LAUSR

There is evidence for the usefulness of a swine animal model for teaching purposes in embolotherapy because of the similarity between human and pig anatomy. However, there is a permanent debate in biomedical research concerning the reproducibility of animal models and their applicability to human models. I read the article by Tradi et al. published in this issue of CVIR with great interest [1]. In this recently-published laboratory study conducted in 2016, the authors investigated the outcomes of healthy upper rectal artery embolisation in a swine model using three types of embolic agents. Despite interesting results, it is necessary to highlight that haemorrhoidal disease does not occur in swine. Transarterial embolisation is a leading therapy for gastrointestinal bleeding (GIB). It is indicated for acute focal GIB that causes haemodynamic deterioration and during impossible or failed endoscopy [2]. The anorectal region has a wide network of collateral circulation that permits the occlusion of superior rectal arteries (SRAs), without the risk of severe ischaemia. Considering this peculiarity, a novel indication has emerged since the last 8 years for the treatment of grade II-III haemorrhoids in patients with chronic and recurrent rectal bleeding, without haemodynamic deterioration [2, 3]. Emborrhoid is the colloquial term for SRA embolisation in case of chronic rectal bleeding secondary to internal haemorrhoids. Several studies have attempted to confirm the effectiveness of emborrhoid; however, there is no robust level of evidence [4]. As an emergent therapy, researchers have described several variations of this technique. There are no evidences for an optimal embolic agent and the endpoint of embolisation. Clinicians should consider the degree of haemorrhoid, the calibre of the SRA, flow velocity, coagulation status, and previous local treatments. Taken together, the expertise and preference of each IR will help selecting the embolic agent and the embolisation endpoint for particular case, according to their best criteria. Tradi et al. created random groups of three pigs each that were embolised with the SRA using 2 mm non-fibrated platinum microcoils (control group), with 500 l microspheres and 8% ethylene vinyl alcohol copolymer (EVOH). These pigs were euthanised 7 days post-embolisation, and the researchers performed gross and histopathological analyses of the anorectal region. The microcoil group revealed SRA recanalisation, the microspheres group revealed the absence of recanalisation without rectal ischaemia, whereas the EVOH group revealed the absence of recanalisation with signs of rectal ischaemia. According to the aforementioned data, EVOH would be dangerous for SRA embolisation. However, clinical experience in humans demonstrates the effectiveness and safety of EVOH for the embolisation of massive rectal bleeding, similar to coils with a lower rebleeding rate [5]. Tissue adhesives and EVOH are one of the standard embolic agents for the treatment of GIB owing to their high haemostatic power (Fig. 1). In contrast, Tradi et al. mentioned that the microspheres caused perineal cellulitis in one of the animals (33%). This complication may also occur in humans. & Jose Urbano [email protected]; [email protected]