A 54-year-old woman is brought to the hospital due to fever, nausea, vomiting, and confusion. For the past 3 days, she has had dysuria and increased frequency of urination. Medical history is significant for recurrent urinary tract infections and primary hypertension. Family history is insignificant. Temperature is 39.2 C (102.6 F), blood pressure is 90/50 mm Hg, pulse is 102/min, and respirations are 24/min. Examination shows right flank tenderness. The patient subsequently undergoes nephrectomy, and a cut section of the resected kidney is shown in the image below. Further evaluation of this patient would most likely reveal which of the following?

Question

A 54-year-old woman is brought to the hospital due to fever, nausea, vomiting, and confusion.  For the past 3 days, she has had dysuria and increased frequency of urination.  Medical history is significant for recurrent urinary tract infections and primary hypertension.  Family history is insignificant.  Temperature is 39.2 C (102.6 F), blood pressure is 90/50 mm Hg, pulse is 102/min, and respirations are 24/min.  Examination shows right flank tenderness.  The patient subsequently undergoes nephrectomy, and a cut section of the resected kidney is shown in the image below.  Further evaluation of this patient would most likely reveal which of the following?

Quizplus · Accepted Answer

11ec160b_3a49_5bd8_9249_99126a49c7f9_MD0001_00 This patient has a large staghorn calculus in the renal pelvis associated with dilation of the collecting system and atrophy of the renal cortex. Staghorn calculi are composed primarily of struvite (magnesium ammonium phosphate) and calcium salts (carbonate, oxalate, or phosphate). They are typically seen in patients with recurrent upper urinary infection caused by urease-producing organisms (eg, Proteus, Klebsiella); hydrolysis of urea yields ammonia, which alkalinizes the urine (pH usually >7) and facilitates precipitation of magnesium ammonium phosphate crystals (Choice E). Because of the large quantities of urea excreted in urine, these stones can grow very rapidly and fill the renal calyces, causing obstruction of renal outflow. The kidneys are often atrophic due to recurrent infection and/or chronic obstructive nephropathy. The large size of staghorn calculi prevents them from passing into the ureter, so symptoms are typically related to the associated infection (eg, fever, mild costovertebral pain, hematuria) rather than acute renal colic. (Choice A) Escherichia coli is the most common cause of uncomplicated urinary tract infections but only rarely produces urease. It is not commonly associated with the formation of staghorn calculi. (Choice B) Cystine stones are uncommon, yellow-brown calculi that precipitate in acidic urine. They usually develop in patients who have cystinuria secondary to genetic defects impairing renal cystine reabsorption. Although cystinuria can sometimes result in large staghorn calculi due to persistent cystine excretion, this patient's recurrent urinary tract infections are more suggestive of struvite stone formation. (Choice D) Hyperparathyroidism due to a parathyroid adenoma can cause increased serum calcium levels that ultimately result in increased urinary calcium filtration, predisposing to formation of calcium oxalate stones. These stones typically present with renal colic due to acute ureterolithiasis, and most patients do not have significant fever or a history of recurrent urinary tract infection. Educational objective: Staghorn calculi are large renal stones that take on the shape of the renal calyces. They are composed primarily of struvite (magnesium ammonium phosphate) and are associated with recurrent upper urinary tract infections by urease-producing organisms (eg, Proteus, Klebsiella). Hydrolysis of urea yields ammonia, which alkalinizes the urine and facilitates precipitation of struvite crystals.

A 54-Year-Old Woman Is Brought to the Hospital Due to Fever