Материал: Oxford American Handbook of Urology ( PDFDrive )

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

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.

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

406 CHAPTER 9 Upper tract obstruction

Hydronephrosis

Hydronephrosis is dilatation of the renal pelvis and calyces (Fig. 9.1). When combined with dilatation of the ureters it is known as hydroureteronephrosis.

Obstructive nephropathy is damage to the renal parenchyma resulting from obstruction to the flow of urine anywhere along the urinary tract.

Dilatation of the renal pelvis and calyces can occur without obstruction and thus hydronephrosis should not be taken to necessarily imply the presence of obstructive uropathy.

Ultrasound

•False negative (i.e., obstruction present, no hydronephrosis)—acute onset of obstruction; in the presence of an intrarenal collecting system; with dehydration; misdiagnosis of dilatation of the calyces as renal cortical cysts (in acute ureteric colic, ultrasonography fails to detect hydronephrosis in up to 35% of patients with proven acute obstruction on IVP)

•False positive (i.e., hydronephrosis, no obstruction)—capacious extrarenal pelvis; parapelvic cysts; vesicoureteric reflux; high urine flow

Diagnostic approach to the patient with hydronephrosis

Hydronephrosis may present either as an incidental finding on an ultrasound or CT done because of nonspecific symptoms or it may be identified in a patient with a raised creatinine or presenting with flank pain.

Symptoms, if present, will depend on the rapidity of onset of obstruction of the kidney (if that is the cause of the hydronephrosis); whether obstruction is complete or partial, unilateral or bilateral; and whether the obstruction to the ureter is extrinsic to the ureter or within its lumen.

Causes of hydronephrosis are listed in Box 9.1.

History

•Severe flank pain suggests a more acute onset of obstruction and, if very sudden in onset, a ureteric stone may well be the cause. Pain induced by a diuresis (e.g., following consumption of alcohol) suggests a possible UPJ obstruction (See Chapter 7, p. 346).

•Anuria (the symptom of bilateral ureteric obstruction or complete obstruction of a solitary kidney)

•If renal function is impaired, symptoms of renal failure may be present (e.g., nausea, lethargy, anorexia).

•Extrinsic causes of obstruction (e.g., compression of the ureters by retroperitoneal malignancy) usually have a more insidious onset, whereas intrinsic obstruction (ureteric stone) is often present with severe pain of very sudden onset.

•An increase in urine output may be reported by the patient that is due to poor renal concentrating ability.

•Obstruction in the presence of bacterial urinary tract infection—signs and symptoms of pyelonephritis (flank pain and tenderness, fever) or sepsis