An Unusual Case of Horseshoe Kidney: Obstructed Drainage or Not?
WH Ma, WY Ho, KK Wong, M Law
Hong Kong J Radiol 2012;15:237-43
Horseshoe kidney is a common congenital anomaly. Complications such as ureteral obstruction, hydronephrosis, recurrent calculi, or infection are common and may require surgical intervention. This report is of a 20-year-old man with known horseshoe kidney. No urinary obstruction in either moiety was detected by technetium-99m–labelled mercaptoacetyltriglycine scintigraphy with diuretic renography performed using posterior acquisition at other hospitals. However, urodynamically significant outflow obstruction in the left moiety was shown on technetium-99m–labelled mercaptoacetyltriglycine study with dual-head acquisition performed subsequently at the Queen Mary Hospital. The diuretic phase of the left moiety based on the anterior views revealed persistent accumulation of radioactive tracer, while the posterior images demonstrated slightly improved drainage in the left moiety after diuretic administration. This patient illustrates an interesting phenomenon of radioactive tracer drainage in a horseshoe kidney. Radioactive tracer usually drains from the posteriorly positioned superior aspect of the kidney to the anteriorly positioned pelvic region. Although the diuretic clearance half-time from the images acquired posteriorly showed improved drainage, there was no improvement in tracer clearance half-time based on the combination of anterior and posterior views. Although diuretic study using posterior acquisition only is useful for differentiating a dilated collecting system from an obstructed urinary system, the result could be misleading for abnormally positioned kidneys. This case illustrates the importance of simultaneous dual-head imaging and the application of the geometric mean in computing diuretic clearance half-time for assessment of renal drainage in an abnormally positioned kidney.
中文摘要
一例罕見馬蹄腎病例：尿路阻塞？
馬慧嫻、何偉然、黃廣權、羅惠明
馬蹄腎的是一種常見的先天性異常，所引發的併發症如輸尿管梗阻、腎積水、復發性結石或尿路感 染並不罕見，且可能需要外科手術。本文報告一名有馬蹄腎的20歲男性，他在其他醫院經99mTc標記 的巰乙酰三甘氨酸（99mTc -MAG3）腎核素動態顯像伴利尿劑腎造影術後視圖，並無發現有尿路梗 阻。但病人其後於瑪麗醫院經雙探頭99mTc -MAG3動態顯像卻發現左腎明顯有尿路流出梗阻。利尿劑腎臟攝影的前視圖顯示左腎放射性示踪劑持續累積，但其給予利尿劑後的後視圖卻顯示左邊的尿液 排出有改善。這病例反映馬蹄腎病人的放射性示踪劑排出的一個有趣現象。一般來說，放射性示踪 劑會由位於後方的腎上端流向位於前方的骨盆區。雖然由後視圖得出的利尿劑清除半衰期提示尿液 引流有改善，但結合前視圖影像後卻發現情況未有改善。縱使利尿劑腎造影術的後視圖可將集合系 統擴張與泌尿系統梗阻區分開來，但對於腎位置異常的病人來說，後視圖可能會誤導病情。本病例 顯示同時使用雙探頭影像及利尿劑清除半衰期的幾何平均數，對於評估腎位置異常的病人的腎臟引 流情況相當重要。