MRU involves no ionising radiation and can be done with the administration of contrast (Fig. 8.2). It is very accurate, with one group reporting a sensitivity for detecting ureteric stones of 100% (Roy et al. 1996). However, MRU is expensive, and not readily available in most hospitals, particularly after 5 o'clock. As MR scanners become more widespread, it is likely that this imaging modality will be used increasingly to establish a diagnosis in pregnant women with flank pain.
FIGURE 8.2. Magnetic resonance urography.
156 J. REYNARD
MANAGEMENT OF URETERIC STONES IN PREGNANT WOMEN
The majority (70-80%) of ureteric stones in pregnant women pass spontaneously (Stothers et al. 1992. Of those that do not pass and require temporizing treatment with nephrostomy tube drainage or JJ stents, many pass spontaneously postpartum. Opiate-based analgesics are used for pain relief and oral and intravenous fluids for hydration. Nonsteroidal antiinflammatory drugs (NSAIDs) should be avoided because they can cause premature closure of the ductus arteriosus by blocking prostaglandin synthesis.
The indications for intervention are essentially the same as in nonpregnant patients and include pain refractory to analgesics, suspected urinary sepsis (high fever, high white count), high-grade obstruction, and obstruction in a solitary kidney.
Options for intervention are JJ stent urinary diversion, nephrostomy urinary diversion, or ureteroscopic stone removal. Which option you use depends on how advanced the pregnancy is, and on local facilities and expertise. Management of cases requiring active intervention should aim to minimize radiation exposure to the fetus, and to minimize the risk of miscarriage and preterm labour. General anaesthesia can precipitate preterm labour (Duncan et al. 1986), and with this in mind many urologists and obstetricians err on the side of temporizing options such as nephrostomy tube drainage or JJ stent placement, rather than on operative treatment in the form of ureteroscopic stone removal.