Which spleen anomaly is described as the inferior portion located posterolateral to the upper pole of the left kidney and can mimic a mass?

Which spleen anomaly is described as the inferior portion located posterolateral to the upper pole of the left kidney and can mimic a mass?

• A. Accessory spleen
• B. Wandering spleen
• C. Splenosis
• D. Retrorenal spleen

Answer: (D)

The key idea is recognizing that part of splenic tissue can sit behind the kidney and resemble a retroperitoneal mass on imaging. A retrorenal spleen is when a portion of the spleen lies posterior and inferior to the left kidney’s upper pole, in the retroperitoneal space. Because it is still spleen tissue, it has the same echotexture and enhancement patterns as the rest of the spleen, so on ultrasound or CT it can look like a separate mass unless you connect it to the main splenic tissue. Distinguishing this from a true renal lesion comes from looking for splenic origin. On imaging, there should be continuity with the main spleen or a vascular supply consistent with splenic vessels feeding that retroperitoneal piece. The other scenarios don’t fit as neatly: an accessory spleen is another nodular splenic tissue but typically near the splenic hilum; splenosis involves multiple peritoneal implants after splenic injury; a wandering spleen means the entire spleen is abnormally mobile, not just a fragment behind the kidney. The described location and relationship to the left kidney best match a retrorenal spleen.

The key idea is recognizing that part of splenic tissue can sit behind the kidney and resemble a retroperitoneal mass on imaging. A retrorenal spleen is when a portion of the spleen lies posterior and inferior to the left kidney’s upper pole, in the retroperitoneal space. Because it is still spleen tissue, it has the same echotexture and enhancement patterns as the rest of the spleen, so on ultrasound or CT it can look like a separate mass unless you connect it to the main splenic tissue.

Distinguishing this from a true renal lesion comes from looking for splenic origin. On imaging, there should be continuity with the main spleen or a vascular supply consistent with splenic vessels feeding that retroperitoneal piece. The other scenarios don’t fit as neatly: an accessory spleen is another nodular splenic tissue but typically near the splenic hilum; splenosis involves multiple peritoneal implants after splenic injury; a wandering spleen means the entire spleen is abnormally mobile, not just a fragment behind the kidney. The described location and relationship to the left kidney best match a retrorenal spleen.