What kind of treatment might be less effective for large AVMs due to aggressive collateral development?

The effectiveness of surgical ligation in treating large arteriovenous malformations (AVMs) may be compromised due to the presence of extensive collateral circulation that develops as a compensatory mechanism. When an AVM is large, the blood vessels surrounding it often adapt by creating additional pathways for blood flow. This collateral circulation can effectively divert blood away from the area being targeted for surgical ligation.

As a result, even if the main feeding vessels are ligated during the surgery, the persistent collateral vessels can continue to supply the AVM, thereby allowing it to maintain its blood flow and preventing the desired outcome of obliteration. In contrast, embolotherapy may be more effective in such cases, as it can be used to directly occlude these vessels selectively, thus potentially leading to better control of the abnormal vascular structure.

Medication therapy and external compression clothing do not directly address the structural issues of the AVM, and while they may help manage symptoms, they do not target the vascular connections that create the malformation. Therefore, these treatment modalities are less relevant in the context of large AVMs compounded by aggressive collateral development.