Nephrolithiasis

Published on 14/03/2015 by admin

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112 Nephrolithiasis

Carl R. Menckhoff

Key Points

• Ureteral calculi smaller than 5 mm in diameter spontaneously pass through the urinary tract in 90% of cases, whereas stones larger than 8 mm in diameter cause impaction in 95% of instances.

• Impaction most commonly occurs at the ureterovesical junction, the ureteropelvic junction, or the pelvic brim.

• Abdominal aortic aneurysms are commonly misdiagnosed as renal colic.

• Hematuria is absent in 15% of patients with symptomatic nephrolithiasis.

Scope and Outline

Renal colic is defined as severe, spasmodic pain caused by the impaction or passage of a calculus in the renal pelvis or ureter. Symptomatic nephrolithiasis will develop in approximately 15% of the U.S. population during their lives ¹; the majority of these patients seek treatment in the emergency department (ED).

Pathophysiology

Renal stones form when the urine becomes supersaturated with calcium, oxalate, cystine, uric acid, or struvite. Hypercalciuria accounts for the development of 60% of calculi and results from increased intestinal absorption, decreased renal tubular reabsorption, or excessive bone resorption of calcium. Decreased urine output can further promote calculus formation as a result of reductions in citrate, magnesium pyrophosphate, and other inhibitors of urine crystallization. Table 112.1 describes features of the five main types of renal calculi.

Table 112.1 The Five Main Types of Renal Calculi

Stone impaction may occur anywhere along the path of the genitourinary tract. The resultant ureteral obstruction can shift hydrostatic pressure and cause blood flow to be redistributed to the opposite renal artery. The overall rate of glomerular filtration decreases as renal excretion becomes a task of the unaffected kidney. A transient increase in serum creatinine may follow this decrease in the glomerular filtration rate.

Although an initial rise in creatinine may quickly resolve, irreversible kidney damage can begin to occur after 7 days of complete obstruction.^3,⁴ Prolonged obstruction impairs recoverable kidney function over time,^4,⁵ but case reports show that some recovery may be possible for up to 150 days.^5,⁶

Ureteral obstruction is primarily determined by calculus size. Most stones smaller than 5 mm in diameter will pass spontaneously (90%), whereas passage of stones larger than 8 mm is unlikely (5%). Table 112.2 compares ureteral stone size with the percent likelihood of spontaneous passage.

Table 112.2 Renal Calculus Size and Likelihood of Spontaneous Passage

STONE SIZE (DIAMETER)	PERCENT LIKELIHOOD OF SPONTANEOUS PASSAGE
<5 mm	90
5-8 mm	15
>8 mm	5

Anatomy

Stone impaction most commonly occurs at the ureterovesical junction, the narrowest part of the genitourinary tract. Other common areas of impaction include the ureteropelvic junction (where the renal pelvis narrows from 1 cm down to 3 mm) and the pelvic brim (where the ureter arches anteriorly across the iliac vessels) (Fig. 112.1).

Fig. 112.1 Common sites of renal calculus impaction.

Clinical Presentation

History

Renal colic is classically manifested as a sudden onset of excruciating, intermittent flank pain that radiates to the groin. This swift onset of pain is often accompanied by a deeper flank ache, nausea, and vomiting. The severe, spasmodic pain of renal colic is thought to be caused by hyperperistalsis of smooth muscle from the calices to the ureter. The dull, deep, aching pain reflects ureteral obstruction and distention of the renal capsule.

The location of the ureteral calculus determines the symptoms, as outlined in Table 112.3.

Table 112.3 Ureteral Calculus Location and Associated Symptoms

LOCATION OF CALCULUS	SYMPTOMS
Renal pelvis or calyx	Deep flank ache
Proximal or middle part of the ureter	Severe flank pain radiating to the groin
Distal end of the ureter	Flank discomfort and/or low abdominal pain
Bladder	Dysuria, frequency, urgency, retention, suprapubic discomfort

Physical Examination

Patients with renal colic typically appear uncomfortable and are commonly described as “writhing” on the gurney. Findings on the abdominal examination are generally unremarkable, although thin patients with distal ureteral stones and obstruction may exhibit some tenderness. Tenderness at the costovertebral angle can develop as a result of worsening hydronephrosis; this sign is mild or absent early in the course of the disease. Abnormal findings on physical examination should raise suspicion for alternative diagnoses, as reviewed in Table 112.4.

