalis. US is not useful for differentiating between benign and malignant tumors; however, some characteristic findings may help in planning the best surgical approach. Knowledge of the embryologic development, anatomic relationships, and pathologic disorders of the tunica vaginalis is essential to narrow the differential diagnosis of an extratesticular lesion. In most cases, US findings in combination with clinical assessment can indicate whether nonsurgical management or testis-sparing surgery is warranted.