INTRODUCTION	Section 2 of 11
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Background: In the past, multilocular cystic renal tumors have been considered to be lesions of developmental origin, hamartomas, or hamartomas with malignant potential. In 1956, Boggs and Kimmelstiel first proposed the true neoplastic nature of the lesions in a case report, suggesting the term benign multilocular cystic nephroma for this condition.

More recently, Joshi and Beckwith proposed a modification to the existing terminology. Their modification emphasized a neoplastic rather than a developmental or hamartomatous origin. First, they recommended that the term cystic nephroma be used to describe a multicystic tumor lacking blastemal or other embryonal elements. Second, they suggested that the term cystic partially differentiated nephroblastoma (CPDN) be used to denote a predominantly cystic lesion without nodular solid regions and in which the septa contain blastemal or other embryonal elements. Furthermore, they proposed that both terms be used as subsets of the category term multilocular cystic renal tumor.

Pathophysiology: Multilocular cystic renal tumor is characterized as a solitary, well-circumscribed, multiseptated mass of noncommunicating fluid-filled loculi that is surrounded by a thick fibrous capsule and compressed renal parenchyma. The mass is typically large. Madewell et al discovered that the mean size of the mass is 7.6 X 9.7 cm. Kettritz et al reported solitary tumors sized 3.3-13 cm, with an average maximum diameter of 6.7 cm.

The most commonly reported location for this tumor originates at the lower pole, although tumors have been known to originate in other areas. Kettritz et al discovered tumors that originated in the middle third of the kidney in 5 patients, in the upper pole of the kidney in 1 patient, and in the lower pole of the kidney in 1 patient. All 7 lesions were multiseptated cysts, arising in the right kidney in 3 patients and in the left kidney in 4 patients.

The contents of the cyst consist of either clear-to-yellow fluid (similar to serum) or thick myxomatous gel. Although complications are unusual, cyst herniation into the renal pelvis has been described as occurring most frequently. On gross inspection, solid nodules of tissue are not discernible, and hemorrhage and necrosis is usually not found. Calcification is also uncommon.

Frequency:

• In the US: Multilocular cystic renal tumors are rare; therefore, determining the true prevalence and the age and sex distributions is difficult.

Mortality/Morbidity: No mortality is associated with this disease. Morbidity is related to the single functional kidney.

Race: Multilocular cystic nephroma has no racial predilection.

Sex: Multilocular cystic renal tumors have been noted to affect males, predominantly in childhood, and females, predominantly in adulthood.

Age: Castillo et al found that two thirds of the tumors occurred in children aged 3 months to 2 years, with a male-to-female predominance ratio of 2:1. Of tumors in this group, almost 50% contained blastema; therefore, they were classified as CPDNs.

Of patients aged 30 years or older (approximately 30% of patients), an 8:1 female-to-male predominance was found. Of this group, fewer than 20% of tumors were CPDNs. Other groups have reported similar results. Madewell et al found that, in childhood, 73% of cases occurred in boys younger than 4 years. In patients older than 4 years, 89% of cases occurred in females, who presented with findings of an abdominal mass.

Anatomy: Anatomically, cystic nephroma and CPDN are identical; however, they are histologically distinct. In cystic nephroma, as defined by Joshi and Beckwith, the septa consist of fibrous tissue that may contain well-differentiated renal tubules but no poorly differentiated tissues or blastemal cells. CPDN has the histologic features of cystic nephroma with the addition of septal blastemal cells in any amount, with or without other embryonal stroma or epithelial cell types.

CPDN can be further classified as grade 1 or 2 tumors. In grade 1 CPDN, the relatively mature subtype, the septa contain more than 50% mature elements. Grade 2 CPDNs contain less than 50% mature septal elements.

A CPDN must also be pathologically distinguished from a Wilms tumor (its primary differential diagnosis), in which cysts have formed as a consequence of hemorrhage and necrosis in solid tissue.

Clinical Details: Multilocular cystic renal tumors are usually detected in children when a caretaker or physician incidentally discovers a painless abdominal mass. In adults, signs and symptoms are nonspecific; the most common include pain, hematuria, and urinary tract infections. No serologic marker for the lesions has been found.

In CPDN, when blastema is present in the septa of a multilocular cystic renal tumor, the potential for more aggressive behavior is implied despite the usually benign course of the tumor. In patients with these findings, surgery is required for diagnosis, because neither clinical examination nor radiologic evaluation is useful in predicting the histologic characteristics. If the tumor proves to be CPDN, regular noninvasive monitoring is advocated.

The demonstration of septa is necessary to distinguish multilocular cystic renal tumors from simple cysts. The demonstration of thin septa and the lack of enhancing nodules within the tumor must be seen to help establish the preoperative diagnosis of the tumor, which may be important to direct more conservative surgical therapy.

Preferred Examination: Ultrasonography (US) is the first radiologic examination performed for the evaluation of any abdominal mass. US can provide the imaging results necessary for diagnosing multilocular cystic nephroma. The diagnosis may be confirmed by using either CT or MRI. Together, US and CT may be the studies of choice because they enable the evaluation of cystic lesions, stromal tissue, and the perfusion of this stroma. No flow is seen within the cystic lesions.

Limitations of Techniques: The precision and accuracy of US depends on, and therefore is limited by, the operator's skill.

CT may not be chosen if the patient has a severe allergy to the contrast medium.