• Imaging
• CT/MRI
• drug abuse
• vascular-Arterial
• wounds
• infection
• mental health

A 40-year-old male intravenous drug misuser presented to the emergency department with a 1-month history of a painful swollen right lower limb. On examination, he was dehydrated, tachycardic and dyspnoeic. Multiple needle marks were identified within the right groin. Extreme right thigh tenderness was elicited on palpation and a fixed flexion deformity of the right hip was present. Laboratory indices revealed a markedly raised white cell count of 78.4×10⁹/l, elevated creatinine of 277 μmol/l and a Staphylococcus aureus bacteraemia. Fluid resuscitation and intravenous antibiotics were commenced. Right thigh colour Doppler ultrasound excluded deep venous thrombosis, but identified a large right groin pseudoaneurysm (figure 1A). Contrast enhanced CT demonstrated a large iliopsoas abscess containing multiple locules of air consistent with gas gangrene and a massive complex pseudoaneurysm arising from the right common femoral artery (figure 1B,C). Endovascular repair or percutaneous thrombin injection were not viable treatment options due to the large pseudoaneurysm size and the co-existing psoas abscess. At surgery, the right external iliac artery was ligated to exclude the pseudoaneurysm and copious foul pus was drained. Four days later, a right hip decortication and lower limb amputation was performed as a result of critical ischaemia. Complete abscess resolution was seen on CT at 20 days (figure 1D).

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Figure 1

Colour Doppler ultrasound of the right groin demonstrates the characteristic “Ying Yang” sign of “to and fro” blood flow within the sac of the pseudoaneurysm. These are identified as red and blue on the colour Doppler image. Note the hypoechoic abscess collection, measuring 3.23 cm deep to the pseudoaneurysm (A). Axial contrast enhanced CT of the lower abdomen demonstrates a large right-sided iliopsoas abscess containing multiple locules of air, consistent with gas gangrene (arrow). Note that the right colon is displaced anteriorly and the right common iliac artery and vein are displaced medially due to the size of the collection (B). Axial contrast enhanced CT of the lower pelvis confirms the ultrasound findings of a massive complex pseudoaneurysm arising from the right common femoral artery (arrow). Note the surrounding iliopsoas abscess extends almost circumferentially around the pseudoaneurysm. There is also some demineralisation of the bone of the anterior right femoral head (C). Non-contrast axial CT abdomen at 20 days post-operation demonstrates minimal residual thickening of the right psoas muscle with no remaining fluid collection (arrow) (D).