Table 112.4 Physical Examination Findings and Potential Alternative Diagnoses

FINDING	CONSIDERATION
Vital Signs
Fever	Infected stone, pyelonephritis, perinephric abscess
Hypotension	Sepsis, abdominal aortic aneurysm
Abdomen
Bruit	Abdominal aortic aneurysm, renal artery stenosis
Pulsatile mass	Abdominal aortic aneurysm
Pronounced costovertebral angle tenderness	Pyelonephritis
Lower abdominal or pelvic tenderness	Ectopic pregnancy, appendicitis, pelvic inflammatory disease, tuboovarian abscess, ovarian torsion
Genitourinary
Testicular tenderness	Torsion, epididymitis, orchitis
Mass	Hernia, cancer
Pulmonary
Focal findings	Lobar pneumonia
Cardiovascular
Asymmetric lower extremity pulses	Abdominal aortic aneurysm
Skin
Vesicular rash	Herpes zoster

Differential Diagnosis

Many disease processes can mimic symptomatic nephrolithiasis. Abdominal aortic aneurysm, aortic dissection, renal artery dissection, and renal infarction are the most lethal conditions that may manifest similar to renal colic. In one study, abdominal aortic aneurysms were initially misdiagnosed as kidney stones in approximately 20% of patients older than 60 years.⁷ Box 112.2 lists the differential diagnosis for renal colic.

Diagnostic Testing

Laboratory Tests

ED imaging (Table 112.5) is used to confirm the diagnosis of nephrolithiasis, evaluate stone size, identify obstruction, and exclude alternative diagnoses. Patients with decreased renal reserve (solitary kidney, uncontrolled diabetes mellitus, uncontrolled hypertension), concurrent infection, first occurrence of stone disease, advanced age, and prolonged or unrelenting symptoms should undergo imaging during their initial evaluation. Indications for emergency imaging in cases of suspected renal colic are summarized in Table 112.6.

Table 112.5 Imaging Modalities for Detection of Nephrolithiasis

Table 112.6 Indications for Diagnostic Imaging of Patients with Suspected Renal Colic

FINDING	INDICATION FOR DIAGNOSTIC IMAGING
Solitary kidney, uncontrolled diabetes,* uncontrolled hypertension*	To exclude obstruction in a patient with decreased renal reserve
Advanced age	To exclude alternative diagnoses, especially vascular disease
Concurrent infection	If concurrent with obstruction, a urologist should be involved to evaluate the need for intervention
Prolonged symptoms	To evaluate for prolonged obstruction, which may cause renal impairment
Refractory symptoms, first occurrence*	To exclude alternative diagnoses, especially ischemia or infarction

^* Relative indication.

Helical Computed Tomography

Noncontrast helical computed tomography (CT) of the abdomen and pelvis is the preferred imaging modality for the evaluation of patients with suspected nephrolithiasis. CT imaging for renal stones can be performed without contrast material, demonstrates both high sensitivity (94% to 100%) and specificity (96% to 100%),¹¹^–¹⁵ and allows alternative diagnoses to be simultaneously identified.^15,¹⁶ Sagittal images are obtained at 5-mm intervals from the top of the kidney to the bottom of the bladder (Figs. 112.2 and 112.3).

Fig. 112.2 Noncontrast renal protocol computed tomography scan showing moderate hydronephrosis of the left renal pelvis (arrow).

Fig. 112.3 Noncontrast renal protocol computed tomography scan showing a stone at the left ureteropelvic junction (arrow).

Intravenous Pyelography

Intravenous pyelography (Fig. 112.4) has a sensitivity of 52% to 85% and specificity of 97% to 100% for detection of ureteral calculi.^11,^17,¹⁸ It provides a visual interpretation of renal function, as well as genitourinary anatomy. The earliest sign of ureteral obstruction on an intravenous pyelogram is a delayed nephrogram; other abnormal findings include a “standing column” (the entire ureter seen on one image; Fig. 112.5), hydroureter, hydronephrosis, contrast cutoff at the point of impaction, and extravasation of contrast material. The use of intravenous pyelography is limited by the need for contrast material, decreased sensitivity in comparison with helical CT, and the length of time required to obtain multiple delayed images.

