Epididymis rhabdomyoma: A case report and literature review
© Han et al.; licensee BioMed Central Ltd. 2012
Received: 10 March 2012
Accepted: 20 April 2012
Published: 20 April 2012
Genital rhabdomyoma is very rare tumor that usually occurs in the vulvar of young women. Epididymis rhabdomyoma in a young man is extremely uncommon and has rarely been reported. Here, we report a case of epididymis rhabdomyoma of a 17-year-old man and review the literatures.
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Rhabdomyoma is an exceedingly rare benign tumor of striated muscle. It can be divided into the following categories: cardiac rhabdomyomas and extracardiac rhabdomyomas, which are relatively rare . Genital rhabdomyoma is even more uncommon, usually occurs in the vulva of young women [2, 3]. Epididymal rhabdomyoma is extremely rare in the world and has rarely been reported [4, 5]. Here, we report a case of epididymis rhabdomyoma of a 17-year-old man and review of the literatures.
A firm mass with tan white fibrous capsule measured 1.5cm1.0cm1.0cm in the head of epidymis (Figure1, A). The cut surface of the tumor was solid, tan-white, had a faint fascicular pattern (Figure1, B). No hemorrhage or necrosis was noted.
Histology and immunohistochemistry
The tumor was fixed in 10% formalin and embedded in paraffin. Several 4-m sections were cut from each paraffin block. Hematoxylin-eosin (HE) and immunohistochemical (IHC) stains were performed. IHC staining was performed using the streptavidin-peroxidase system (Ultrasensitive; MaiXin Inc., Fuzhou, China) according to the manufacturer's instruction. Commercially available prediluted monoclonal antibodies against the following antigens were employed: Actin (sm, smooth muscle) (1:200; Mouse mAb (DE-B-5), Merck), CK (1:200; Mouse mAb (B311.1), Merck), S-100 (1:200; Mouse mAb (1B2), Merck), CD34 (1:200; Mouse mAb (QBEnd/10), Merck), Vimentin (1:200; Mouse mAb (V-9), Merck), Desmin (1:200; Mouse mAb (DE-B-5), Merck) and Ki-67 (1:200; MIB1, Dako). The immune reactions were visualized with the use of DAB as the chromogen (Sigma-Aldrich Co, St Louis, Mo, USA). All internal and external controls worked appropriately.
Rhabdomyomas are benign tumors of striated muscle cells and generally divided into the following categories: cardiac rhabdomyomas, which are relatively common, and extracardiac rhabdomyomas (occurring outside of the heart), which are rare (comprising only 2% of all tumors with striated muscle differentiation) [2, 3]. Based on clinical manifestations and morphological characteristics, the extracardiac forms of rhabdomyoma are subclassified into 4 distinct types: (1) the fetal type, a rare form that affects the head and neck region but occurs in both children and adults. Within the fetal subtype, there is a wide spectrum of histology reflecting the degree of differentiation [7, 8]; (2) the adult type, usually found in the head and neck region of the older person and slowly growing, more than 40% recur. This type tumors can be multinodular, cells are rounder, and there are crystalline cytoplasmic inclusions of hypertrophic Z-band material [9–11]; (3) the genital type, a tumor-like polypoid or cystic mass that has been described commonly in the genital tract of middle-aged women with a mean age of 42years. This type resembled fetal rhabdomyomas in architecture but showed greater maturity of the myocytes [4, 12, 13]; and (4) rhabdomyomatous mesenchymal hamartomas, a peculiar striated muscle proliferation that occurs chiefly in the periorbital and perianal region of infants and young children. The pathologic subtype does not necessarily reflect the age of the patient.
The differential diagnosis of an epididymal tumor includes TB, spermatic granuloma, adenomatoid tumor (a common tumor in this location), mesothelioma, papillary cystadenoma (especially if the patient has a family history of von Hippel-Lindau disease), and embryonal rhabdomyosarcoma. The right epididymal tumor removed from the young patient showed clinicopathologic features typical of the genital variant of extracardiac rhabdomyoma. Additional histologic considerations consist of other benign processes, such as leiomyoma and fibromatosis; the presence of cross-striations and IHC steins rule out leiomyoma or fibromatosis. Histologically, the fetal variant of rhabdomyoma shares many features of the genital variant, and usually has a more myxoid and less collagenous stroma with proliferation of immature mesenchymal cells and is more cellular. Embryonal rhabdomyosarcoma should be considered in the differential diagnosis, in which one would expect to find necrosis, increased mitotic activity, abnormal mitoses, nuclear atypia, pleomorphism, anaplasia and a high proliferation index, e.g. Ki67>5% .
Here, we report this quite rare tumor and provide comprehensive figures, including gross appearance, HE and IHC staining. This is the third epididymal rhabdomyoma described in the English literature [4, 5]. The first two cases are both 20years old. They did not present specific symptoms, and a tumor mass in left epididymis (5.5cm4.0cm2.5cm and 5.0cm4.0cm2.0cm respectively) was the only finding. The probable origin is the cremaster muscle. Additionally, there are other six rhabdomyomas in the male genitourinary tract described in English, two in the spermatic cord (67-year-old man, 3.0cm2.0cm2.0cm,17-year-old man, 3.5cm2.4cm2.1cm, respectively) [10, 15], one in the tunica vaginalis (19-year-old man) , one in prostate (nineteen-year-old white man)  and two paratesticular (10months of infant, 1.5cm and 55-year-old man, 6.0cm5.5cm4.5cm, respectively) [17, 18]. When faced with a pleomorphic mesenchymal tumor in the male genitourinary tract, pathologists should remember the diagnosis of rhabdomyoma. To our knowledge, rhabdomyomas exhibited benign behavior and low recurrence rate in other sites. Further documentation and follow-up of such cases will help better define the biological behavior and prognosis of the rhabdomyomas.
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