Alex Liang, Rachna Subramony
A 48 year old male with past medical history of Crohn’s Disease, cryptogenic cirrhosis, pancytopenia, portal vein thrombosis, Factor V Leiden, and prior history of kidney stones presenting with right sided flank pain, dysuria, and hematuria worsening over the past 4 days. He reports similar symptoms in the past associated with his previous findings of kidney stones. He denies fever, nausea, vomit, diarrhea, chest pain, shortness of breath, or anuria.
Vitals: BP 123/80 mmHg | Pulse: 101 | Temp: 98.5 °F (36.9 °C) | Resp: 20 | Wt: 65.8 kg (145 lb) | SpO2: 97%
On physical examination, the patient is alert and uncomfortable but not in acute distress. Abdominal examination reveals a soft, non-distended abdomen with right flank and right costovertebral angle (CVA) tenderness. The remainder of the physical exam, including cardiac, pulmonary, and neurologic exams, was unremarkable.
A bedside ultrasound was performed on the right kidney.
Figure 1: Several renal calculi in the medullary pyramids of the right kidney. The largest measures approximately 6.8mm in diameter.
Discussion
Nephrolithiasis, commonly referred to as kidney stones, is a prevalent condition with an estimated annual incidence rate of approximately 0.5% to 1% in the general population and a lifetime risk of 10%-15% with higher prevalence among men. Risk factors for nephrolithiasis include dehydration, dietary factors (high sodium or oxalate intake), obesity, metabolic syndrome, and recurrent urinary tract infections1,2.
The differential diagnosis for nephrolithiasis includes conditions that present with acute flank pain, hematuria, and urinary symptoms. Such conditions include pyelonephritis, renal infarction, or ureteropelvic junction obstruction. In this patient, the presentation of acute right flank pain with costovertebral angle tenderness accompanied by dysuria and gross hematuria is strongly indicative of nephrolithiasis.
On physical examination, patients with nephrolithiasis typically present with costovertebral angle tenderness on the affected side with otherwise minimal abdominal findings. The clinician should be attentive of systemic signs such as fever and tachycardia, as they may suggest a concurrent urinary tract infection or obstructive pyelonephritis and require further work up. In this case, the patient presented without fever or systemic signs of infection, supporting a diagnosis of uncomplicated nephrolithiasis.
While non-contrast computed tomography (CT) of the abdomen and pelvis is the gold standard for diagnosing nephrolithiasis, ultrasound remains an asset in the detection of stones with a sensitivity of 54% and specificity of 71%. In some cases, such as in pregnant patients, ultrasound is the preferred modality due to its lack of ionizing radiation. In this case, a renal ultrasound revealed several stones in the medullary pyramids of the right kidney, with the largest measuring 6.8mm in diameter. It is important to note that CT does have higher sensitivity (88%) and lower specificity (58%) compared to ultrasound. Despite this, no evidence has shown that increased CT use is associated with improved patient outcomes when compared to ultrasonography 3.
When performing a point-of-care ultrasound (POCUS) exam for nephrolithiasis, the curvilinear or phased-array transducer should be placed in the flank region along the midaxillary line to obtain longitudinal and transverse views of the kidney. The exam focuses on the identification of hydronephrosis, which appears as anechoic dilation of the renal collecting system, and the detection of renal calculi, which appear as echogenic foci with posterior acoustic shadowing.
Management of nephrolithiasis depends on the size and location. Stones that are less than or equal to 5mm are typically managed conservatively with hydration and analgesia. Medication such as tamsulosin can be given to aid in the expulsion of the stones. Stones that are 10mm or greater, causing significant obstruction, or with concurrent infection or renal impairment often require more invasive measures such as extracorporeal shock wave lithotripsy (ESWL), ureteroscopy with laser lithotripsy, or percutaneous nephrolithotomy 4.
Recurrence of nephrolithiasis is common, with a rate of approximately 50% within 10 years. Patients can decrease this risk with preventative strategies such as dietary modifications (increased fluid uptake, reduced sodium and oxalate consumption) and addressing underlying metabolic abnormalities 4.
References
- Pearle MS, Calhoun EA, Curhan GC. Urologic Diseases in America Project: Urolithiasis. J Urol. 2005;173(3):848–857. doi:10.1097/01.ju.0000152082.14384.d7.
- Scales CD, Smith AC, Hanley JM, Saigal CS. Prevalence of Kidney Stones in the United States. Eur Urol. 2012;62(1):160–165. doi:10.1016/j.eururo.2012.03.052.
- Smith-Bindman R, Aubin C, Bailitz J, et al. Ultrasonography versus Computed Tomography for Suspected Nephrolithiasis. N Engl J Med. 2014;371(12):1100-1110. doi:10.1056/NEJMoa1404446.
- Curhan GC. Epidemiology of Stone Disease. Urol Clin North Am. 2007;34(3):287–293. doi:10.1016/j.ucl.2007.05.003.