Imaging description

CT imaging characteristics of hydronephrosis due to renal calculus disease partially overlap with alternate etiologies which may be mistaken for hydronephrosis.

Evaluation of CT images usually starts with side-to-side comparison of both kidneys to evaluate for secondary signs of urinary tract obstruction (Figure 68.1A, 68.2A). Thereby the clinical history is tremendously helpful to correctly identify the affected side.

In pseudohydronephrosis, a portion of the urinary tract is enlarged, or appears dilated, by fluid density material (Figure 68.1). However, on CT asymmetric stranding in the perinephric fat, unilateral ureteric dilation and unilateral renal enlargement of the affected side are usually absent [1].

Renal and ureter stones of clinical relevance are virtually all visible on non-contrast CT [2, 3]. Pseudohydronephrosis will not be associated with an obstructing calculus in the urinary tract.

At times, a very full urinary bladder can prevent unobstructed flow of urine and lead to dilation of the renal collecting system, mimicking hydronephrosis (Figure 68.3).

Importance

Pseudohydronephrosis can be mistaken for urinary tract obstruction from renal stone disease. Renal and ureter stones of clinical relevance are virtually all visible on non-contrast CT [3]. Even on contrast-enhanced CT, urinary tract obstruction can usually be differentiated from pseudohydronephrosis (Figure 68.4).