Incidental extravascular findings in CT angiograms in patients post endovascular abdominal aortic aneurysm repair: clinical relevance and frequency

Endovascular aneurysm repair (EVAR) has become the predominant treatment option for patients with abdominal aortic aneurysm (AAA) accounting for 78% of all elective repair in the United States in 2010 (Dua et al. 2014). In addition, recent large multi-centre randomised trials have demonstrated similar short-term outcomes between EVAR and open surgical repair for the treatment of ruptured AAA which may further increase endovascular management (Trial et al. 2009; Hoornweg et al. 2007).

Despite superior perioperative mortality outcomes and similar long-term survival compared to open surgical repair (Lederle et al. 2009; Greenhalgh et al. 2004), EVAR is beset by its higher rates of observed complications and need for secondary intervention (De Bruin et al. 2010; Hobo et al. 2006). Indications for re-intervention often include stent migration and endoleak with the associated risk of subsequent aneurysm rupture. Life-long surveillance is therefore recommended by multiple societies (Walker et al. 2010). Computed tomography angiography (CTA) remains the most widely used imaging modality for the purposes of pre-operative planning and surveillance due to its availability, high-throughput, reproducibility, contrast resolution and volumetric multi-planar reconstruction functionality. Although there is no consensus on surveillance frequency and modality, commonly used protocols traditionally incorporated arterial phase CTA imaging at 1, 6 and 12 month periods post-procedure and subsequent yearly follow-up (Hirsch et al. 2006). Several studies have demonstrated this can be done with similar sensitivity and specificity for endoleak detection as multiphase CT (Iezzi et al. 2006; Macari et al. 2006). Furthermore, some authors advocate the sole use of annual Doppler ultrasound for endoleak detection if no complications have been demonstrated on CTA at 12 months post-procedure (Chaer et al. 2009; Sternbergh 3rd et al. 2008).

Incidental findings are commonplace in clinical radiology and whilst they may lead to early significant diagnoses, over-diagnosis with unnecessary procedural or imaging work up and psychological distress to patients can also occur. Extravascular structures are readily depicted on CTA and previous studies demonstrated the prevalence of clinically significant incidental findings to be in the range of 5.6 and 12% (Katz et al. 1999; McDougal et al. 2006). Interestingly, higher rates of detection were shown in more recent studies which focussed on lower limb run off CTA with figures as high as 27% in patients presenting with acute limb ischaemia (Preuss et al. 2015). Therefore, our objectives were to primarily evaluate the frequency and clinical relevance of extravascular incidental findings (EVIF) in the post EVAR patient sub-set who undergo CTA and secondarily to assess reporting accuracy by retrospectively scrutinising prior images for evidence of early disease in cases where malignant findings had been demonstrated.

In our study, a total of 950 EVIFs were noted in 2203 CT scans of 418 patients (31 females (7.4%), 387 males (92.6%); age range 63–93, mean age 79.0 ± 6.6(SD) years; mean scans per patient 5.3 ± 2.8(SD)). There were 115 patients (27.5%) with 144 Class I findings, 165 patients (39.5%) with 209 Class II findings and 304 patients (72.7%) with 597 Class III findings. At least one finding was noted in 362 patients (86.6%) and 38 patients (9.1%) had findings in all three categories.

There was a spread of 12 different malignancies identified. The highest overall frequencies of incidental malignancies were colorectal cancer (10), urinary bladder cancer (9) and lung cancer (8). The distribution of colorectal cancers included four caecal and two each in the ascending colon, sigmoid and rectum. Amongst the 27 malignant findings identified on the planning CTA, the most frequent were colorectal (7) and urinary bladder (6) cancers. Urinary bladder cancer (3) and liver metastasis (3) were the most common missed malignant findings in retrospect. The others included pancreatic cancer (1), renal cancer (1), lung cancer (1), colorectal cancer (1), prostate cancer (1), bone metastasis (1) and Non-Hodgkin’s Lymphoma (1). Three lung and two colorectal cancer cases were the most frequent malignancies that could not be identified on previous scans even in retrospect. Figure 1 includes examples of subtle missed early malignant findings.

A high number of significant EVIFs can be identified in follow-up CTAs of patients who undergo EVAR, which is of importance in this higher risk cohort of elderly patients with multiple co-morbidities. Many of these EVIFs were followed up and were shown to cause a change in the management of patients by aiding early diagnoses.

