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Case 1: A 23-year-old female third-year medical student who has no medical history seeks treatment for abdominal distention. She takes an estrogen-containing birth control pill and does not smoke or consume alcohol. Family history is unremarkable. Physical examination is significant for abdominal distention, and an abdominal fluid wave is detected. Complete blood count is normal. Imaging confirms occlusive thrombosis of the main portal vein. On endoscopy, grade 1 to 2 esophageal varices are noted and banded. Unfractionated heparin is begun. Subsequent workup reveals a homozygous factor V Leiden mutation. Long-term anticoagulation is planned, and she asks if warfarin can be avoided given her hectic ward rotations, erratic diet, and need for monitoring. Case 2: A 35-year-old woman who has no medical history seeks treatment for progressively worsening posterior headaches for 1 week. Magnetic resonance imaging of the brain shows dural sinus thrombosis with associated small areas of petechial cerebral hemorrhage. She is started on a continuous unfractionated heparin infusion and admitted to the hospital for further observation. Her grandmother is on warfarin for atrial fibrillation, and the patient would prefer to avoid warfarin because she does not think she can comply with the frequent monitoring that will be required. She inquires about other oral anticoagulant options for her condition.

Although much less common than deep vein thrombosis of the lower extremities or lungs, clots in unusual locations, including the splanchnic, cerebral, retinal, upper-extremity, and renal locations, present with significant morbidity and mortality. In the last 2 decades, treatment of clots in these unusual locations is primarily managed medically, with interventional and surgical approaches reserved for more severe or refractory cases. The hematologist is well positioned to provide consultation to organ-specific specialties (ie, neurosurgery, hepatology, ophthalmology), especially because acquired and congenital hypercoagulability plays a major role, and anticoagulation is often the primary treatment. Historically, treatment has been based on expert opinion, but systematic reviews and meta-analyses have recently been published. Various societies have produced guidelines for the treatment of clots in unusual locations; however, randomized clinical trial data remain scarce. In the last few years, increasing data have emerged concerning the efficacy of the direct oral anticoagulants in treating clots in unusual locations. Cases have recently been described highlighting atypical thrombosis associated with COVID-19 infection as well as with the ChAdOx1 nCoV-19 (AstraZeneca) vaccine and Johnson and Johnson's Janssen Ad26.COV2.S vaccine. This article reviews clots in unusual locations with an emphasis on the splanchnic (mesenteric, portal, splenic, hepatic) and cerebral circulation. Through a case-based approach, key questions are posed, and data are presented to help guide diagnosis and treatment.

Thromboembolism related to a mechanical heart valve (MHV) is a major complication after surgical valve replacement. Warfarin remains as guideline-endorsed thromboprophylaxis in patients with MHVs. Alternative anticoagulation therapy for patients who do not tolerate or who fail warfarin is not adequately covered in the current guidelines. We report a case of successful long-term anticoagulation with enoxaparin in a patient with a mechanical aortic valve who had a contraindication to warfarin. The patient developed a left thigh hematoma requiring surgical evacuation 1 month after initiation of weight-based dosing of enoxaparin. His dose was then titrated based on peak anti-factor Xa levels (goal 0.6-1.0 IU/ml). He remained free of signs and symptoms of thromboembolic events, valve dysfunction, bleeding complications, or major adverse effects from long-term enoxaparin use for the next 13 years. Our case provides promising evidence of the potential role of enoxaparin in patients with MHVs in whom warfarin thromboprophylaxis is not possible. Meticulous monitoring of anti-factor Xa levels and dosage adjustments are crucial to treatment success.