Microscopic description:

The tumor is composed of an anastomosing proliferation of capillary sized vessels, remniscent of splenic sinusoids (but without white pulp) with absent mitotic activity and mild endothelial nuclear variability. No adrenal tissue is identified.

CD31 highlights endothelial cells. Tumor is negative for Ae1/Ae3, inhibin and Melan A.

Based on microscopic features and IHC, the tumor shows features compatible with diagnosis of Anastomosing hemangioma.

Discussion:

Anastomosing hemangioma is a benign, vascular neoplasm first described in kidney.

Other involved areas include testis and the spermatic cord, the ovary, the adrenals, the liver, the colon, the small bowel and the mesentery, the bladder, the soft tissues especially in paraspinal location and the bones.

The lesion is usually discovered incidentally after imaging studies. Less frequently, hematuria and back pain in renal cases, or mass effect and local pain in non-renal cases.

On computed tomography imaging, it usually seems circumscribed, hyperdense or hypodense, and heterogenous. So the lesion is often underdiagnosed before surgery and is usually overtreated.

Grossly, it presents as a well-circumscribed, more frequently non-encapsulated, gray or red-brown colored lesion exhibiting a fleshy cut surface and spongy texture.

At low magnification, the tumor appears well circumscribed with diffuse growth pattern. Higher magnification shows irregular capillary-sized vascular spaces with a prominent anastomosing configuration, lined by a single layer of round to oval endothelial cells, exhibiting frequent hobnail morphology.

Anastomosing hemangiomas are often mistaken for well-differentiated angiosarcomas because of their anastomosing architecture, non-lobular growth pattern, and mild endothelial cell atypia, with “hobnail” endothelial cells.

Immunohistochemical studies show diffuse staining for endothelial markers, including CD31, CD34, factor VIII, ERG, and FLI1. Immunostaining for smooth muscle actin highlights supportive pericytic cells bordering the endothelial cells. Ki-67 staining indicates a low proliferative activity of the endothelial cells.

GLUT-1, CD8, and D2-40 immunostains are negative, suggesting that the tumor is not related to juvenile hemangioma (GLUT-1 positive) or splenic sinusoids (CD8 positive) and is not of lymphatic origin (D2-40 positive). The endothelial cells always lack immunoreactivity for human herpes virus-8 antigens, markers of Kaposi sarcoma. Epithelial markers including epithelial membrane antigen are absent.

Differential diagnosis:

Table describing Anastomosing hemangia

Anastomosing Hemangioma: Short Review of a Benign Mimicker of Angiosarcoma, Eleni Lappa, MD;Elias Drakos, MD, PhD. Arch Pathol Lab Med (2020) 144 (2): 240–244. https://doi.org/10.5858/arpa.2018-0264-RS

References:

John, Ivy MBBS; Folpe, Andrew L. MD Anastomosing Hemangiomas Arising in Unusual Locations, The American Journal of Surgical Pathology: August 2016 - Volume 40 - Issue 8 - p 1084-1089 doi: 10.1097/PAS.0000000000000627

Anastomosing Hemangioma: Short Review of a Benign Mimicker of Angiosarcoma Eleni Lappa, MD ;Elias Drakos, MD, PhD Arch Pathol Lab Med (2020) 144 (2): 240–24 https://doi.org/10.5858/arpa.2018-0264-RS

Montgomery E, Epstein JI. Anastomosing hemangioma of the genitourinary tract: a lesion mimicking angiosarcoma. Am J Surg Pathol. 2009 Sep;33(9):1364-9. doi: 10.1097/PAS.0b013e3181ad30a7. PMID: 19606014.

https://www.pathologyoutlines.com/topic/softtissueanastomosinghemangioma.html Authors: Ivy John, M.D., Lauren N. Stuart, M.D., M.B.A

CASE IMAGES