Cross-sectional imaging of iatrogenic complications after extracorporeal and endourological treatment of urolithiasis

According to the most recent guidelines from the European Association of Urology (EAU), the main indications for active removal of renal calculi include stone growth, obstruction, associated infection, renal insufficiency, and acute and/or chronic pain. Nowadays, open or laparoscopic surgery is reserved for the few patients with complex stone burden after failure of ESWL or endourological procedures, morbid obesity, anatomical abnormalities (such as renal ectopia) not amenable to other therapies and non-functioning kidneys requiring nephrectomy [4].

Currently, there is a consensus that most complex (including partial and complete staghorn) stones should be primarily approached by means of PCNL. ESWL represents the preferred initial approach for pelvic, upper or mid-calyceal calculi up to 2 cm in size as well as for sub-centimetre distal ureteral stones including those at the vesico-ureteral junction. Conversely, due to the limited efficacy of ESWL, endourological procedures such as PCNL and retrograde intrarenal surgery (RIRS) are recommended for large (>2 cm), shockwave-resistant (such as those containing calcium oxalate) or lower pole renal stones. Finally, URS represents the ideal modality for both multiple or single ureteral stones above 1 cm [4].

Since its introduction in the early 1980s, ESWL has dramatically changed the management of urolithiasis and is currently accepted as the preferred and least invasive first-line treatment for the majority (almost 90 %) of patients with renal and ureteral calculi without spontaneous passage. During the last 30 years, its use has become widespread, and millions of treatments have been performed worldwide. Its limited contraindications including pregnancy, coagulation disorders, cardiac arrhythmias, uncontrolled urinary infection, renal failure, anatomic urinary tract abnormalities or obstruction distal to the stone, severe skeletal deformity and obesity, and proximity to an arterial aneurysm [4, 9, 10].

During ESWL, shock waves generated outside the body cross through the soft tissues without loss of strength and cause disintegration of urinary stones into smaller portions through direct shearing force, erosion or cavitation. With the increasing availability of newer and improved lithotripters, the patient tolerance and efficacy of the procedure have increased; therefore, ESWL is usually performed in an outpatient setting without general anaesthesia and can be repeated as necessary. Routine pre-treatment stenting has now been abandoned because it contributes minimally to the prophylaxis of complications and may reduce the stone-free rate (SFR). ESWL achieves a 78–82 % overall success rate (SFR at 3 months) with a significant (45–53 %) proportion of repeated treatments and 8.4–11 % need for auxiliary procedures [4, 9‐14].

Although it may seem a noninvasive modality, ESWL has a reported 15.3 % overall complications rate, which is inferior to that occurring after PCNL and URS. The most common occurrences include cardiac dysrhythmia (11–5 %), bacteriuria (7.7–23 %), bleeding (4–19 %), steinstrasse (3.6–7 %), renal colic (2–4 %) and urosepsis (1–2.7 %) in descending order of frequency, plus sporadic severe cardiovascular events, bowel perforations, liver or spleen haematomas. However, major post-ESWL complications are very uncommon compared to the vast number of procedures performed worldwide and include mostly steinstrasse, severe haemorrhage and urosepsis [4, 13, 14].

Although the mechanism underlying haemorrhage involves the compressive and tensile force of the shock waves on the soft tissues coupled with the cavitation effect on cell integrity, no clear correlation exists with the number and intensity of applied shock waves. Predisposing factors include hypertension, diabetes, obesity, advanced age, coagulation deficits and use of antiplatelet medications. Symptomatic or clinically significant bleeding requiring blood replacement occurs in approximately 2 out of 1,000 treated patients. Similarly, a large multicentre study assessed the incidence of renal haematomas at 0.5 and 0.14 % following ESWL treatment of renal and ureteral stones respectively [4, 9‐11, 13‐16]. Retroperitoneal haemorrhage after ESWL may cause haemodynamic shock and occasionally be fatal [17, 18].

Currently considered the standard procedure for large renal calculi, PCNL is increasingly performed without nephrostomy or ureteral stenting and with the use of ultrasound, pneumatic and Ho:YAG laser devices as well as forceps or nitinol baskets for stone extraction. Contraindications include untreated infections, pregnancy, atypical bowel interposition, and known or suspected kidney tumour. Compared to ESWL, PCNL achieves stone-free status in 95 and 85 % of cases at 1 week and 3 months, respectively, without the need for repeated procedures in the vast majority of cases [4, 19].

Although most patients experience an uneventful postoperative course, percutaneous treatment of urolithiasis is associated with 20–29 % overall and 4–5.2 % severe complication rates, and occasional fatalities. High-risk patients include those with anatomical abnormalities, large or staghorn stones, and comorbidities, such as diabetes, and those requiring upper pole or multisite access. Pre-existent urine infection and absent hydronephrosis represent risk factors for sepsis and severe bleeding, respectively. Following PCNL the most common adverse events include fever (10–23 %) and urinary infection, respiratory impairment (due to pneumothorax, pleural effusion, atelectasis or pneumonia), ileus, bleeding, urosepsis (0.5 % of patients), renal pelvis laceration and ureteral stricture, in descending order of frequency, plus sporadic cases of visceral injuries to the spleen and large bowel. Surgical or interventional treatment is required in up to one-third of all complications [4, 5, 20‐27].

