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In space-occupying lesions of the kidney or the urinary system in general, ultrasonography is used as the initial imaging method (Figs. 3.80, 3.81C), since conventional radiography is often unsuccessful in determining the extent and cause of the disease. Ultrasound and CT usually allow differentiation of cysts from tumors and their extension within the kidney (von Sinner et al, 1993). However, in some complex or atypical cystic masses, differentiation may be impossible. Precise assessment of relationships to neighboring organs and vascular structures generally is possible. In hydatid disease, characteristic structures such as daughter cysts or collapsed parasitic membranes may be seen. Ultrasonography and nonenhanced CT also may detect minor calcifications in the lesion (Figs. 3.81 and 3.82).

The CT and sonographic appearances of renal hydatidosis have been amply described, with both studies yielding important and often quite similar information. The findings are not, however, pathognomonic in most cases. In its earliest stages of development, a round anechoic cyst is identifiable on sonography, whose wall may be somewhat thicker than that seen with simple serous cysts (Fig. 3.80). Calcification is frequent, and "sand" may be encountered. Hydatid cysts tend to have a low CT attenuation value when unilocular but, as daughter cysts are formed, the CT appearance becomes heterogeneous (Fig. 3.82). The daughter cysts, however, which usually arrange themselves peripherally within the mother cyst, almost invariably exhibit a lower CT attenuation value than does the parent cyst, resulting in somewhat of a rosette appearance. When daughter cysts are produced, CT or sonography will reveal a multilocular structure with curvilinear "septa", which are actually the opposing walls of the daughter cysts (Fig. 3.82).

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Fig. 3.80 (A-D) Ultrasound scans showing a 6.6 cm circumscribed, heterogeneous mass in the left kidney with through transmission in a 15-year-old boy from Zimbabwe. (E) Plain radiograph of the left abdomen showing the large flank mass. (Courtesy of Dr. Sam Mindell, Harare, Zimbabwe).

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Fig. 3.81 Right renal hydatid in a 45-year-old Saudi Arabian woman who complained of right flank pain of 20 years duration. (A) Precontrast CT of the abdomen demonstrates a large 8 x 6.5 cm mass in the lower pole of the right kidney. The lesion is not typically cystic (density is 40 Hounsfield units). Scattered calcifications are noted in the anterior part of the lesion. (B) After an intravenous bolus of contrast medium, the lesion's density remains unchanged, while the left kidney shows normal contrast enhancement. (C) Ultrasonography (sagittal view) of the right kidney reveals a low echogenic lesion (arrows) in the lower pole. (D) Selective right renal arteriography reveals large avascular mass in the lower pole. Densities in the lower part of the lesion represent calcifications. Echinococcus titer and chest x-ray were normal, but a hydatid cyst was still suspected. Surgery was performed to rule out tumor. Preoperatively, the patient received 200 mg. albendazole orally every 6 hours for 2 days and 3 gm. praziquantel the day before surgery. She was also premedicated with 100 mg. hydrocortisone and 25 mg. diphenhydramine hydrochloride to reduce the risk of an allergic reaction. The lower pole of the right kidney with the mass was then removed without leakage of cyst contents. Histopathology revealed a 9 cm cystic mass with a fibrous wall, which contained necrotic whitish-gray cheesy material with focal areas of hemorrhage, cholesterol clefts and calcification, as well as many hooklets, confirming hydatid disease. Postoperatively, she received 200 mg. albendazole twice daily for 1 month and had an uneventful convalescence. (Courtesy of Dr. von Sinner and J Urology, 1993).

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Fig. 3.82 CT appearance of hydatid cyst of the kidney in a 64-year-old man from Uruguay with palpable right flank mass. (A) Contrast-enhanced CT reveals a large right renal mass. The wall is densely calcified and discrete low-attenuation cysts are noted within a somewhat higher attenuation matrix. (B) A more caudal CT section reveals multiple daughter cysts arranged in rosette formation about the periphery of the mother cyst. Fine, delicate internal calcifications can be seen. Surgery revealed large hydatid cysts. No other intra-abdominal manifestations of hydatid disease were encountered. (courtesy of Drs. Jose and Felix Lerborgne, Montivideo, Uruguay, and H. Pollack: Clinical Urography, 2nd ed. Philadelphia, Saunders, 1999).

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