Popliteal artery aneurysmal dilatation by intimomedial mucoid degeneration causing emergency limb ischemia: a case report and literature review

Intimomedial mucoid degeneration (IMMD) is an extremely rare vascular condition characterized by mucin accumulation in the intima and media, resulting in arterial wall elastic tissue degradation and aneurysm formation. We report the case of a 34-yearold woman who presented to the emergency department with a 1-month history of left lower limb pain. On local physical examination, both lower limbs were warm with palpable regular pulses in the entire lower limbs and normally capillary refill. No palpable masses were felt. Computed tomography angiography (CTA) of the lower limbs revealed an aneurysm with a thrombosed sac in the left popliteal artery behind the knee joint. Thoracic and abdominal CTA revealed normal findings. The patient underwent posterior exploration of the left popliteal artery, which revealed a large aneurysm requiring excision, and an interposition vein graft end-to-end anastomosis was performed. Histopathological examination of the aneurysm disclosed the presence of fibrosis, scattered chronic inflammatory cells, and a hyalinized fibrin thrombus associated with marked fragmentation and distortion of the elastic tissue. Extensive mucoid deposition in the intima and media of the artery was also detected. The postoperative recovery was uneventful, and the patient was discharged home with regular follow-up during the last year in our outpatient clinic. IMMD can affect smaller vessels such the brachial, coronary, temporal arteries, and dorsalis pedis. The main histological hallmarks of IMMD include intimal and medial thickening caused by the formation of mucin pools, which leads to elastin fibers fragmentation and aggregation. The prognosis of IMMD-related aneurysms is determined by the extent of the disease and the time it is discovered. IMMD-related aneurysms should be included in the differential diagnosis of isolated popliteal artery aneurysms. Open surgical repair is the gold standard of treatment for IMMD-related aneurysms.