Case Report: Iliac perivascular myeloid sarcoma presenting with iliofemoral deep vein thrombosis and hydronephrosis.

Myeloid sarcoma (MS) is a rare extramedullary tumor of myeloid blasts that may occur before, concurrently with, or after acute myeloid leukemia (AML) (1-4). We report a 53-year-old man with progressive left lower-limb pain and swelling, initially admitted to the vascular surgery service, with imaging revealing left external iliac vein and proximal common femoral vein occlusive thrombosis, a peri-iliac mass encasing the iliac vessels, and ipsilateral hydronephrosis. Biopsy of the left inguinal lesion showed MPO positivity, CD34 positivity, partial TdT positivity, and a Ki-67 index of about 80%, supporting myeloid sarcoma. Bone marrow studies confirmed AML with maturation, with 55% blasts, a myeloid immunophenotype, CEBPA (TAD1) positivity, and a complex karyotype. Baseline fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) demonstrated irregular perivascular soft tissue extending from the left common to external iliac vessels, with mild FDG uptake. The patient received AML-directed therapy, including two IA cycles and high-dose cytarabine, achieving morphologic complete remission with a marked PET/CT response. During follow-up, measurable residual disease (MRD) fluctuated repeatedly despite continued morphologic remission, prompting venetoclax-based therapy, including cytarabine plus venetoclax, azacitidine plus venetoclax with homoharringtonine, and later azacitidine plus venetoclax combined with tislelizumab. At the last follow-up in December 2025, the patient remained alive. This case highlights that peri-iliac MS may mimic vascular and urologic disease and that serial MRD monitoring can be useful for guiding postremission treatment adaptation in AML with extramedullary disease.