Idiopathic Retroperitoneal Hematoma Associated With Anticoagulation in a Patient With Moderate COVID-19 Pneumonia: A Case Report.

We report a case of idiopathic retroperitoneal hematoma in an 82-year-old man with moderate COVID-19 pneumonia receiving prophylactic anticoagulation therapy. The patient was initially treated with remdesivir, dexamethasone, and subcutaneous heparin, showing improved respiratory function. On hospital day 6, he developed sudden right lower abdominal pain without prior trauma. Physical examination revealed abdominal distension and tenderness. Laboratory tests showed no evidence of coagulopathy. Contrast-enhanced computed tomography identified active bleeding in the right iliopsoas muscle, consistent with retroperitoneal hematoma. The patient was transferred to a tertiary center for management. This case underscores that retroperitoneal hematoma can occur even in moderately ill COVID-19 patients without abnormal coagulation markers. Vigilant physical examination and early imaging are essential for timely diagnosis. Individualized risk assessment is critical when initiating anticoagulation therapy in elderly patients with comorbidities.