ABSTRACT
Urinary obstruction was defined by Whitaker in 19781 as 'a narrowing of the urinary tract such that the proximal pressure must be raised to transmit the usual flow through it'.
Dilatation of the urinary tract is a well-described consequence of obstruction. However, dilatation may be encountered without any significant increase in intrapelvic pressure; as is the case in patients with megacalicosis. Nonobstructive dilatation can also be found in patients who had their obstruction recently relieved.
