Non-traumatic Iliacus Muscle Hematoma During Anticoagulation Bridging in a Patient With Active Malignancy: A Case of Multifactorial Bleeding Risk.

Patients with malignancy are at increased risk of bleeding due to tumor-related vascular fragility, chemotherapy-induced thrombocytopenia, impaired hepatic function, malnutrition, and systemic inflammation. Anticoagulation management in this population is further complicated by frequent medication changes, drug-drug interactions, poor oral intake, and acute illness, making bridging anticoagulation a particularly high-risk transition. We report a case of a non-traumatic iliacus muscle hematoma occurring during therapeutic-dose enoxaparin bridging in a patient with active metastatic malignancy, illustrating how multiple concurrent risk factors can precipitate clinically significant hemorrhage even when the international normalized ratio (INR) appears subtherapeutic or within range. A 67-year-old man with metastatic squamous cell carcinoma of the lung and larynx, atrial flutter on chronic warfarin therapy, and concurrent thrombocytopenia developed progressive anemia during hospitalization. Warfarin was held for a planned procedure, and bridging anticoagulation with therapeutic-dose enoxaparin was initiated. Imaging subsequently identified a 3.5 × 2.4 × 5.5 cm left iliacus muscle hematoma without evidence of trauma or active extravasation. The patient was managed conservatively with serial monitoring and individualized anticoagulation adjustments, resulting in hemoglobin stabilization and clinical improvement. This case reinforces the multifactorial nature of bleeding risk in patients with malignancy receiving anticoagulation and highlights that INR alone does not fully capture hemorrhagic risk when additional anticoagulants, thrombocytopenia, renal impairment, and cancer-related hemostatic alterations are present.