Highly Vascularized Scars in Cases of Regressed Testicular Germ Cell Tumors: An Occasional Mimic of Hemangioma and a Diagnostic Pitfall.

We identified 34 cases of regressed testicular germ cell tumors with highly vascularized scars; in 4 cases, the blood vessels were so prominent that hemangioma rather than germ cell tumor regression was considered, a misinterpretation that could result in clinical mismanagement since patients with regressed germ cell tumors require evaluation for metastases and, at a minimum, surveillance. The patients were 16 to 67 years old (median, 37) and usually presented with masses or metastases. Eleven of 12 cases of partial regression had a seminoma component, and seminoma was found in 5 of 7 different cases with sampled metastases. On microscopic examination, the cases usually showed numerous small blood vessels and a variably prominent lymphoplasmacytic infiltrate within scars, often with the greatest vessel concentration at the scar periphery. In 4 cases, a diffuse pattern of numerous, closely packed, small, round or slit-like vessels in fibrous stroma simulated hemangiomas, but with a lymphocyte-rich background. Quantification of the vessel concentration within the scar in the 30 cases where hemangioma was not mimicked showed an average increase in vessel density of 2.6 (range: 1.2 to 8.0) over non-neoplastic parenchyma. For the 4 "hemangiomatoid" cases, this ratio exceeded 6. The testis surrounding the scars showed, in all cases, the atrophic changes common to testes harboring germ cell neoplasia in situ-derived germ cell tumors. We conclude that highly vascularized testicular scars caused by regression of testicular germ cell tumors can occasionally show such a high concentration of blood vessels that they mimic hemangiomas. Seminoma is the most common germ cell tumor type to induce this florid reaction. Recognition of this phenomenon is important for proper clinical management.