To distinguish a solitary (simple, serous) renal cyst from a parenchymal neoplasm is ordinarily easy, requiring a history, physical examination, sedimentation rate determination, and urography. Most solitary cysts give rise to no complaints. They are usually discovered by the patient or physician as rounded, smooth, tense masses in the renal area, or by the radiologist as sharply marginated circular or ovoid shadows adjoining or superimposed upon that of the kidney, in a roentgenogram made for some other purpose. Occasionally, especially in an infant or young child, the cystic nature of a mass may be evident upon transillumination. Renal neoplasms often attract attention because of pain or hematuria, or the presence of a hard or irregular mass. Olovson (9) found the sedimentation rate accelerated in two-thirds of 109 consecutive patients with neoplasms of the renal parenchyma, but observed that it could be normal even in the presence of a large lesion, so that a normal rate is of no significance. Urography is helpful in differentiating the two conditions. The peripheral cyst may cause no deformity of the collecting system; it usually produces only a little broadening of one or two adjoining calyces, which are smooth and sharply marginated. A centrally placed cyst may distort most or all of the calyces or the whole renal pelvis but, if filling is complete, the margins of the collecting system are sharp and clear-cut. Because pressure from the cyst may prevent complete filling in the excretory urogram, a retrograde pyelogram is more likely to be conclusive. A renal neoplasm, on the other hand, usually produces a more ragged or irregular calyceal deformity, with a greater tendency to obliteration of calyces or pelvis. However, as Braasch and Emmett (2), Prather (10), and others have emphasized, an encapsulated neoplasm may feel like, and produce exactly the same deformity as, a cyst of similar size. It is when the findings up to this point are inconclusive, that a supplementary method is needed. The question can be settled by surgical exploration, but it is preferable, if possible, to know the diagnosis beforehand, since; (a) a neoplasm should be removed with its perirenal fascia and fat intact to minimize the danger of local recurrence, which is certainly increased by cutting or tearing into the tumor; (b) nephrectomy should not be done for a resectable cyst; (c) a simple cyst causing no symptoms in a debilitated patient should be left alone. In a symptomless but palpable lesion suggestive of cyst, the diagnosis may often be clinched by diagnostic aspiration and injection of a contrast agent, as recommended by Fish (5) and by Ainsworth and Vest (1). If the resulting shadow in the roentgenogram is sharply marginated, of uniform density, and devoid of filling defects (Fig. 1), the diagnosis of uncomplicated cyst is safe and exploration is unnecessary, particularly in view of the rarity of neoplasms arising within cysts.
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Jul 1, 1967
R M Vertel 
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