This video details the pathology and differential diagnosis of Anastomosing Hemangioma (AH), a rare, benign vascular neoplasm historically described in the genitourinary tract but also found in somatic soft tissues. The importance of AH lies in its microscopic resemblance to well-differentiated angiosarcoma due to its key feature: interconnected, capillary-sized vascular channels.
The presentation focuses on distinguishing AH from malignancy. Key distinguishing features include AH’s typically circumscribed (non-infiltrative) border, the presence of minimal or absent nuclear atypia and mitotic activity, and the lack of endothelial cell multi-layering. Common secondary findings that support an AH diagnosis include frequent thrombotic fibrin thrombi within vessel lumens, scattered mast cells, areas of sclerosis, and, in a subset of cases, extramedullary hematopoiesis (EMH). Finally, the video notes the molecular basis of the tumor, highlighting that a majority of tested cases harbor a GNAQ gene mutation.
Pathological Analysis of Anastomosing Hemangioma
0:03 Rare Vascular Neoplasm: Anastomosing Hemangioma (AH) is introduced as a rare vascular neoplasm, initially described in the genitourinary (GU) tract (kidneys). It is also found in somatic soft tissue, particularly the paravertebral/paraspinal region.
0:20 Mimics Angiosarcoma: The lesion is important because its anastomotic (interconnected) vascular channels mimic the aggressive pattern of well-differentiated angiosarcoma.
1:43 Key Differentiator: Circumscription: The most important feature distinguishing AH from angiosarcoma is that AH is typically a well-circumscribed lesion that "shells out" during surgery, lacking the infiltrative growth pattern of angiosarcoma.
3:06 Lack of Atypia: Despite the concerning anastomotic pattern, AH shows minimal nuclear atypia (small, generally uniform nuclei) and minimal or no mitotic activity.
4:41 Hobnailing: Endothelial cells often exhibit "hobnailing" (nuclei bulging into the vessel lumen). Key Takeaway: Hobnailing is a non-specific feature seen across many vascular lesions and is not diagnostic for AH.
5:22 Absence of Multilayering: AH lacks the multi-layering or "stacking" of endothelial cells—a highly worrisome finding characteristic of angiosarcoma. AH channels are lined by a single, thin layer.
3:37 & 6:16 Scattered Mast Cells: Mast cells are a common feature, sometimes appearing darkly stained due to prominent granules, which can be mistaken for large, atypical nuclei at low magnification.
7:41 Luminal Thrombi: Thrombotic fibrin thrombi filling the vessel lumens are a particularly striking and common finding in AH. DDx reminder: This feature must be distinguished from angiolipoma or Masson tumor.
10:14 Extramedullary Hematopoiesis (EMH): A subset of cases (including the example shown) features EMH, identified as small, dark, round red cell precursors. This is a supporting feature helpful for diagnosis.
12:28 Molecular Findings (GNAQ): The majority of tested AH cases have been found to harbor a GNAQ gene mutation. Key Takeaway: The GNAQ mutation is intriguing as it is also found in other congenital vascular lesions (e.g., Sturge-Weber syndrome) and non-vascular tumors (uveal melanomas), highlighting common molecular pathways across different tumor types.