We present a case of a large spontaneous retroperitoneal hematoma originating from the left iliopsoas muscle with a concomitant history of pneumocystis jirovecii pneumonia, immunosuppression, and renal transplant. 

Pneumocystis jirovecii pneumonia classically appears as a honeycombing of the lung parenchyma with ground glass opacities, septal thickening, and pneumatoceles. These are clearly evident in the CT Thoraces of this patient. This infection is very common in renal transplant patients. Patients tend to succumb to respiratory failure due to decreased gas exchange within the lungs leading to fatal respiratory distress. The condition is treated with TMP-SMX and steroids primarily. 

Spontaneous iliopsoas muscle hematoma generally occurs in patients taking anticoagulant medication. This patient, interestingly enough, was not taking any medication of the sort. Hematomas appear as high-density fluid with fluid-fluid levels on CT. The contrast in the arterial phase can clearly be seen extravasating into the blood collection within the retroperitoneum. Depending on the size of these hematomas, exploratory surgery or embolization may be required to provide hemostasis to prevent hemorrhagic shock. This patient was severely immunosuppressed and already unstable due to the concomitant PJP. It was hypothesized that the cause for this bleed was due to clotting dysfunction secondary to severe systemic immunosuppression and PJP.