This study included a large sample of patients (418) and scans (2203) compared to previous studies, ranging from 82 to 290 patients (Preuss et al. 2015; Tornqvist et al. 2016; Naidu et al. 2010; Indes et al. 2008; Waqas et al. 2014; Gufler et al. 2014). The incidence of EVIFs in Class I was higher than most previous studies (range 6.5% – 23.7%), but lower than 37 and 42% in Tornqvist et al. and Indes et al.’s studies respectively (Katz et al. 1999; McDougal et al. 2006; Preuss et al. 2015; Tornqvist et al. 2016; Naidu et al. 2010; Indes et al. 2008; Waqas et al. 2014; Gufler et al. 2014). In our study, classification of EVIFs was similar to Preuss et al.’s study, which explains the comparable 27% of EVIF incidence (Preuss et al. 2015). However, the lack of standardisation of EVIF definitions and differences in EVIF classification across other studies make the results less directly comparable. Difference in the scanner type (single helical CT) and inclusion of the venous phase in Katz et al.’s and Naidu et al.’s studies respectively, may have also influenced the findings (Katz et al. 1999; Naidu et al. 2010).

The marked gender imbalance (92.6% males) in the study could possibly explain the few gynaecological pathologies detected while the lack of EVIFs in the MSK region compared with other studies could be accounted for by the total area imaged that included lower limbs in other publications (Preuss et al. 2015; Naidu et al. 2010). Overall findings of high frequencies of pneumonia, gallstones, simple renal and hepatic cysts, diverticular disease and degenerative lumbar spine in each class were in line with previously reported studies (Preuss et al. 2015; Waqas et al. 2014; Iezzi et al. 2007). However, our follow-up rate (80%) for important EVIFs was significantly better than other studies (40% reported in Preuss et al., 58% in Naidu et al. and 73% in McDougal et al.) (McDougal et al. 2006; Preuss et al. 2015; Naidu et al. 2010).

Most lung consolidative changes were identified on the first post-EVAR CTA and were likely due to secondary complications of hospital admissions. Patients who were asymptomatic at the clinical follow up required no intervention. A large number of patients who underwent further work up for suspicious lesions yielded malignant results (51 of 85). This highlights the importance of a low threshold for further investigation of patients who had Class I EVIFs diagnosed on surveillance CTAs.

In our study, there was a higher incidence of incidental malignancies (12.2%) compared to previous studies (range 0–5.2%) (Preuss et al. 2015; Tornqvist et al. 2016; Naidu et al. 2010; Gufler et al. 2014; Iezzi et al. 2007; Belgrano et al. 2010; Prabhakar et al. 2015; Hughes et al. 2016; Ho et al. 2016). This could be attributed to the nature of our study, which included surveillance CTAs over an extended period and larger number of scans. It can be postulated that the greater malignant findings detected was more likely in an elderly age group with higher co-morbidities, although similar patient demographics were observed in Preuss et al., Tornqvist et al., Gufler et al., and Indes et al.’s studies (mean age 74.9, 78.7, 81.6, and 76 respectively) (Preuss et al. 2015; Tornqvist et al. 2016; Indes et al. 2008; Gufler et al. 2014). Certain malignancies were also known to clinicians at diagnosis (10 of 51) but not included in the request reports and were unknown to the reporting radiologists. However, this was still relevant and included as it remained a new diagnosis to the radiologist.

The high frequency of urinary bladder cancer in the cohort was an intriguing observation while the high number of colorectal cancers was unsurprising.

A possible explanation for the commonly missed liver malignancy could be the limitation of an arterial phase scan in detecting and characterising liver lesions. Some missed early malignant findings were also very subtle in retrospect and could be easily overlooked or dismissed as a benign finding at the time of reporting. However, it is difficult to draw conclusions due to the small number of cases. All retrospectively missed incidental malignant findings were discussed at the departmental discrepancy meeting and any unexpected findings were escalated in accordance with the Royal College of Radiologists (RCR) and General Medical Council (GMC) Duty of Candour statements (The professional duty of candour 2015).

A limitation of our study included a possible underestimation of EVIFs as only the final scan reports were reviewed. However, as the surveillance scans were reported by experienced consultant radiologists and any previous scans were compared during reporting, the number of undetected EVIFs should be limited in number. Follow up data did not include paper medical records, which accounted for the incomplete clinical follow up rates. A few patients had also died prior to a full work up or follow up. While an interesting aspect of our study included the retrospective review of incidental malignancies on surveillance CTA, our results may have been biased by the reviewing radiologists having prior knowledge of the clinical diagnosis.

A significant amount of EVIFs, particularly incidental malignancies, can be detected in surveillance CTAs of patients post-EVAR. Hence, it is prudent to be vigilant in evaluation of abdominal CTAs and necessary clinical follow-up arranged. Comprehensive overview of checklist areas with particular attention to the liver and bladder, which were commonly missed sites for early pathology, can be suggested on the basis of our findings. It remains to be seen if change in patients’ management following important EVIF detection and arguably earlier diagnoses, significantly translates into improved patient outcome. Future work may include the cost analysis and radiation exposure of follow up imaging and potential procedures.