Urological perspectives of flank pain during pregnancy

Background
There are various causes of flank pain during pregnancy, either singly or in combination. These may be urological and / or non-urological in aetiology. The non- urological causes include musculoskeletal, neurological and gastrointestinal conditions. The latter causes are beyond the scope of this article; however it is important that the managing obstetrician and midwife bear these differentials in mind.

The commoner urological diagnoses for loin pain during pregnancy include urolithiasis, pyelonephritis, hydronephrosis and the ‘loin pain haematuria syndrome’. Pyelonephritis and urolithiasis account for up to 50% of these cases¹.

Kidney, ureter and bladder (KUB) ultrasound scan is the usual investigation to exclude hydronephrosis and obstructive nephropathy due to calculus disease. KUB ultrasound is sensitive and specific for renal stones: 81% and 100%; and between 93% and 100% for hydronephrosis. Its sensitivity to detect ureteric stones and hydroureter is however lower (46% and 50% respectively). Thus in such cases, the addition of X-ray KUB would be of benefit².

Xray KUB is not strictly contraindicated in pregnancy, but should be undertaken only if there are no alternatives to making a diagnosis or in a patient in whom symptoms are unrelenting.

Other investigations should be individualised, and may include urine microscopy, urine and blood cultures, IVU (15 mins single shot) and MRI scans, depending on patients’ presentation and identified co-morbidities.

The management of flank pain during pregnancy is largely medical in over 80% of women, with about 5% will requiring surgical intervention in terms of a nephrostomy tube, antegrade or retrograde JJ stent insertion, and very rarely, a ureteroscopy with or without stone fragmentation.

Pyelonephritis
Routine testing for asymptomatic bacteruria (AB) in pregnancy is now standard practice, and the treatment of AB has reduced the incidence of pyelonephritis in pregnancy³. Pyelonephritis is caused by infection within the renal pelvis, with or without infection of the renal parenchyma. Escherichia coli is the commonest bacteria more than 87% of cases, this bacterial ascent complicating 1 – 2% of all pregnancies, resulting in significant foetal and maternal morbidity. A recent cohort study found that 21% of cases occur during the first trimester⁴.

Typical presentation includes flank pain, vomiting, rigors, and fever. Yet, urinary symptoms may be minimal or absent⁵. Laboratory testing for culture and sensitivity should be performed in all pregnant women with suspected pyelonephritis.

There is no clear consensus as per antibiotic of choice or duration of treatment, however, for pregnant women not requiring admission, i.e. apyrexial women who may be managed in primary care, treatment with Cefalexin 500mg twice daily for between 10 and 14 days is advised, together with Antipyretic-analgesics and hydration. The Health Protection Agency recommends Ciprofloxacin or Co-Amoxiclav for the empirical treatment of acute pyelonephritis. This can be modified later according to sensitivity. Cefalexin has a reduced spectrum of activity, but is considered to be safer during pregnancy. Expert consensus recommends hospital admission for those unable to take fluids and medications orally, or those who have signs of sepsis and fail to improve within 24 hours of starting antibiotics⁶.

Low-dose antibiotic prophylaxis is recommended for recurrent infections with no treatable cause.

Urolithiasis
Urolithiasis is challenging in terms of diagnosis and management during pregnancy. It presents a risk both to the mother and the foetus, and can induce preterm labour in up to 40% of cases; it is nevertheless uncommon⁷. Studies have shown that there is no significant difference in the incidence of urinary calculi disease in pregnancy when compared to the non-pregnant state. The incidence of symptomatic urinary calculi in pregnancy ranges from between 1 in 1500 to 1 in 2500^8,9. Even though there is a two- to three-fold increase in urinary calcium excretion caused by absorptive hypercalciuria and serum oxalate super saturation as a result of increased production of 1,25-dihydroxycholecalciferol by the placenta, there is no increased incidence.

This increased calcium excretion is probably counter-balanced by an increased secretion of urinary stone inhibitors such as citrates, and glycosaminoglycans, and dilution from hypervolaemia of pregnancy⁷.

Patients with acute ureteric obstruction may present with symptoms of abdominal / flank pain, hematuria, nausea and vomiting, dysuria, polyuria, voiding difficulties and a fever. Initial investigations should include the following; white cell count, serum electrolytes, urine microscopy, culture and sensitivity, and ultrasonography of the urinary tract^{1, 10, 11, 12}. The accuracy of ultrasound scan in predicting the presence of a stone improved when there is the absence of ureteric jet, and an elevated resistive index³. Expectant management with pain relief (an analgesic and an antispasmodic) is effective in 63 to 85% of patients³.

