Myointimoma: A Rare Tumor of the Penis

Abstract

To the Editor: Myointimoma is a benign tumor that was first described by Fetsch et al1 in the year 2000. It is considered to be a rare tumor arising from the intima of the vessels of the corpora cavernosa of the penis, and has been included as a specific entity among the genitourinary tumors in the latest review by the World Health Organization in 2006. In our review of the literature using the term myointimoma, we found only 17 cases. Myointimoma is a tumor that is usually found at the level of the glans and corona of the penis and presents clinically as a palpable, asymptomatic nodule of variable size. It develops over a variable period of days or months (4 days to 6 months),2 but despite the fast rate of growth, it is not an aggressive tumor. It can occur at any age, with cases reported from 2 to 61 years.1 It is not related to a history of local trauma or to the presence or absence of circumcision or any concomitant disease (connective tissue diseases, diabetes mellitus, or other autoimmune disease). Histologically it is characterized by a multinodular, mesenchymal proliferation that arises from the corpus cavernosum of the penis. The microscopic features that enable the diagnosis to be reached include the presence of a layer of spindle cells with a stellate pattern and with eosinophilic cytoplasm, set in a fibromyxoid matrix. It is situated in an intravascular position, in the form of nodules that occupy the endothelial lumen. There is no appreciable inflammatory infiltrate and mitoses are uncommon; there is no necrosis. Bundles of smooth muscle cells are observed at the periphery of the tumor. Although not essential for diagnosis of the tumor, immunohistochemical analysis can help in the differential diagnosis with other tumors of similar presentation. Cells are positive for a-smooth muscle actin, vimentin, and desmin (myoid origin) and negative for S-100 (melanocytic), CD34, CD31, epithelial membrane antigen, and factor VIII (endothelial origin). The peripheral stroma of the nodules is positive for CD34, CD31, neuron-specific enolase, and factor VIII antigen. Special stains, such as van Gieson stain, reveal abundant elastic fibers surrounding the nodular structures.1,2 Although tumors of the glans are usually rare, the differential diagnosis does include other tumors that present clinically as asymptomatic nodules, and that require histological differentiation from myointimoma.3,4 In particular, these other tumors include myofibroma, nodular fasciitis, leiomyoma, plexiform schwannoma, nerve sheath myxoma, and plexiform fibrohistiocytic tumor. Of all these, myofibroma is the main diagnosis to be considered, as many authors believe myointimoma to be a form of myofibroma, though arising exclusively in the penis, occupying the lumen of a vessel of the corpora cavernosa; these tumors are histologically identical and have a similar immunohistochemical pattern.4 The treatment of choice is surgical excision, though, given the tendency to remain stable and even to undergo involution, conservative management is chosen in the majority of cases. In the series by Fetsch et al,1 8 cases underwent remission and only 1 persisted after several years of follow-up; of the 5 cases reported by McKenny,2 none recurred after excision, as was also found in the cases reported by Robbins5 and Vardar.6 We present the case of a 74-year-old man in whom the only past history of note was positive serology for hepatitis C virus and benign prostatic hypertrophy. He was seen for a hard, asymptomatic nodule that had appeared on the glans 4 months earlier. The patient referred no history of trauma. On physical examination, there was a palpable, well-defined nodule of less than 1 cm in diameter, situated on the right side of the glans, close to the coronal sulcus. The nodule was not visible. The skin surface and color were unchanged and there were no signs of inflammation and no accompanying symptoms. Histopathological study revealed histological changes diagnostic of myointimoma (nodular structures derived from the intima of the cavernous vessels, formed of elongated cells with no atypia or mitoses) (Figures 1 and 2). Due to the benign nature of the lesion, it was decided to perform outpatient follow-up. Ten months after the biopsy, the nodule was still present, with no structural changes, and it remained asymptomatic.