Anastomosing Hemangiomas Arising in Unusual Locations: A Clinicopathologic Study of 17 Soft Tissue Cases Showing a Predilection for the Paraspinal Region.

Anastomosing hemangioma, a recently recognized benign vascular neoplasm originally described in the kidney, may be confused with well-differentiated angiosarcoma. Rare cases of anastomosing hemangiomas have been described in the liver and in nonrenal genitourinary sites. We report a series of 17 anastomosing hemangiomas occurring in unusual locations, in particular in the paravertebral soft tissues. The 17 tumors occurred in 10 male and 6 female patients, ranging in age from 2 to 85 years. One patient had bilateral, synchronous tumors involving the right paracaval and left para-aortic soft tissues. Thirteen (76%) cases involved the soft tissues near the vertebral column, including the paravertebral region (n=4), the psoas muscle (n=2), the costovertebral angle (n=2), para-aortic soft tissue (n=2), and the paracaval, parasacral, and retroperitoneal soft tissues (n=1 each). Other locations included the anterior mediastinum, uterine cornu, infundibular pelvic ligament, and upper arm (n=1 each). Imaging studies, available in 13 cases, were not felt to be diagnostic of a hemangioma. The tumors ranged from 1.5 to 7.5 cm (median, 3.6 cm) in size and were grossly well demarcated. All cases showed typical morphologic features of anastomosing hemangiomas, including a nonlobular architecture, an anastomosing proliferation of capillary-sized vessels with mild endothelial cell nuclear variability, scattered hobnailed endothelial cells, and small fibrin thrombi. Mitotic activity was rare or absent. Adipocytic metaplasia and extramedullary hematopoiesis were present in subsets of cases. When performed, immunohistochemical studies showed expression of endothelial markers (eg, CD31, CD34). In only 1 case did the submitting pathologist favor a diagnosis of anastomosing hemangioma; 4 cases were submitted specifically to exclude a well-differentiated angiosarcoma. Clinical follow-up available in 13 cases has not revealed any local recurrences or metastases. This series, the first formal description of anastomosing hemangiomas involving soft tissue locations, shows these tumors to have a notable predilection for the paraspinal region. The diagnosis of soft tissue anastomosing hemangioma may be challenging, as imaging studies do not show classical features of hemangioma and as these tumors may be sampled with limited needle biopsies. Awareness of this entity, and appreciation that they may occur in nongenitourinary sites, should allow its confident distinction from potentially more aggressive lesions, in particular angiosarcoma.