A 32-year-old female, 13 weeks gestation, with history of nephrolithiasis presented with left-sided flank pain and low-grade fever. Ultrasonography showed (a) normal right kidney, (b) left hydronephrosis, (c) right ureteral jet visualized with color-flow Doppler, and (d) 2.7 mm calcification seen at left ureterovesical junction, with no ureteral jet. The patient was taken to the operating room for cystoscopic insertion of left ureteral stent under spinal anesthesia. She tolerated the procedure well and clinically improved postoperatively
If a stone is not visualized on ultrasound and there is still suspicion of a stone, other imaging modalities may be used. Historically, intravenous pyelography has been considered the second-line imaging test in the pregnant patient with renal colic. Single-shot pyelography involves a single radiograph taken 30 min after administration of intravenous contrast. One study that involved 57 pregnant women with symptomatic urolithiasis found that single-shot intravenous pyelogram was able to detect stones in 8 of the 14 patients with a negative ultrasound . One radiograph exposes the fetus to about 0.3 rads, well below the threshold of 5 rads reported by Gomes et al. .
MRI has also been used to evaluate pregnant patients with renal colic; however, the accuracy, sensitivity, and specificity of MRI in diagnosing ureteral stones in pregnancy have not been established. According to the American College of Radiology, MRI poses no known risks to the fetus during pregnancy . It is important to note, however, that gadolinium-based contrast should not be given as it crosses the placenta and is considered a category C substance in pregnancy. Stones, especially small stones, are not well-visualized with MRI and are instead characterized as filling defects in the collecting system. Other MRI findings consistent with the presence of obstructive urolithiasis are renal edema and perirenal or periureteral fluid . Mullins et al. described the use of half-Fourier single-shot turbo spin-echo (HASTE) protocol MRI, which rapidly acquires images of the upper urinary tract without the need of intravenous contrast . In HASTE magnetic resonance urography (MRU), upper urinary tract obstruction is seen on T2-weighted imaging as perinephric stranding or rim enhancement of the renal capsule. In a small study of nine pregnant patients with renal colic and a nondiagnostic renal ultrasound, HASTE MRU was able to identify four ureteral stones that were not seen previously. HASTE MRU has been studied in nonpregnant patients with renal colic and has been found to have 84% sensitivity and 100% specificity when using CT as the reference standard .
Low-dose CT protocols have been developed in hopes to improve the detection of urolithiasis in pregnant women. White et al. studied 20 patients with renal colic who had ultrasound showing either normal kidneys or hydronephrosis consistent with pregnancy . Each patient underwent CT scan with low-dose protocol, and urolithiasis was detected in 13 patients, of whom 9 required urologic intervention. The average exposure to the fetus with low-dose CT is 0.7 rads, compared to 1.1 rads with conventional stone hunt protocol CT. In a more recent study, the same authors compared the accuracy of renal ultrasound, MRU, and low-dose CT in 51 pregnant patients who underwent ureteroscopy for high suspicion of symptomatic urolithiasis. The authors found that the positive predictive values of renal US, MRU, and low-dose CT were 77%, 80%, and 95.8%, respectively . Low-dose CT seems to have low fetal risk and yields relatively reliable results and can be especially useful when there is hesitation to perform an invasive procedure without a definite diagnosis. Ultimately, because of the unknown long-term effects of radiation to the fetus, a thorough discussion should be undertaken with the patient regarding the potential risks of radiation and the risks of urologic intervention.
Pregnant patients with symptomatic urolithiasis should initially be managed conservatively with hydration and pain control, unless the patient presents with indications for immediate urinary drainage (i.e., bilateral obstruction or infection). Spontaneous passage rates have been reported from 64% to 84% [3, 4, 33]. Conversely, Burgess and colleagues contend that previous studies may have overestimated spontaneous passage rates, possibly due to misdiagnosis of urolithiasis as the cause of physiologic hydronephrosis. In their study, they established stone presence by imaging, surgical extraction, or visual confirmation and found a 48% spontaneous passage rate over a mean follow-up period of 51 months . Their findings underscore the importance of accurately determining the presence of urolithiasis when treating a pregnant patient with renal colic, whether it means evaluation with alternative imaging or pursuing urologic intervention after giving the patient a fair chance to pass the stone.
In nonpregnant patients, medical expulsion therapy (MET) includes hydration, analgesia, and administration of an alpha-blocker. In a large meta-analysis, alpha-blockers were found to facilitate passage of ureteral stones as it results in a higher stone-free rate and a shorter time to stone expulsion . Alpha-blockers (specifically tamsulosin) have also been found to be more effective than the calcium channel blocker nifedipine in facilitating expulsion of distal ureteral calculi . Tamsulosin is considered a category B medication for pregnant patients, while nifedipine is a category C drug. The safety of tamsulosin in MET for pregnant women has only recently been studied. Bailey et al. studied 27 pregnant patients who received tamsulosin for MET and found that the use of tamsulosin was not associated with adverse maternal or fetal events .
