Pathologic quiz case: paratesticular mass in a young man. Inflammatory myofibroblastic tumor of the paratestis.
A 36-year-old African American man presented with a 2-year history of a gradually enlarging right scrotal mass. There was no prior history of local trauma or pertinent medical history. He reported a family history of colon cancer. Physical examination revealed a firm testicular mass and right inguinal lymphadenopathy. Sonography showed an extratesticular, irregularly lobulated mass that measured 4.4 cm in diameter located adjacent to the right testis. The mass demonstrated heterogeneous echogenicity and hyperemic vascularity (Figure 1: thin arrow, tumor; thick arrow, normal testis). Moderate hydrocele was also noted. The left testis appeared unremarkable. Metastatic workup demonstrated no other lesions in the body. Serum α-fetoprotein and β-human chorionic gonadotropin levels were not elevated.A radical orchiectomy was performed. On bisecting the specimen, a circumscribed, firm, tan-white, 5 × 4 × 4-cm mass was seen adjacent to an uninvolved testis (Figure 2: thin arrow, tumor; thick arrow, normal testis). There was an associated hydrocele. No hemorrhage or necrosis was seen. Histologic sections showed an ill-defined and heterogeneous tumor of moderate cellularity arising in the tunica and merging with the hydrocele wall (Figure 3). The neoplastic cells were spindle-shaped to oval and had vesicular nuclei and eosinophilic cytoplasm (Figure 4). Tumor cells were embedded in a loose collagenous stroma. Rare mitotic figures, prominent vasculature, and a moderate infiltrate of lymphocytes, mast cells, eosinophils, and occasional plasma cells were present (Figure 4). Most tumor cells showed immunoreactivity for vimentin and focal immunoreactivity for smooth muscle actin. They were negative for cytokeratins (AE1/AE3), muscle-specific actin, desmin, CD34, anaplastic lymphoma kinase, and inhibin. Ki-67 labeled fewer than 5% of the tumor cells.What is your diagnosis?Inflammatory myofibroblastic tumor (IMT) has been described in the literature under a variety of names, including inflammatory pseudotumor, atypical myofibroblastic tumor, pseudosarcomatous myofibroblastic proliferation, pseudosarcoma, plasma cell granuloma, and proliferative funiculitis.1 Inflammatory myofibroblastic tumor occurs mainly in children and young adults, and is often mistaken for a malignant tumor. These tumors can involve many organs, with the urinary bladder being the most common site.1 Only a few cases of IMT have been reported in the paratestis (the spermatic cord, epididymis, and testicular tunics), most of which involved the spermatic cord.2 Paratesticular IMT may be associated with hydrocele and/or hematocele.Most paratesticular IMTs are ill-defined, nodular, gray- white, and firm. Cystic change or hemorrhage are rarely seen. The lesions are generally less than 3 cm in maximum dimension.2 They are tumors of myofibroblasts, with a spindle cell proliferation of variable cellularity seen in a background of loose collagenous to myxoid stroma, granulation tissue–type vascularity, and mixed inflammatory infiltrate. Some lesions may exhibit hyaline fibrosis of blood vessel walls. Three basic histologic patterns have been observed: (1) nodular fasciitis–like, (2) fibromatosis or fibrous histiocytoma–like, and (3) scarlike. The tumor cells have oval to spindle-shaped nuclei with vesicular chromatin, variably sized nucleoli, and eosinophilic to amphophilic cytoplasm. Cytologic atypia, nuclear pleomorphism, and mitotic figures are not prominent.The tumor cells are immunoreactive for vimentin and muscle markers, including muscle-specific actin, smooth muscle actin, and desmin. Occasional cells may stain for cytokeratin or epithelial membrane antigen. They are invariably negative for myoglobin and S100 protein.3 Immunohistochemical cytoplasmic positivity for anaplastic lymphoma kinase has been detected in these tumors at other sites and corresponds with the chromosomal rearrangement involving 2p23.1 Ultrastructurally, the tumor cells show features of myofibroblasts—bipolar cytoplasmic processes containing abundant rough endoplasmic reticulum and peripheral bundles of thin filaments with focal densities.4The exact etiology of IMT is unknown, although it is generally regarded as an exuberant reparative process. Chronic irritation, infection, and ischemia have been postulated as the primary insults.5 Retrospective flow cytometric study of urinary inflammatory pseudotumor has shown a diploid DNA content in most cases, further supporting the theory of benignancy of these lesions.6 However, some lesions occurring in the retroperitoneum, mesentery, mediastinum, and peritoneal surfaces of the endometrial cavity can recur and are potentially malignant.7 This putative neoplastic nature of IMT is supported by a translocation between chromosomes 2 and 9.1The differential diagnosis of paratesticular IMT includes inflammatory as well as neoplastic processes of the testis and epididymis. Fibrous pseudotumor would have a predominantly dense collagenous appearance. Other benign conditions resulting in a scrotal mass, such as testicular torsion, spermatocele, varicocele, or tuberculosis, must be ruled out. A panel of immunostains may be required to exclude myxoid leiomyosarcoma, rhabdomyosarcoma, sarcomatoid carcinoma, inflammatory fibrosarcoma, inflammatory liposarcoma, and malignant fibrous histiocytoma from the differential diagnosis.Complete surgical excision is the treatment of choice for paratesticular IMT. The prognosis is generally excellent; however, the clinical course may be variable, with well- encapsulated lesions showing regression or no tendency to progress. Some tumors may recur when resection is incomplete. Other therapeutic options, such as radiotherapy, methotrexate, or corticosteroids, have been used in patients with recurrent IMT.5
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