Fractal analysis improves tumour size measurement on computed tomography in pancreatic ductal adenocarcinoma: comparison with gross pathology and multi-parametric MRI.

OBJECTIVES: Tumour size measurement is pivotal for staging and stratifying patients with pancreatic ductal adenocarcinoma (PDA). However, computed tomography (CT) frequently underestimates tumour size due to insufficient depiction of the tumour rim. CT-derived fractal dimension (FD) maps might help to visualise perfusion chaos, thus allowing more realistic size measurement. METHODS: In 46 patients with histology-proven PDA, we compared tumour size measurements in routine multiphasic CT scans, CT-derived FD maps, multi-parametric magnetic resonance imaging (mpMRI), and, where available, gross pathology of resected specimens. Gross pathology was available as reference for diameter measurement in a discovery cohort of 10 patients. The remaining 36 patients constituted a separate validation cohort with mpMRI as reference for diameter and volume. RESULTS: Median RECIST diameter of all included tumours was 40 mm (range: 18-82 mm). In the discovery cohort, we found significant (p = 0.03) underestimation of tumour diameter on CT compared with gross pathology (Δdiameter3D = -5.7 mm), while realistic diameter measurements were obtained from FD maps (Δdiameter3D = 0.6 mm) and mpMRI (Δdiameter3D = -0.9 mm), with excellent correlation between the two (R2 = 0.88). In the validation cohort, CT also systematically underestimated tumour size in comparison to mpMRI (Δdiameter3D = -10.6 mm, Δvolume = -10.2 mL), especially in larger tumours. In contrast, FD map measurements agreed excellently with mpMRI (Δdiameter3D = +1.5 mm, Δvolume = -0.6 mL). Quantitative perfusion chaos was significantly (p = 0.001) higher in the tumour rim (FDrim = 4.43) compared to the core (FDcore = 4.37) and remote pancreas (FDpancreas = 4.28). CONCLUSIONS: In PDA, fractal analysis visualises perfusion chaos in the tumour rim and improves size measurement on CT in comparison to gross pathology and mpMRI, thus compensating for size underestimation from routine CT. KEY POINTS: • CT-based measurement of tumour size in pancreatic adenocarcinoma systematically underestimates both tumour diameter (Δdiameter = -10.6 mm) and volume (Δvolume = -10.2 mL), especially in larger tumours. • Fractal analysis provides maps of the fractal dimension (FD), which enable a more reliable and size-independent measurement using gross pathology or multi-parametric MRI as reference standards. • FD quantifies perfusion chaos-the underlying pathophysiological principle-and can separate the more chaotic tumour rim from the tumour core and adjacent non-tumourous pancreas tissue.

Liver surface nodularity: a novel predictor of post-hepatectomy liver failure in patients with colorectal liver metastases following chemotherapy.

OBJECTIVES: The goal of this study was to assess the relationship between liver surface nodularity (LSN), chemotherapy-associated liver injury (CALI), and clinically relevant post-hepatectomy liver failure (CR-PHLF) (i.e., ≥ grade B) in patients undergoing hepatectomy for colorectal liver metastases (CLM). METHODS: Preoperative CT scans of patients who underwent chemotherapy followed by hepatectomy for CLM between 2010 and 2017 were retrospectively analyzed. LSN was measured using semi-automated CT software CT images in patients who had available preoperative CT scans within 6 weeks before hepatectomy, and was computed based on the means of one to 10 measurements by two abdominal radiologists consensually. The association of LSN, CALI, and CR-PHLF was analyzed. RESULTS: Two hundred fifty-six patients were analyzed (149 men and 107 women; overall median age, 61 [range, 29-88 years]). A total of 26 patients (10.2%) developed CR-PHLF. The optimal LSN cut-off value for detecting CR-PHLF was 2.5, as determined by receiver operative characteristic analysis (p < 0.001). LSN ≥ 2.5 was associated with prolonged chemotherapy (> 6 cycles, p = 0.018), but not with CALIs. After propensity score matching, LSN remained significantly associated with CR-PHLF (p = 0.031). Furthermore, multivariate analysis identified LSN ≥ 2.50 and future liver remnant (FLR) < 30% as significant preoperative predictors of CR-PHLF in 102 patients undergoing major hepatectomy. LSN ≥ 2.50 was more frequent in patients undergoing major hepatectomy despite FLR ≥ 30% (p = 0.008). CONCLUSION: LSN quantified on CT is an independent surrogate of CR-PHLF in patients who undergo chemotherapy followed by hepatectomy for CLM and may provide a valuable additional tool in the preoperative assessment of these patients. KEY POINTS: • LSN was not associated with chemotherapy- associated liver injury but high LSN (defined ≥ 2.5) was associated with prolonged chemotherapy (> 6 cycles). • High LSN was an independent predictor of clinically relevant postoperative liver failure in patients undergoing hepatectomy for CRLM. • LSN ≥ 2.50 was more frequent in patients with PHLF after major hepatectomy despite a future liver remnant ≥ 30%.