One of the most common and worrisome PCNL-related complications, haemorrhage, occurs in variable entities after nearly one-third of procedures. Perioperative bleeding requiring blood transfusions and/or operative treatment is reported in 3.8–11 % of cases, particularly in patients with comorbidities, advanced age, staghorn calculi and prolonged operative time. After PCNL bleeding may be venous, acute (from injury to the anterior or posterior segmental arteries) or delayed (due to interlobar and lower-pole arterial lesions, arterio-venous fistula or post-traumatic aneurysm) [5, 20, 21, 23, 25, 27, 28].

URS represents an established minimally invasive treatment with a high success rate and acceptable morbidity, which has dramatically improved the outcome of patients with ureteral calculi. Increasingly performed without routine ureteral stenting, URS has recently undergone technical advances including improved equipment, which allows RIRS, intracorporeal lithotripsy using the Ho:YAG laser, and complete stone removal using endoscopic forceps or nitinol baskets. As a result, the expanded indications now range from treatment of small distal ureter stones using a semirigid URS to larger sized renal pelvis stones treated by a flexible URS [4, 29].

Compared to ESWL, URS offers a superior success rate (approximately 90 %) at the expense of greater invasiveness with increased morbidity and longer hospital stays. Reported results include 81.9 %, 87.3 % and 94.9 % SFR for the proximal, mid- and distal ureter respectively, a 7.75 % retreatment rate and need for auxiliary procedures in 18.6 % of cases [14, 30].

The majority of postoperative URS complications are minor occurrences such as haematuria and urinary infection. The risk is further increased by preoperative bacteriuria, hydronephrosis, longer operative time and limited hospital experience. More significant occurrences include persistent haematuria (2 % of cases), renal colic (2.2 %), urosepsis (1.1 %) and bleeding (0.1 %). Furthermore, aggressive ureteroscopic procedures such as RIRS currently represent the leading cause of the reported increase in iatrogenic ureteral injuries. Whereas mucosal damage is relatively common (41–46 % of URS procedures), severe injury involving the muscular layer or deeper may occur in up to 13–18 % of cases and may be largely reduced by prophylactic stenting. Recognition and treatment of ureteral injuries at the time of endourological procedures are strongly related to a better outcome. Ureteral perforation, avulsion or lost segment represent the rarest yet dreaded occurrences [4, 31‐35].

Minimal or moderate degrees of perinephric blood are observed in approximately one-third of patients studied with MDCT shortly after ESWL and PCNL, most usually appearing as dense thickening of the perirenal septa (Fig. 1) [27, 36]. Conversely, clinically significant iatrogenic haematomas appear as hyperattenuating collections (45 to 90 Hounsfield Units, HU) on precontrast scans depending on their more or less acute stage, being relatively hyperdense compared to the renal parenchyma (Figs. 3, 4, 5 and 6). In our experience, iatrogenic haematomas are most commonly or initially subcapsular with the characteristic crescent- or biconvex-shaped appearance limited by the renal capsule, causing compression on the adjacent parenchyma, indenting or flattening the renal margin. Haemorrhage extends variably into the retroperitoneum, mostly by occupying the peri- and pararenal spaces. Primarily perinephric haematomas are demarcated by the Gerota’s fascia and cause renal displacement. Furthermore, focal parenchymal injuries closely similar to traumatic lacerations may be observed as non-enhancing linear or irregular clefts (Figs. 3, 4 and 7). Heralded by linear or flame-shaped high attenuation (85—370 HU) structures corresponding to CM extravasation, active bleeding at MDCT indicates probable failure or nonsurgical management and represents the strongest indication for interventional or surgical treatment. Furthermore, MDCT provides consistent follow-up of conservatively treated lesions showing progressive demarcation, size reduction and decreasing attenuation of haematomas (Figs. 3, 4 and 6) [16, 39].

The majority of iatrogenic renal haematomas tend to reabsorb and can be successfully managed conservatively, including appropriate transfusion support when signs of hypovolemic shock or haemoglobin decrease are present. Conversely, angiographic embolisation or surgical exploration are reserved for haematomas with MDCT evidence of ongoing arterial bleeding and for those cases that do not respond to a “watchful waiting” strategy. Required in less than 1 % of patients, superselective embolisation is the treatment of choice and extremely effective in stopping haemorrhage, with 100 % technical and 95 % clinical success rates [5, 16, 28, 44, 45].

Most haematomas resolve within 2 years without adverse effects on blood pressure and renal function. Persisting liquefied haematomas may be amenable to percutaneous drainage. Alternatively, the “Page kidney” phenomenon consisting of long-term development of hypertension from renal compression, ischaemia and hypoperfusion causing activation of the renin-angiotensin-aldosterone system has been reported [9, 46].

