400 CHAPTER 8 Stone disease
Bladder stones
Composition
Bladder stones consist of struvite (i.e., they are infection stones) or uric acid (in noninfected urine).
Adults
Bladder calculi are predominantly a disease of men aged >50 and with bladder outlet obstruction due to benign prostatic enlargement (BPE). They also occur in the chronically catheterized patient (e.g., spinal cord injury patients), in whom the chance of developing a bladder stone is 25% over 5 years (similar risk whether urethral or suprapubic location of the stone).1
Children
Bladder stones are still common in Thailand, Indonesia, North Africa, the Middle East, and Burma. In these endemic areas they are usually composed of a combination of ammonium urate and calcium oxalate. A low-phos- phate diet in these areas (a diet of breast milk and polished rice or millet) results in high peaks of ammonia excretion in the urine.
Symptoms
Bladder stones may be symptomless (incidental finding on KUB X-ray or bladder ultrasound or on cystoscopy) and is the common presentation in spinal patients who have limited or no bladder sensation.
In the neurologically intact patient, suprapubic or perineal pain, hematuria, urgency and/or urge incontinence, recurrent UTI, and LUTS (hesitancy, poor flow) may occur.
Diagnosis
If you suspect a bladder stone, it will be visible on KUB X-ray or renal ultrasound (Fig. 8.15).
Treatment
Most stones are small enough to be removed cystoscopically (endoscopic cystolitholapaxy), using stone-fragmenting forceps for stones that can be engaged by the jaws of the forceps and EHL or pneumatic lithotripsy for those that cannot. Large stones (see Fig. 8.15) can be removed by open surgery (open cystolitholapaxy).
1 Ord J (2003). Bladder management and risk of bladder stone formation in spinal cord injured patients. J Urol. 170:1734–1737.
BLADDER STONES 401
Figure 8.15 A bladder stone.
402 CHAPTER 8 Stone disease
Management of ureteric stones in pregnancy
While hypercalciuria and uric acid excretion increase in pregnancy (predisposing to stone formation), so do urinary citrate and magnesium levels (protecting against stone formation). The incidence of ureteric colic is thus the same as in nonpregnant women. 1
Ureteric stones occur in 1 in 1500–2500 pregnancies, mostly during the second and third trimesters. They are associated with a significant risk of preterm labor,2 and the pain caused by ureteric stones can be difficult to distinguish from other causes.
The hydronephrosis of pregnancy
Ninety percent of pregnant women have bilateral hydronephrosis from weeks 6–10 of gestation and up to 2 months after birth (smooth muscle relaxant effect of progesterone and mechanical obstruction of ureter from the enlarging fetus and uterus). Hydronephrosis is taken as surrogate evidence of ureteric obstruction in nonpregnant individuals, but because it is a normal finding in the majority of pregnancies, its presence cannot be taken as a sign of a possible ureteric stone.
Ultrasound is unreliable for diagnosing the presence of stones in pregnant (and in nonpregnant) women (sensitivity, 34%—i.e., it misses 66% of stones; specificity, 86%—i.e., false-positive rate of 14%).3
Differential diagnosis of flank pain in pregnancy
This includes ureteric stone, placental abruption, appendicitis, pyelonephritis, and all the other (many) causes of flank pain in nonpregnant women.
Diagnostic imaging studies in pregnancy
Exposure of the fetus to ionizing radiation can cause fetal malformations, malignancies in later life (leukemia), and mutagenic effects (damage to genes causing inherited disease in the offspring of the fetus). Fetal radiation doses during various procedures are shown in Table 8.4.
While the recommended maximum radiation levels shown in Table 8.4 are well above those occurring during even CT scanning, and a dose of 50 mGy or less is regarded as safe, every effort should be made to limit exposure of the fetus to radiation. Pregnant women may be reassured that the risk to the unborn child as a consequence of radiation exposure is likely to be minimal.
1 Coe FL, Parks JH, Lindhermer MD (1978). Nephrolithiasis during pregnancy. N Engl J Med 298:324–326.
2 Hendricks SK (1991). An algorithm for diagnosis and therapy of urolithiasis during pregnancy
Surg Gyne Obst 172:49–54.
