IMHMV has classically been reported in otherwise healthy young to middle-aged men, although recent cases, including this one, have identified the disease in females or older patients (Platz 2012). Clinical diagnosis of IMHMV is difficult and generally ascertained via histopathology after surgical resection (Platz 2012; Yun et al. 2016). Patients present with nonspecific symptoms that mimic IBD, including severe abdominal pain, weight loss, rectal bleeding, and diarrhea or constipation (Song and Shroff 2017). Patients may also present with subtle bowel perforations (Almumtin et al. 2021). Initial radiologic evaluation of IMHMV patients may yield findings suggestive of colitis, and endoscopy can produce nonspecific inflammatory findings, both of which were seen in this patient.
Patients typically undergo a protracted clinical course of colitis that ultimately requires surgical resection. This patient is unique as her colitis was thought to be secondary to an abnormal arteriovenous connection, which was discovered on conventional angiography performed during mesenteric ischemia work-up.
While uncommon, mesenteric arteriovenous anomalies are well-documented, with multiple case reports describing successful endovascular embolization of arteriovenous fistulas and malformations (Hendy et al. 2018; Hussein 2013; Athanasiou et al. 2014). Endovascular embolization is less invasive and presents fewer complications in comparison to surgical resection, although it does carry potential for bowel ischemia (Hussein 2013). Since only partial embolization was achieved in this case, the interventional radiology team acknowledged the possibility that pain would return as new arterial feeders develop post-embolization and repressurize the venous system. The patient did see significant pain reduction, and her opioid requirement decreased in the subsequent days, but this relief was transient, lasting only 11 days. This certainly raises the possibility of a placebo effect from embolization or temporary improvement from perioperative pain killers. Additionally, it is possible this patient’s abnormal arteriovenous connection may not have represented a true primary arteriovenous malformation (AVM), but a secondary, nonspecific arteriovenous connection associated with either IMHMV and/or chronic thrombosis of the IMV.
The definitive etiologies of both mesenteric AVM and IMHMV are unknown. It is plausible that AVM and IMHMV are associated, but no previous studies have proven the basis of this association. IMHMV is characterized by smooth muscle proliferation in small and medium-sized mesenteric veins, in essence creating venous arterialization that leads to stenosis and possible occlusion. Thus, prior reports have hypothesized that IMHMV results from an arteriovenous connection that leads to increased pressurization of the veins, resulting in venous arterialization.
Standard treatment for both IMHMV and AVM is surgical resection of the affected section of bowel. The median time from patient presentation and symptom onset to surgical resection is 5 months. However, endovascular embolization has also been shown to be a viable treatment option for arteriovenous connections where the anatomy is amenable. There have not yet been any reports of successful conservative medical treatment for IMHMV. Typically, the diagnosis is missed, and surgery is performed after significant morbidity or failure to respond to IBD medical treatments (Bronswijk et al. 2019).
This case illustrates the possible significance of an arteriovenous connection in the setting of ischemic colitis with a plausible pathogenic relationship with IMHMV. Coupling this case with the previously hypothesized associations with vascular anomalies, early radiologic evaluation for an abnormal arteriovenous connection may facilitate a diagnosis of IMHMV. While embolization did not yield long-term benefit in the presented case, further study is needed to investigate the utility of endovascular approaches as a viable treatment alternative to resection for IMHMV with an abnormal arteriovenous connection, particularly when diagnosed early, as endovascular treatment offers significant benefits (Hendy et al. 2018). Earlier IMHMV identification may also yield earlier diagnosis and improved outcomes for patients with neuroendocrine tumors, which have been shown to be associated with this condition (Guadagno et al. 2016). With increased awareness of the condition, IMHMV can be considered in the differential diagnoses of patients presenting with protracted severe abdominal pain and colitis without a clear infectious or inflammatory etiology.