Multidetector CT imaging of complications after laparoscopic nephron-sparing surgery

The RENAL (Radius, Exophytic, Nearness, Anterior, Location) nephrometry score (Table 1) was recently introduced as a reproducible means to describe the relevant tumour anatomy, stratify the complexity of renal masses, and objectively compare perioperative and long-term outcomes. The RENAL score includes the five most reproducible features—namely, diameter, exophytic or endophytic growth, proximity to the collecting system, anterior versus posterior location and relationship to the polar lines, which should be assessed on volumetric contrast-enhanced multidetector CT including renal vascular, parenchymal and excretory imaging (Fig. 1) [26, 27]. Tumour staging and complexity dictate the urologist’s therapeutic choice: increasing RENAL scores were found to be strongly associated with RN and O-PN rather than L-NSS [28].

In the majority of patients, L-NSS is performed via the transperitoneal (TP) route; conversely, posterior and postero-lateral renal tumours are best managed with a retroperitoneal approach [9, 11, 29, 30]. Preoperative ureteral catheterisation may be used, particularly when access to the collecting system is necessary. According to some authors, intraoperative ultrasonography for assessment of renal perfusion, tumour location and borders may prove beneficial and result in a change of procedure in a minority (2.5 %) of patients [31]. After laparoscopic access to the retroperitoneum and opening of Gerota’s fascia, en bloc or selective arterial clamping of the renal hilar vascular pedicle is performed to decrease bleeding and ensure a clear surgical field: the acceptable warm ischaemia time is limited to 30 min or less. Depending on the tumour’s size and location, NSS options include segmental polar nephrectomy, wedge resection, transverse resection and enucleation, to obtain complete tumour excision with a proper margin of normal tissue, and preservation of the maximum possible amount of functioning renal parenchyma. After removal of the resected renal portion, surgery requires suture repair of collecting system defects, filling of the parenchymal defect with peri-renal fat or bioabsorbable bolster agents, renal parenchymal reconstruction and closure with a combination of absorbable sutures, argon-beam coagulation and haemostatic agents. Finally, after reconstruction is finished, the vascular clamp is released to restore circulation. Hilar masses, multiple and/or infiltrating tumours with pelvicalyceal involvement pose specific and significant technical challenges for NSS. In selected patients, conversion to laparoscopic RN or O-PN may be necessary when L-NSS is deemed unfeasible by the surgeon after renal exploration [9, 11, 29, 30].

Resulting from inadequate suturing or coagulation of transacted blood vessels, early postoperative haemorrhage with or without radiologically identifiable active bleeding represents the most common complication after L-NSS, with a reported incidence approaching 6–8 % of procedures. Blood transfusions are required in 5–21 % of patients and constitute a Clavien grade II complication [6‐12].

As mentioned above, minimal or moderate degrees of peri- and para-renal blood are generally apparent after L-PN and should not be reported as abnormal. However, intra-luminal blood is closely related to gross haematuria and is identified on unenhanced CT scans as hyperattenuating content of the pelvicalyceal system (Fig. 3). In our experience, clinically significant iatrogenic haematomas after L-NSS appear as hyperattenuating collections compared to the renal parenchyma, which measure between 45 and 90 Hounsfield units (HU) depending on their stage, and mostly occupy the peri- and para-renal spaces (Figs. 4, 5, 6). Indicated by strongly hyperattenuating (85–370 HU, isodense to enhanced arterial vessels) foci corresponding to CM extravasation in the vicinity of the SSR, active bleeding at CT (Fig. 6) indicates a high risk of failure of conservative management and thus represents the strongest indication for interventional or surgical treatment. In addition, multidetector CT provides consistent follow-up of conservatively treated lesions (Figs. 5, 6) showing progressive demarcation, size reduction and decreasing attenuation of haematomas [22‐25, 44, 52].

According to the EAU guidelines, iatrogenic renal vascular injuries (IRVI) rank among the rarest (less than 1 % overall), yet most feared complications after percutaneous biopsy, nephrostomy, nephroureterolithotomy, renal artery angioplasty or stenting, and NSS. The IRVI spectrum encompasses arterio-venous fistulas (AVFs), renal pseudoaneurysms (R-PA), vascular thrombosis and renal infarction. IRVIs can lead to significant morbidity, including massive haemorrhage, life-threatening haematuria, need for nephrectomy or deterioration of renal function [24, 32, 37].

Renal artery and intra-parenchymal pseudoaneurysms occur after 0.43–1.3 % of L-NSS procedures, and result from partial or complete injury to an intra-renal artery at the SSR, the main renal artery or one of its main branches. Specifically, R-PA may form when the combined effect of hypotension, coagulation and pressure from the adjacent structures leads to temporary cessation of the bleeding, followed by recanalisation from clot degradation. R-PAs may sometimes grow, become unstable from restorated blood flow, and eventually erode into the pelvicalyceal system or the surrounding perinephric tissues. Most cases are diagnosed during the first 2–3 weeks after surgery, occasionally after a few months’ delay. Diagnosing R-PA requires a high level of suspicion, since clinical manifestations are often vague or non-specific such as flank pain, gross haematuria, dizziness and fever [11, 32, 53, 54].