3 Stothers L, Lee LM (1992). Renal colic in pregnancy. J Urol 148:1383–1387.
4 Hellawell GO, Cowan NC, Holt SJ, Mutch SJ (2002). A radiation perspective for treating loin pain in pregnancy by double-pigtail stents. Br J Urol Int 90:801–808.
MANAGEMENT OF URETERIC STONES IN PREGNANCY 403
Table 8.4 Fetal radiation dose after various radiological investigations
Procedure |
Fetal dose |
Risk of inducing cancer |
|
(mGy) (mean) |
(up to age 15 years) |
|
|
|
KUB X-ray |
1.4 |
— |
IVP 6 shot |
1.7 |
1 in 10,000 |
IVP 3 shot |
— |
— |
CT: abdominal |
8 |
— |
CT: pelvic |
25 |
— |
Fluoroscopy for JJ stent |
0.4 |
1 in 42,000 |
insertion |
|
|
|
|
|
Radiation doses of <100 mGy are very unlikely to have an adverse effect on the fetus.4 In the United States, the National Council on Radiation Protection has stated that “fetal risk is considered to be negligible at <50 mGy when compared to the other risks of pregnancy, and the risk of malformations is significantly increased above control levels at doses >150 mGy.”5
The American College of Obstetricians and Gynecologists has stated that “X-ray exposure to <50 mGy has not been associated with an increase in fetal anomalies or pregnancy loss.”6
Plain radiography and IVP
These have limited usefulness (fetal skeleton and the enlarged uterus obscure ureteric stones; delayed excretion of contrast limits opacification of ureter; theoretical risk of fetal toxicity from the contrast material).
CTU
CTU is a very accurate method for detecting ureteric stones, but most radiologists and urologists are unhappy to recommend this form of imaging in pregnant women.
MRU
The American College of Obstetricians and Gynecologists and the U.S. National Council on Radiation Protection state that “although there is no evidence to suggest that the embryo is sensitive to magnetic and radiofrequency at the intensities encountered in MRI, it might be prudent to exclude pregnant women during the first trimester.”5,6
MRU can thus potentially be used during the second and third trimesters, but not during the first trimester. It involves no ionizing radiation. It is
5 National Council on Radiation Protection and Measurement (1997). Medical radiation exposure of pregnant and potentially pregnant women. NCRP Report no. 54. Bethesda, MD: NCRPM.
6 American College of Obstetricians and Gynecologists Committee on Obstetric Practice (1995). Guidelines for Diagnostic Imaging During Pregnancy. ACOG Committee Opinion no. 158. Washington DC: ACOG.
7 Roy C (1996). Assessment of painful ureterohydronephrosis during pregnancy by MR urography. Eur Radiol 6:334–338.
404 CHAPTER 8 Stone disease
very accurate (100% sensitivity for detecting ureteric stones7) but expensive, and not readily available in most hospitals, particularly after hours.
Management
Most (70–80%) stones will pass spontaneously. Pain relief is with opiatebased analgesics; avoid NSAIDs (can cause premature closure of the ductus arteriosus by blocking prostaglandin synthesis).
Indications for intervention are the same as in nonpregnant patients (pain refractory to analgesics, suspected urinary sepsis [high fever, high white count], high-grade obstruction and obstruction in a solitary kidney).
Options for intervention
Options depend on the stage of pregnancy and on local facilities’ equipment and expertise:
-JJ stent urinary diversion
-Nephrostomy urinary diversion
-Ureteroscopic stone removal
Aim to minimize radiation exposure to the fetus and to minimize the risk of miscarriage and preterm labor.
General anesthesia can precipitate preterm labor, and many urologists and obstetricians will prefer temporizing options, such as nephrostomy tube drainage or JJ stent placement, over operative treatment in the form of ureteroscopic stone removal.
Chapter 9 |
405 |
|
|
Upper tract obstruction, flank pain, hydronephrosis
Hydronephrosis 406
Management of ureteric strictures (other than UPJ obstruction) 410
Pathophysiology of urinary tract obstruction 414 Physiology of urine flow from kidneys to bladder 416 Ureter innervation 417