Pyrexia of unknown origin: inferior vena cava agenesis.

A 26-year-old woman presented with a 5-day history of fever after returning from Bali. She denied sexual contact abroad. On examination, there was suprapubic tenderness and a widespread maculopapular rash. Malaria serology was negative and blood tests were normal except for an elevated C reactive protein. Treatment was initially with ceftriaxone, metronidazole and doxycycline, but her symptoms failed to improve. A CT pelvis suggested a possible tubo-ovarian abscess, a suspected inferior vena cava (IVC) anomaly and left internal iliac/femoral venous thrombosis. A gynaecology review demonstrated left tubo-ovarian tenderness and fullness. An MRI suggested pelvic inflammatory disease and thrombophlebitis affecting the pelvic veins; deep vein thrombosis (DVT) treatment was commenced. Further family history revealed thrombosis throughout multiple generations. Further imaging analysis demonstrated agenesis of the IVC with compensatory dilation of pelvic collaterals and an acute DVT of the deep pelvic venous system. The patient was discharged with direct oral anticoagulant therapy.