In Reply.—We appreciate Dr Bowen's letter calling out attention to the recent reports of prenatal US identification of MCDKs, as well as his thoughts regarding the natural history of these lesions. Although the number of prenatally identified lesions is small, it is interesting to note the high rate of decrease in size documented by the two reports.While decrease in size is understandable, it is hard to explain the complete resorption or dissolution of a dysplastic organ. While many of these kidneys may indeed decrease in size, it is not clear that a decrease in size is equivalent to a decrease in risk to the patient, specifically in regard to the development of hypertension or malignant change.
It is clear that we have inadequate knowledge of the natural history of MCDK to make an unequivocal recommendation for either routine resection or nonoperative observation. Our dilemma revolves around a lack of such information and a documentation of potentially serious complications, such as hypertension and malignant lesions, in retained MCDKs. Since it is unclear whether the risk of these complications is greater in MCDK patients than in the general population, the only definitive statement that can be rendered is that if such lesions are left in place, careful monitoring on a regular basis for the development of such complications is incumbent on the primary physician.