Differential Diagnosis

• Single most likely diagnosis
  • Acute pyelonephritis with possible renal vein thrombosis: The description of a diffusely enlarged left kidney with a heterogeneous T2 signal and a striated appearance at the nephrographic phase, along with multiple cortical non-enhancing areas and no excretion of contrast in the delayed phase, strongly suggests an infectious and inflammatory process such as acute pyelonephritis. The low signal filling defect at the left renal vein close to the renal hilum could represent thrombosis, which is a known complication of pyelonephritis, especially in patients with predisposing factors like nephrotic syndrome or dehydration.
• Other Likely diagnoses
  • Renal infarction: The presence of multiple cortical non-enhancing areas could also suggest renal infarction, which might be due to embolic events or thrombosis. However, the clinical context and the rest of the imaging findings would help differentiate this from pyelonephritis.
  • Severe hydronephrosis with infection: Although there's no mention of PCS (pelvic-calyceal system) obstruction, severe hydronephrosis could potentially cause a similar appearance, especially if complicated by infection. However, the absence of significant perinephric fluid collection and the specific mention of no PCS obstruction makes this less likely.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Renal cell carcinoma with venous thrombosis: Although less likely given the acute presentation and the specific imaging characteristics, renal cell carcinoma with tumor thrombus extending into the renal vein is a critical diagnosis not to miss. It would typically present with a more solid mass and might not have the same level of heterogeneous signal and cortical non-enhancing areas as described.
  • Sepsis or systemic infection leading to renal dysfunction: The clinical context is crucial; if the patient is septic or has a systemic infection, the renal findings could be part of a multi-organ dysfunction syndrome. Early recognition and treatment of the underlying cause are critical.
• Rare diagnoses
  • Xanthogranulomatous pyelonephritis (XGP): A rare form of chronic pyelonephritis that could present with a similar appearance of a non-functioning kidney and might have areas of low attenuation due to the presence of foam cells and calculi. However, XGP typically has a more chronic presentation and might show additional features like calculi or a mass-like appearance.
  • Renal lymphoma: Although rare, renal lymphoma could present with multiple lesions and a non-functioning kidney. It would be an unusual presentation for lymphoma but could be considered in the differential diagnosis, especially if there are systemic symptoms or other signs of lymphoma.