Furthermore, after PCNL, bleeding may occasionally manifest as suburothelial haemorrhage (SH) of the renal pelvis and ureter (Fig. 7). A very rare although well-established condition, spontaneous SH most usually occurs secondary to an excessive warfarin anticoagulant therapy condition, sometimes with haemophilia or other coagulation disorders. The characteristic CT appearance includes a circumferential hyperattenuating mural thickening of the renal pelvis, sometimes extending along the proximal ureter, with an increased density that is often subtle and better appreciable on unenhanced scans with narrow window settings. On nephrographic images, the mural thickening is less conspicuous and appears as soft-tissue thickening, hypodense compared to opacified urine in the collecting system. Despite encasement of the renal infundibulum, luminal compression and upstream calyceal dilatation are absent or minimal. In the excretory phase small nodular filling defects or predominantly smooth narrowing of the renal pelvis and ureter are noted, so that misinterpretation as pyeloureteritis cystica, pyonephrosis or transitional cell carcinoma may occur. The usual fate is rapid, complete resolution of imaging changes following conservative treatment [47‐49].

Cross-sectional imaging signs of urinary infection are mostly conspicuous in the nephrographic phase MDCT acquisition. Infectious pyeloureteritis is heralded by pelvicalyceal and/or ureteral thickening with prominent urothelial enhancement (Figs. 2, 8 and 9). Because of inflammatory debris obstructing the renal tubules and impaired function from tubular ischaemia, acute pyelonephritis appears as a more or less enlarged, oedematous kidney with decreased parenchymal enhancement (Fig. 8) or with the characteristic “striated nephrogram” appearance including well-defined wedge-shaped areas, linear bands or streaky zones of reduced enhancement perpendicular to the cortical surface. Accessory signs such as perinephric fat stranding and thickening of Gerota’s fascia are commonly observed (Fig. 8). Progression of infection may lead to the formation of variable-sized intra- or perirenal abscesses (Fig. 9) with a characteristic appearance of round or geographic hypoattenuating collections, usually surrounded by a peripheral thickened enhancing capsule and by decreased parenchymal enhancement corresponding to non-necrotic infected kidney [50, 51].

Defined by an infected hydronephrosis, pyonephrosis represents a urological emergency that requires prompt intervention to prevent sepsis and development of impaired renal function. Radiologists should maintain a high level of suspicion, since imaging differentiation of pyonephrosis from hydronephrosis is challenging. Useful signs of an infected collecting system include renal enlargement with a striated or poorly functioning nephrogram, perinephric fat inflammatory changes and urothelial thickening (Fig. 8). Occasionally the obstructed cavities show higher-than-water (10–50 HU) attenuation and/or fluid-fluid levels corresponding to purulent urine. Decompression by means of nephrostomy or ureteral stenting relieves obstruction and allows confirming the diagnosis [50, 51].

Major ureteral injuries with full-thickness mural involvement are increasingly reported after ureteroscopic stone removal (including RIRS) and occasionally PCNL, and involve the proximal, middle and distal ureter in 51 %, 14 % and 35 % of cases, respectively. Resulting from disruption of the urinary tract, iatrogenic urinomas represent abnormal collections of extravasated urine, which may collect close to the site of the renal pelvis or ureteral injury and otherwise variably dissect into the retroperitoneum. Often clinically unsuspected but associated with significant morbidity from superinfection, iatrogenic urinomas are mostly treated by prolonged nephrostomy or ureteral stenting [35, 37, 38].

Whereas in the past ureteral lacerations and urinomas were usually depicted by means of trans-nephrostomy or ascending pyelography, nowadays the diagnosis is usually made by MDCT. Urinomas commonly appear as confined collections measuring 0–20 HU in unenhanced scans and may be misinterpreted as ascites, abdominal or pelvic abscesses, cystic masses or chronic liquefied haematomas. The imaging hallmark of the urinoma is represented by opacification (up to 80–200 HU) corresponding to an enhanced urine leak observed on excretory-phase or MDCT urography acquisitions. Opacification is usually inhomogeneous in larger lesions and usually progresses over repeated delayed-phase acquisitions [37‐40].

Resulting from previous minor (mucosal) injuries to the urinary tract, late strictures predominantly occur at the distal third of the ureter and are typically depicted by MDCT or MR urography as a tight stricture with upstream hydronephrosis (Fig. 10) or are benign-type smooth tapering without an associated soft-tissue mass (Fig. 11). Since retrograde stenting is frequently unsuccessful, most ureteral injuries are treated by means of nephrostomy with or without a ureteral catheter. Whereas endourological repair of small ureteral fistulae and strictures may be performed in selected cases, most delayed occurrences need deferred reconstructive surgery such as uretero-ureterostomy or uretero-neocystostomy to preserve renal function [5, 33‐35].