The indications for surgical intervention include:

P – persistent pain,
I – infection,
D – deteriorating renal function especially in a solitary kidney, and
O – persistent Obstruction.

Traditionally, the options of treatment of obstructing renal calculi during pregnancy included percutaneous nephrostomy (PCN) tube placement, or double JJ stent insertion, either antegrade or retrograde. The stones either pass spontaneously or are removed post-partum. There is now a body of evidence to show that uretero-renoscopic stone extraction in selected patients is not only safe, but a very effective modality of treatment for this group of patients.

Several studies have indicated that there is no increased complication rate compared to the normal population, and therefore should be considered as an appropriate first line therapy in pregnant patients with stone disease^{13, 14}.

Hydronephrosis
Gestational hydronephrosis is a physiological condition occurring in 90% of pregnant women, commencing from between the 6th and 11th week of pregnancy, and resolving at about 6 weeks post-partum. It is thought to occur as a result of hormonal relaxation of ureteric smooth muscles and mechanical compression of the ureters by the gravid uterus¹⁵. The right side is more commonly affected than the left, and the following theories account for this. Dextrorotation of the uterus and sigmoid colon with a cushioning effect on the left ureter, results in reduced compression on the left, and the congestion of the right ovarian veins lead to a higher right sided incidence¹.

The clinical significance of symptomatic hydronephrosis in pregnancy is its possible association with imminent complications. These include ureteric obstruction and pain, infection and deteriorating renal function. These may lead to maternal sepsis and threatened miscarriage or preterm labour. Asymptomatic hydronephrosis should be monitored perhaps every 6 weeks with an ultrasound scan and a urological referral made if symptoms develop.

Management
The management of loin pain during pregnancy is mainly conservative in the majority of patients.

Only those who do not respond the medical management will thus require intervention^{16, 17}.

Medical management involves out-patient treatment or a short admission to an observation ward with treatment strategies described above. Patients with known pre-operative diagnoses including PUJ obstruction, ureterocoeles, and urolithiasis can also be thus managed. If there is recurrence of urinary infections with any of these causes, then prophylactic antibiotics should be continued after a therapeutic course.

The need for surgical intervention is determined by the Urological Surgeon, with due consideration of gestational age, anaesthetic risks, and a measured risk of either an immediate undertaking or of delaying the procedure until the patient is delivered. Sometimes, such decisions are not as straight-forward as they might appear.

• Percutaneous nephrostomy with or without antegrade stenting: Recovery is dramatic in patients with sepsis and renal failure. This is usually performed in the intervention suite under local anaesthetic and sedation. The presence of an external tube and a collecting device is usually undesirable, as these may fall out inadvertently. There is <5% complication rate of sepsis and haematuria and a double J stent can be placed at the same time as the nephrostomy, or as a two stage process.
• Double J stents are usually placed in the operating theatre under general or regional anaesthesia with targeted and limited fluoroscopy with lead shielding of the abdomen to minimise exposure to the foetus.
• Ureteroscopy and lithotripsy – either by lithoclast, or electrohydraulic methods and stone extraction is now known to be safe in pregnancy¹⁸. A double J stent is usually placed after this procedure as a safety measure in the event that hydronephrosis of pregnancy is also a contributory factor. This represents a definitive management of stones. Complication rate is <5% and usually includes abrasions, bleeding and infection. Major complication such as major ureteric injuries and avulsion are <1%. Flexible ureterorenoscopy and holmium lasertripsy in pregnancy is not widespread but may well become more utilised in the future.

Conclusion
Flank pain during pregnancy is not an uncommon phenomenon. There may be renal and non-renal causes. Ultrasonography remains the first line of investigation for patients with persistent symptoms necessitating admission. The majority of patients can be managed medically regardless of whether or not a surgical cause has been found. There are absolute indications for a surgical intervention. Ureteroscopic stone extraction is safe, and emerging technologies of flexible ureterorenoscopy and lasertripsy will become more important in future management of these patients as they are less invasive.

References

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14. Lingerman J, Lifshitz D. A, Evan A. P. (2002) Surgical management of urinary lithiasis.Campbell’s Urology, 8th Edition. Philadelphia, PA, Saunders
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