Enlarging aneurysm sac post EVAR – type V or occult type II Endoleak?

PURPOSE: Several theories exist regarding the underlying mechanism of type V endoleaks (T5EL), which remains unclear. Torikai et al. (2018) describe sac expansion in cases with patchy heterogenous enhancement of peripheral thrombus and postulate these are due to atypical type II endoleaks (T2EL) from proliferated vasa vasora. These cases of apparent endotension pose a therapeutic challenge as continued sac expansion warrants active intervention. MATERIALS AND METHODS: Retrospective review of T5EL cases was performed who underwent multidisciplinary discussion at our institution between 2020–2021. Clinical history and imaging were reviewed by a vascular interventional radiologist aiming to identify the underlying mechanism of sac expansion. RESULTS: Two cases of these specific T5ELs were identified. One patient underwent endovascular management and image-guided aspiration of intra-sac fluid whilst another underwent open surgical ligation and sac plication. In both cases, fluid re-accumulated with re-expansion of the aneurysmal sac on follow-up. Careful review of CT imaging showed subtle foci of peripheral sac enhancement, suggestive of vasa vasora causing occult T2ELs. This was not visible on single phase CTA, super-selective angiography or cone beam CT. CONCLUSION: We identified two complex cases with unexplained sac expansion following EVAR suggestive of T2ELs from proliferated vasa vasora. Transcatheter embolisation of this network of vessels although challenging has been previously considered to stunt sac expansion. We suggest this phenomenon is under-diagnosed. Nevertheless, long-term surveillance is warranted as continued sac expansion risks changes in aneurysm morphology leading to potential loss of the proximal/distal seal zones.