A 26-year-old man comes to the emergency department due to sudden onset of severe, colicky, left-sided flank pain that radiates to the scrotum. He also has nausea, vomiting, and dark urine. The patient has never before had these symptoms. Examination shows no abnormalities. Noncontrast helical CT scan reveals a 5-mm radiopaque stone in the left upper ureter. Laboratory results are as follows: Urinalysis shows hematuria but no casts. Which of the following is the most likely cause of this patient's symptoms?

Question

A 26-year-old man comes to the emergency department due to sudden onset of severe, colicky, left-sided flank pain that radiates to the scrotum.  He also has nausea, vomiting, and dark urine.  The patient has never before had these symptoms.  Examination shows no abnormalities.  Noncontrast helical CT scan reveals a 5-mm radiopaque stone in the left upper ureter.  Laboratory results are as follows:  Urinalysis shows hematuria but no casts.  Which of the following is the most likely cause of this patient's symptoms?

Quizplus · Accepted Answer

11ec25c8_d4f4_ea55_bc81_5fafd5cf5766_MD0003_00 This patient has acute ureterolithiasis, with severe flank pain, vomiting, and hematuria. Acute obstruction of the ureter at the vesicoureteral junction produces pain that radiates to the groin or inner thigh. Calcium oxalate stones are the most common type of kidney stone, accounting for >75% of stones in adults; patients may also have stones composed of a mixture of calcium oxalate and calcium phosphate. Because of their high calcium content, the stones are radiopaque and easily visible on x-ray and CT scan. In addition to hematuria, which is common with any stone, urine microscopy can often identify envelope-shaped calcium oxalate crystals; however, their presence is neither sensitive nor specific for oxalate stones. Although an increased filtered calcium load can increase the risk of stones, serum calcium levels are normal in most patients. vesicoureteral junction Risk factors for calcium oxalate stones include dehydration, excess sodium or oxalate in the diet, obesity, and hyperparathyroidism. In addition, in malabsorptive syndromes (eg, Crohn disease, bowel resection) calcium can form soap complexes with fat in the intestinal lumen and therefore remain unavailable to form nonabsorbable complexes with oxalate; as a result, free oxalate absorption is increased, and oxalate is subsequently filtered into the urine, promoting the formation of oxalate stones. (Choice B) Some patients may have stones composed of a mixture of calcium oxalate and calcium phosphate, but pure calcium phosphate stones are less common than oxalate stones. (Choice C) Cystine stones are uncommon and usually develop in patients with cystinuria secondary to genetic defects in renal reabsorption. Most patients have a positive family history. (Choice D) Struvite stones are usually caused by urease-producing bacteria (eg, Proteus). Struvite forms large, chronic stones that can fill the renal pelvis; most patients have a history of recurrent upper urinary tract infections. (Choice E) Uric acid stones are formed when uric acid excretion is increased (eg, gout, myeloproliferative disorders) or the urine is acidic (eg, obesity, chronic diarrhea). Uric acid stones are radiolucent (though may be visible on CT scan) and are significantly less common than oxalate stones. Educational objective: Calcium oxalate stones are the most common type of kidney stone; patients may also have stones composed of a mixture of calcium oxalate and calcium phosphate. Risk factors include dehydration, excess sodium or oxalate in the diet, obesity, hyperparathyroidism, and malabsorptive disorders. Calcium-containing stones are radiopaque. References: Kidney stone disease: an update on current concepts. (http://www.ncbi.nlm.nih.gov/pubmed/29515627)

A 26-Year-Old Man Comes to the Emergency Department Due to Sudden