E1754. How to Face Findings of Bilateral Renal and Perinephric Involvement
  1. Joana Granadas; Hospital Professor Doutor Fernando Fonseca
  2. Gisela Andrade; Hospital Professor Doutor Fernando Fonseca
  3. Sérgio Ferreira; Hospital Professor Doutor Fernando Fonseca
A wide spectrum of entities can affect both kidneys simultaneously and eventually both perinephric spaces. It ranges from inflammatory or vascular conditions to neoplasms. They may be common or uncommon, benign or malignant, some are hereditary while others are acquired.

Educational Goals / Teaching Points
Review the spectrum of entities that can present with bilateral renal/perinephric involvement. Illustrate the imaging patterns of those conditions. Provide clinical and radiological clues that should help narrow the differential diagnosis.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Inflammatory conditions cover multiple pathological processes. Included in this category are infectious diseases, which have many possible imaging patterns, namely: enlargement of the kidneys; focal hypoattenuating lesions (wedge-shaped/round), occasionally with mass effect; gas in renal parenchyma/collecting system. These findings can be bilateral. They should be promptly distinguished from infarcts and neoplasms, which may have similar presentations. Features such as thickening of the renal fascia and the septa in the perinephric space, in association with clinical and laboratory findings of infection, suggest the diagnosis. Multiple vascular disorders can affect the kidney. Renal infarcts usually present as focal lesions and can be bilateral. The wedge-shaped morphology of these hypoattenuating lesions, the existence of infarcted areas in other organs and of thrombi in the aorta, renal artery or vein suggest this etiology. The main differential diagnosis is infection. Distinguishing neoplastic from non-neoplastic conditions can be difficult, but even the conviction of dealing with a neoplasm carries diagnostic challenges. The first challenge is to differentiate a benign from a malignant neoplasm. Malignancies and benign tumors may have overlapping characteristics and can show bilateral involvement. For instance, there are poor lipid angiomyolipomas and rarely renal cell carcinomas may have macroscopic fat components. The second challenge is to distinguish metastasis from primary renal malignancies. A person who develops a malignancy is at greater risk of developing others. Despite multiple bilateral lesions more likely correspond to metastasis, sometimes primary malignant renal tumors may also be multiple and bilateral. Histological characterization is often needed to confirm the diagnosis, but looking for other clinical and radiological manifestations may aid in the identification of the most probable hypothesis (e.g. knowing a patient is affected by tuberous sclerosis may suggest the hypothesis of angiomyolipomas; the presence of metastasis in other organs may point to the hypothesis of metastatic disease).

Imaging plays a key role in the recognition of conditions with bilateral renal/perinephric involvement. However, findings are frequently nonspecific and often there are overlapping features that complicate the differential diagnosis. Accurate identification of the most likely etiology is crucial as it will determine the management. As always, clinical context is invaluable to guide the Radiologist.