Ultrasound may detect R-PA as a cystic mass or liquefied haematoma, with the characteristic “to-and-fro” internal flow at colour-Doppler sonography. On unenhanced CT images, a haematoma is commonly seen near to the surgical site, often associated with hyperattenuating blood clots in the renal pelvis, but the pseudoaneurysm itself is usually not visible. Conversely, arterial-phase CT-angiography acquisition shows a roundish, well-circumscribed lesion (usually measuring 1–3 cm) with contained arterial phase enhancement that appears isodense to the adjacent arterial vessels and becomes isoattenuating relative to the blood pool during the nephrographic phases (Fig. 7). Coronal CT-angiographic maximum intensity projection (MIP) reconstructions allow visualisation of the R-PA with its relationship to the renal vasculature. A R-PA may be missed in the excretory phase, owing to CM wash-out from the cavity [22‐25, 44, 53, 55].

AVFs are most commonly iatrogenic rather than congenital; they are indicated by macro- or micro-haematuria from rupture within the collecting system, and may cause variable degrees of blood loss. The CT hallmark of AVF includes tortuous arteries and early or simultaneous opacification of one or more intra-parenchymal arteries and veins during the corticomedullary phase (Fig. 8) [55, 56].

Occasionally, arterial clamping may injure the vessel intima, thus leading to thrombosis, infarction and atrophy. CT-angiography depicts arterial thrombosis as abrupt vessel cut-off, and renal infarction (Fig. 8) as a peripheral wedge-shaped non-enhancing area in the renal parenchyma, with a rim of enhancement at the periphery of the cortex (rim sign) due to preserved capsular blood flow [22, 24].

Selective angiography evaluates the lesion dynamically and allows planning for trans-arterial embolisation (TAE) and super-selective catheterisation [56]

In the past, severe bleeding and IRVIs required laparotomy. Currently, the therapeutic approach is increasingly conservative, provided that clinical and laboratory parameters remain stable and CT excludes active bleeding. Although haematomas and IRVI may heal spontaneously with conservative management, selective TAE (Figs. 7, 8, 9) is recommended as the established minimally invasive treatment of choice for life-threatening occurrences with persisting or massive bleeding, severe haematuria from communication to the pelvicalyceal system, or progressively deteriorating renal function. Notably, the need for interventional treatment such as TAE constitutes a major (Clavien grade III) complication. Arteriography confirms R-PA as an ovoid CM pool close to the SSR (Fig. 7). In patients with post-surgical IRVI, TAE using coils or other embolisation agents proved to be safe and effective treatment with a low rate of complications, rapid recovery and short hospital stay, and excellent (nearly 100 %) technical and clinical success rates, respectively corresponding to complete angiographic exclusion of bleeding and haemodynamic stabilisation without the need for blood transfusion. Super-selective embolisation, carried out as distally as possible is recommended to minimise parenchymal loss and avoid long-term impairment of renal function [32, 55, 56].

Occasionally, fluid collections (seroma, haematoma or urinoma) forming close to the SSR after L-PN may become infected. Differentiation of non-infected collections from an abscess requires correlation of clinical signs and laboratory data with imaging appearances, mostly represented by enlarging intra- or peri-renal hypoattenuating collections with a peripheral, thickened enhancing capsule (Fig. 10). Alternatively, the residual renal parenchyma may show the characteristic “striated nephrogram” appearance consistent with pyelonephritis [22‐25, 57, 58].

Surgical access to the collecting system is necessary to ensure an adequate margin of resection for tumours extending deeply into the renal parenchyma: if the subsequent pelvicalyceal repair is not watertight, urine may leak into the surgical bed leading to a peri-renal urinoma or collection of a mixture of blood and urine. Urine leakage has been estimated to occur in 1.3-3.6 % of L-PN interventions [6‐12].

The characteristic appearance of leakage seen on CT relies on identification of CM-opacified urine (80–200 HU) extravasated from the collecting system into the peri-renal space, visualised on excretory phase acquisitions (Fig. 11). Urinomas appear as more or less homogeneous collections, with progressive opacification over repeated delayed acquisitions [22‐25, 49, 52].

Most urine leaks resolve spontaneously over time and are generally managed conservatively with ureteral stenting, Foley catheter or percutaneous nephrostomy. Endourological fulguration and percutaneous imaging-guided drainage may be required to treat persistent leaks and urinomas, respectively [29, 49].