S3878 Preoperative Diagnosis of Idiopathic Myointimal Hyperplasia of the Mesenteric Veins (IMHMV) in a Post–Liver Transplant Patient

Introduction: Idiopathic myointimal hyperplasia of the mesenteric veins (IMHMV) is an exceedingly rare non-thrombotic, non-inflammatory cause of ischemic colitis, characterized by luminal obliteration of medium to large-sized mesenteric veins by proliferating smooth muscle cells and myofibroblasts embedded in a myxoid matrix, that is often clinically misdiagnosed as inflammatory bowel disease (IBD) or infectious colitis. It is typically diagnosed following surgical resection via full-thickness histology, and as a result is often a delayed diagnosis, generally preceded by prolonged hospitalization and failed medical therapies. This case represents a rare instance in which the histologic diagnosis of IMHMV was made preoperatively. Case Description/Methods: A 41-year-old woman with alcohol-associated cirrhosis status-post deceased donor liver transplant 1.5 years ago presented with worsening diffuse abdominal pain, non-bloody diarrhea, anorexia, and nausea for 2 months. Labs revealed hemoglobin 8 (baseline 14) g/dL, C-reactive protein 12 mg/L, Clostridioides difficile PCR (+)/toxin assay (-). Serial cross-sectional imaging showed progressive left-sided colitis with proximal distension. The patient underwent 5 total lower endoscopies, notable for severe sigmoidal inflammation/focal stricture with transverse colon and rectal sparing. She received extended antibiotic therapy against C. difficile as well as 2 fecal microbiota transplantations without clinical improvement. The third lower endoscopy yielded adequate tissue sample for histologic examination revealing ischemic changes with pseudomembranes, remodeling of lamina propria capillaries with arteriolarization, circumferential subendothelial fibrin deposits, and intravascular thrombi consistent with venous hypertension secondary to IMHMV. Bacterial peritonitis (secondary to a contained colonic perforation) was diagnosed on hospital day 29 and treated uneventfully with piperacillin-tazobactam. On hospital day 44, the patient underwent hemicolectomy with examination of the resected specimen confirming the diagnosis of IMHMV. The patient clinically improved without complication and was discharged on hospital day 53. Discussion: IMHMV may be confounded by or mistaken for infections like C. difficile and may clinically mimic IBD. Surgical resection is curative, however delays to surgery of up to 6 months or longer have been reported. Early preoperative diagnosis of IMHMV may reduce unnecessary therapies and decrease time to surgery as definitive treatment.