Aneurysm formation in an angiomyolipoma during bevacizumab combination therapy

) in association with chemo-therapeutic agents has become a standard treat-ment for patients with metastatic colorectal cancer reaching a median overall survival of 22.7 months [1]. However, bevacizumab-therapy can be associ-ated with some adverse events, including bleeding (3%), gastrointestinal perforation (2%), arterial thromboembolism (1%), hypertension (5.3%), pro-teinuria (1%) and wound-healing complications (1%) [2–5]. Bleeding complications have been observed as pulmonary hemorrhage and/or hemop-tysis, mainly in patients with lung cancer; gingival and vaginal bleeding have also been reported, but are less common [2]. Herein, the occurrence of a (pseudo-)aneurysm within an asymptomatic renal angiomyolipoma in a patient with colorectal liver metastases treated with FOLFIRI and bevacizumab is reported. A 57-year-old woman underwent a laparoscopic low anterior resection for obstructing rectosigmoid carcinoma with concommitant diffuse liver metasta-ses. At pre-operative screening CT, a fat-containing mass lesion was detected suggestive of an angiomyo-lipoma (Figure 1). A true-cut biopsy of the renal lesion was performed. Pathological analysis confi rmed the diagnosis of an angiomyolipoma. One month postoperatively, chemotherapeutic treatment with FOLFIRI and buvacizumab was started to manage the liver metastases. Control CT-scan three months after start of the chemotherapeutic treatment showed a marked involution of the liver metastases, but also a (pseudo-) aneurysm within the angiomyolipoma. The (pseudo-) aneurysm had a diameter of 4.5 cm with peripheral thrombus-formation (Figure 2). It was agreed to exclude the (pseudo-)aneurysm by transcatheter embolization. Under local anesthesia, the feeding vessel was selectively catheterized (Figure 3a) and occluded by 250 μ microparticles (Embozene, CeloNova, Newnan, GA, USA) and microcoils (Microtornado, Cook Medical, Bjaeverskov, Den-mark) (Figure 3b). FU-CT two months later depicted a further shrinkage of the liver metastases and a full exclusion of the (pseudo-) aneurysm. Bleeding complications associated with bevaci-zumab-therapy potentially can be explained by the anti-angiogenic effect, thus inhibiting the growth of the endothelium which might result in vessel wall contiguity and pseudoaneurysm formation. In the present case, the exact pathophysiological mechanism for the development of the (pseudo-)aneurysm within the angiomyolipoma is not very clear. A vessel wall lesion might be induced initially by the true-cut biopsy. However, FU-CT one month after the biopsy showed no radiological sign of intralesional aneurysm formation. Bevaci-zumab therapy might have jeopardized endotheli-alization at a biopsy-injured vessel, a phenomenon which is similar to late bevacizumab-related surgi-cal site complications [6]. Also, bevacizumab ther-apy might have a direct effect on the physiology of the endothelium of the vascular components of the angiomyolipoma. Angiomyolipoma may harbor subtle microaneurysms not visible on imaging and a pseudoaneurysm may have developed spontane-ously at the site of such a microaneurysm with a susceptible and fragile endothelial lining [7].