When conservative management fails, several treatment options are available, but none have been established as superior to another. The obstructed collecting system can be successfully drained with an indwelling ureteral stent or a percutaneous nephrostomy tube; however, both have shortcomings. Cystoscopy with insertion of a ureteral stent can be performed with minimal fluoroscopy or under ultrasound guidance with local anesthesia and intravenous sedation . However, because of physiologic hypercalciuria and hyperuricosuria that occur during pregnancy, there is an increased risk of stent encrustation, necessitating more frequent ureteral stent exchanges at about 4–6-week intervals until the baby is delivered . If the woman was to require a stent early in pregnancy, she would require multiple stent exchanges during the course of the pregnancy. Aside from the morbidity of frequent stent exchanges, having an indwelling stent in itself increases the risk of bacteriuria, urinary tract infection, stent colic, and stent migration which poses risks to the pregnancy and patient’s quality of life [9, 38].
Placement of a percutaneous nephrostomy tube is an alternative option for pregnant women who need urgent urinary drainage. It is performed under ultrasound guidance with local anesthesia and, if necessary, intravenous sedation. Just as with ureteral stents, these drainage tubes can become calcified and obstructed. Kavoussi et al. found that five of six pregnant women treated with percutaneous nephrostomy required frequent tube exchanges due to occlusion of the nephrostomy tubes . Two patients required removal of the tubes during their pregnancy due to fever and pain. Khoo et al. had similar findings and had one of eight patients become septic due to occlusion of the nephrostomy . Not only can nephrostomy tubes become occluded, but they can also cause discomfort and inconvenience for the patient as it is an external tube. However, nephrostomy tube exchanges have advantages over stents as they typically do not require anesthesia. These issues should be discussed with the patient when counseling them regarding the treatment options.
Placement of ureteral stents and nephrostomy tubes are both temporizing measures, and the patient will eventually need a definitive procedure to remove the stone after or sometimes during the course of their pregnancy. Although ureteroscopy has been typically performed under general anesthesia, improvements in the ureteroscopes have made this procedure possible to perform with local or epidural anesthesia. Scarpa et al. described performing rigid ureteroscopy with smaller-caliber ureteroscopes (7 French and 9.5 French) on 15 pregnant patients for symptomatic ureteral stones . Five of those patients required no anesthesia at all, while the remaining ten required only neuroleptic analgesia (propofol or fentanyl). None of the patients required ureteral dilation, and none suffered any major urologic or obstetric complications. Stone fragmentation can be safely performed with the holmium:YAG laser or a pneumatic lithotripter with similar results [42, 43]. The success rate, in terms of stone clearance, of ureteroscopy during pregnancy is relatively high, ranging from 85% to 89% for ureteral calculi and even 81% for proximal stones [42–44]. When compared with percutaneous nephrostomy and ureteral stenting, ureteroscopy had less postoperative complications than the other procedures but required a longer hospital stay (5.6 days compared to 0.6 days for ureteral stenting and 3 days for percutaneous nephrostomy) . Overall, the added risks of ureteroscopy in pregnant women are small, making ureteroscopy a feasible option if the patient requests or requires definitive stone management during pregnancy.
The timing of intervention depends on the stability of the patient, as well as the gestational age of the fetus. If the patient presents with signs of instability such as fever, sepsis, or threatened labor, prompt urinary drainage with either percutaneous nephrostomy or internal ureteral stent is indicated. At earlier stages in pregnancy, percutaneous nephrostomy is favored over ureteral stents considering the patient will likely need tube exchanges every 4–6 weeks due to high rates of stent encrustation in pregnancy . Nephrostomy tube exchanges can be done without anesthesia, while ureteral stent exchanges typically require intravenous sedation or epidural anesthesia. In stable patients, ureteroscopy with lithotripsy can be a safe treatment option during any trimester .
Other methods of definitive stone management that are used in the nonpregnant population, such as extracorporeal shock wave lithotripsy (ESWL) and percutaneous nephrolithotomy (PNL), are not accepted treatment modalities in the pregnant patient. Although there has been a case report of a successful ESWL in a pregnant patient, pregnancy is widely regarded as a contraindication to the procedure . PNL in pregnancy has only recently been described in literature. Basiri et al. published a case series of three pregnant patients who failed conservative management and required percutaneous stone extraction for large renal stones . The procedure was performed under spinal anesthesia in the supine position, and percutaneous access was obtained under ultrasound guidance. Despite the success of this case report, the inherent risks of percutaneous nephrolithotomy currently outweigh the potential benefits in the pregnant patient, and PNL should be deferred until the postpartum period.
The state of pregnancy introduces additional hurdles in the diagnosis and management of renal and ureteral calculi. Although new imaging modalities have been developed in recent years in hopes of more accurate diagnosis, the reluctance of patients and physicians alike to experiment with unknown risks has prevented widespread usage of newer technology. Luckily, a large proportion of pregnant women with symptomatic nephrolithiasis can be treated conservatively. However, for patients who do require more invasive treatment, the options must be considered thoroughly as each has its own set of risks and benefits.