A 34-year-old man with painless right scrotal swelling, first noticed four months earlier, was admitted to our hospital. The patient had no history of scrotal trauma, voiding difficulty, other genitourinary diseases or weight loss. Physical examination showed that the right side of the scrotum was noticeably enlarged, without tenderness. Laboratory studies were unremarkable, with normal levels of alpha-fetoprotein (1.70 ng/ml; normal range: < 20 ng/ml) and beta-human chorionic gonadotropin (3.42 mIU/nl; normal range: < 5 mIU/nl). Under the impression of right epididymo-orchitis, he was treated with antibiotics for two weeks but showed no improvement.

Scrotal US revealed a well-defined heterogeneous hypoechoic intratesticular lesion of the right testis, with large hydrocele and diffuse irregular epididymal swelling. Also noted were slightly heterogeneous echogenic nodular projections attached to the inner scrotal wall (Fig. 1A). The left testis and epididymis were normal. For further evaluation, MR imaging was performed, and this demonstrated nodules in the testis, epididymis and inner scrotal wall. The nodules were isointense on T1-weighted images and slightly hyperintense on T2-weighted images. T2-weighted imaging of the intratesticular lesion revealed a low-signal-intensity rim. After infusion of gadopentetate dimeglumine (Gd) (Magnevist; Berlex, Wayne, N.J., U.S.A.), the peripheral portions of these nodules were markedly enhanced (Fig. 1B-E).

Because malignancy was suspected, the patient underwent right radical orchiectomy, and right hydrocele with testis was dissected out without difficulty. On pathologic examination of the resected specimen, variable-sized multiple nodules were seen on the surface of the tunica vaginalis and albuginea; the largest one was attached to the posterolateral portion of the testis. Microscopic examination revealed that the nodules were confined to the tunica vaginalis and albuginea, without penetrating the testis, and between this and the nodules there was a clear plane of separation (Fig. 1F). The testis and epididymis were normal. The tumor cells were oval, or round to elongated, with occasional longitudinal nuclear grooves and Call-Exner bodies, and mitosis was frequently observed (nine mitoses/ten high-power fields, on average). Immunohistochemical staining demonstrated diffuse strong positivity for inhibin, vimentin and cytokeratin. A comparison of the microscopic findings and those of MR imaging indicated that the hypointense rim seen at the periphery of the nodules on T2-weighted images corresponded with intact tunica albuginea.

Although granulosa cell tumor is the most common sexcord stromal tumor to occur in the ovary, it is extremely rare in the testis and its origin is poorly understood. To the best of our knowledge, the literature in English is limited to only 19 cases of adult granulosa cell tumor of the testis (10). Moreover, the radiologic findings of this disease entity are not well known. We are aware of only two previous reports of the US findings of adult-type testicular granulosa cell tumor, and both of these described the tumor as a well-defined hypoechoic testicular mass (11, 12).

In our case, the tumor appeared to arise from the scrotal tunics, an unusual location for a sex-cord stromal tumor. It was, however, because of the presence of typical large indented nuclei with longitudinal nuclear grooves and Call-Exner bodies, as well as positive immunoreactivity for inhibin, keratin and vimentin, that granulosa cell tumor was diagnosed (13). Fourteen percent of all paratesticular tumors arise from the scrotal tunics and among these, benign fibroma, representing a fibrous reaction to chronic periorchitis, is the most common lesion (14). Although granulosa cell tumor arising from the scrotal tunics has not been previously reported, extratesticular sex-cord stromal tumor in the pelvis has been described (9). The suggested explanation is that the tumor originated in a residual part of the primitive gonad or a third undescended testis which was completely destroyed by the process, and we believe that in our case the same explanation is possible.

Pathologic examination indicated that this tumor had originated from and was confined to the scrotal tunics. The testis and epididymis were normal and easily separated from the tumor. Nevertheless, because the largest nodule was deeply invaginated into the testis, displacing the epididymis, which was compressed and not visualized, the location of this tumor - according to the findings of US and MR imaging - was intratesticular and epididymal. It was because the main lesion was in the testis and epididymis, and multiple small nodules were attached to the inner scrotal wall, that malignancy was suspected. On the other hand, because of extensive hydrocele, the lesion also mimicked an inflammatory condition such as tuberculous epididymo-orchitis. The only clue to the origin of the mass was the low-signal-intensity rim between the lesion and the testis revealed by T2-weighted imaging.

To our knowledge, this is the first reported case of paratesticular granulosa cell tumor, and it would therefore be premature to state that the US and MR features of our case are specific to granulosa cell tumor of the scrotal tunics. Although the formulation of a treatment plan might not require specific diagnosis, we suggest that the presence of a mass seen as an intratesticular lesion associated with multiple enhancing nodules attached to scrotal tunics indicates the possibility of a paratesticular tumor, and that granulosa cell tumor should be included in the differential diagnosis. We believe that MR imaging findings of a peripheral low-signal-intensity rim on a T2-weighted image might help determine the origin of the mass.