Fig. 112.4 Normal findings on an intravenous pyelogram.

Fig. 112.5 Intravenous pyelogram showing the entire left ureter in one view.

This is known as a standing column and is caused by lack of ureteral peristalsis because of a ureteral stone.

Sonography

Ultrasonography is a useful modality for identifying hydronephrosis caused by ureteral obstruction (Fig. 112.6). Advantages include its ease of use and rapid acquisition of diagnostic images at the bedside without the need for contrast agents or radiation. It is the imaging technique of choice for the evaluation of suspected renal colic in pregnancy. Ultrasonography is limited by false-negative results, which occur in patients with small calculi that do not cause significant obstruction or hydronephrosis. The sensitivity and specificity of ultrasonography for the diagnosis of urologic stone disease is 66% to 93% and 83% to 100%, respectively.¹⁸^–²⁰

Fig. 112.6 Renal ultrasound showing moderate hydronephrosis.

Plain Radiography

The utility of plain radiography (kidney-ureter-bladder [KUB] projection performed in the supine position) is dependent on the radiodensity of the suspected kidney stone. Although 90% of stones are radiopaque (Fig. 112.7), uric acid and cystine calculi are radiolucent. KUB imaging is limited technically by overlying soft tissue, air, and bone; low sensitivity (58% to 62%) and specificity (67% to 69%) are observed in clinical practice.^21,²² The combination of ultrasonography and KUB radiography improves the usefulness of these imaging modalities. Studies that used both ultrasound and plain radiography for the detection of nephrolithiasis demonstrated a sensitivity and specificity of 89% and 100%, respectively, when both tests were positive²⁰ and a sensitivity and specificity of 95% and 67%, respectively, when either test was positive.²³

Fig. 112.7 Kidney-ureter-bladder radiograph showing a large kidney stone on the right (arrow).

Treatment

Pharmacologic Management

Patients with renal colic will probably require immediate pain control. Several options are available for rapid analgesia.

Nonsteroidal Antiinflammatory Drugs

Nonsteroidal antiinflammatory drugs (NSAIDs) decrease ureteral spasm by inhibiting prostaglandin synthesis. Renal blood flow may be reduced when NSAIDs are administered in the setting of ureteral obstruction,²⁴ thereby improving symptoms through a decrease in urine production and ureteric pressure. Ketorolac (Toradol) (30 mg intravenously or 60 mg intramuscularly) has efficacy equivalent to the oral administration of 800 mg of ibuprofen, although the latter may be less well tolerated in patients with concomitant nausea.

Some urologists debate the routine use of NSAIDs for the treatment of nephrolithiasis because these medications may promote bleeding after the placement of a ureteral stent. Data to support such observations are inconclusive.

Opiates

Intravenous narcotics provide adequate relief of symptoms for most patients with renal colic. Opiates have similar analgesic effects at equivalent dosing. Although meperidine (Demerol) demonstrates smooth muscle relaxation when tested in vitro,²⁵ this spasmolytic effect does not appear to improve its clinical utility in therapy for renal colic.²⁶ Given the potential for drug interactions with meperidine, preferred opiates for ED use include hydromorphone (0.015 mg/kg) and morphine (0.1 mg/kg starting dose).

Documentation

Patient’s age

Onset, location, and duration of pain

Urinalysis results

Medical decision making for imaging

Medical decision making for disposition

Discharge instructions and return precautions

Follow-up within 7 days

Tips and Tricks

A young, healthy patient with the typical findings of renal colic, a history of previous nephrolithiasis, no signs of infection, and easily managed symptoms may be discharged with analgesics, antiemetics, and a urine strainer for follow-up within 7 days.

All other patients require evaluation of the need for imaging and possible urology consultation.

Red Flags

Patients older than 60 years: Consider a vascular cause of their pain.

Signs of infection: Exclude concurrent obstruction.

Large calculi: 5-mm stones have a 50% chance of passing; stones larger than 8 mm have a 5% chance of passing.

Multiple studies have shown that both NSAIDs and opiates are effective and appropriate treatments of renal colic.²⁴^–³¹ One metaanalysis of 19 studies showed that NSAIDs and opiates are equally effective in the acute management of renal colic symptoms.²⁸ Many experts recommend the use of NSAIDs followed by opiates for continued pain.