When a ureter is suddenly blocked while the kidney continues to filter, pressure in the collecting system rises. The classical work on pyelovenous backflow showed that fluid then leaves the system through the fornices of the calyces, where the wall is thinnest, and tracks into the renal sinus, veins and lymphatics (Hinman and Lee-Brown, 1924). Forniceal rupture is this process made visible: a small tear that decompresses the kidney and usually seals when the obstruction is relieved. In the series analysed by Gershman et al. (2011) ureteric stones were by far the commonest cause, and the responsible stones were typically small and lodged in the distal ureter.

Rupture of the renal pelvis is a different lesion, a breach in the wall of the pelvis itself. It is much less common, tends to produce a larger and more persistent leak, and has been associated with pre-existing weakness of the wall from infection, previous surgery or long-standing obstruction. The two are often reported under the same heading of spontaneous urinary extravasation, which makes the literature hard to interpret. In this article the word spontaneous means that no trauma or instrumentation preceded the leak, and the pathway asks the clinician to record which of the two lesions is present whenever imaging allows.

The largest series of fornix rupture found that most patients were managed successfully and that serious complications were uncommon (Doehn et al., 2010). A later report asked directly whether conservative treatment was safe and concluded that, in selected patients without infection, it was (Morgan et al., 2017). At the other end of the range of practice, primary ureteroscopy with removal of the stone has been described as initial treatment (Kalafatis et al., 2004). These reports are retrospective and concern mainly forniceal leaks. For true pelvic rupture the evidence is limited to isolated cases, and the proposals below lean on first principles and on guidance written for obstruction in general.

No symptom is specific. Extravasation is usually found in someone being assessed for ordinary renal colic. Features that should raise suspicion are pain that changes character, from colicky to constant or from severe to suddenly eased, flank tenderness with guarding that is out of proportion to simple colic, and fever. Because a sudden fall in pressure can relieve pain, improvement does not exclude a leak. The first step is therefore an attitude: to keep the diagnosis in mind when the clinical picture and the size of the stone do not match.

Non-contrast computed tomography is the standard first test for suspected ureteric stone (Smith et al., 1995; Coursey et al., 2012), and ultrasonography is an accepted initial alternative (Smith-Bindman et al., 2014). Neither demonstrates a leak directly. Non-contrast images show perinephric stranding and fluid, which are common in obstruction without rupture. The pathway therefore proposes that, when a fluid collection is seen around the kidney or along the ureter and renal function permits, contrast-enhanced computed tomography with a delayed excretory phase be obtained. Opacified urine outside the collecting system confirms extravasation, and the site and volume of the leak help to separate a forniceal tear from a breach of the pelvis. Where contrast cannot be given, the diagnosis rests on the size and behaviour of the collection on repeat imaging.

Management should follow from risk, not from the radiological label alone. Table 1 lists the features the pathway asks the clinician to assess and the response proposed for each. Infection carries the most weight. An obstructed kidney with signs of infection is a urological emergency under existing guidelines whether or not urine has leaked (Türk et al., 2016a), and sepsis should be recognised with the criteria of the international consensus definitions (Singer et al., 2016). Infected urine in the retroperitoneum adds the risk of abscess.

For a small forniceal leak in someone who is afebrile, with a stone likely to pass, good renal function and two kidneys, the pathway proposes observation: analgesia, with non-steroidal anti-inflammatory drugs as the first choice where they are not contraindicated (Holdgate and Pollock, 2004), clinical review, and a low threshold for repeat imaging. Whether prophylactic antibiotics are needed in the absence of infection is unknown, and the pathway leaves the decision to local policy. Medical expulsive therapy may be considered on the same terms as for any ureteric stone (Hollingsworth et al., 2006).

In all other cases, the pathway proposes decompression. In obstruction with infection, a retrograde ureteric stent and a percutaneous nephrostomy were found to be equally effective in a randomised comparison (Pearle et al., 1998), and observational data link decompression to lower mortality in sepsis with ureteric stones (Borofsky et al., 2013). The choice can be made on availability and on the condition of the patient. A stent has the advantage of splinting the collecting system and lowering pressure across a pelvic tear. A nephrostomy avoids instrumenting a ureter under pressure and allows antegrade study later. A large or infected urinoma may need a separate percutaneous drain. Management of sepsis itself follows established principles of early antibiotics, resuscitation and source control (Wagenlehner et al., 2013).

Definitive treatment of the stone follows the usual indications and techniques (Türk et al., 2016b). The question specific to this setting is timing. In the presence of infection, guidelines advise that stone removal be deferred until the infection has been treated. Where there is no infection, primary ureteroscopy has been reported (Kalafatis et al., 2004), but pressurised irrigation in a system that has already leaked could in principle enlarge the extravasation. The pathway therefore proposes that definitive treatment normally be delayed until the leak has had time to seal, and that primary ureteroscopy be reserved for small forniceal leaks treated with low irrigation pressure by an experienced operator.

The final step is to show that the leak has closed, that any collection has resolved and that the kidney drains. For a small forniceal tear with an uneventful course, clinical recovery and a follow-up ultrasound scan may be enough. After pelvic rupture, or where a drain or nephrostomy was placed, the pathway proposes contrast imaging before tubes are removed. Complications should be recorded in a standard form, for which the classification of Dindo et al. (2004) is suitable, so that experience can be pooled between units.