Insights into the pathophysiology and classification of type 4 choledochal malformation.

Introduction: Type 4 choledochal malformations (CMs) can be defined as extra- and intrahepatic biliary dilatation. They are of uncertain etiology but make up about 20% of most series. The aim of this study was to investigate the pathophysiology and their natural history following surgical intervention.

Methods: Ambispective review of a single-center series of type 4 CM between 1996 and 2017. Perioperative imaging, intraoperative pressure monitoring, bile amylase, and long-term follow-up data were analyzed based on extrahepatic morphology [(cystic (C), fusiform (F)]. Data were expressed as median (range). Statistical analysis was performed with nonparametric tests. P < 0.05 was considered significant.

Results: 37 children had type 4 CM in the study period [age at surgery 4 (0.2-16) years] and could be further subdivided into cystic (4C) (n = 22) or fusiform (4F) (n = 15). There was significantly greater dilatation of the extrahepatic component in the cystic group [30 (11-94) versus 15 (8-90) mm; P = 0.0002] though there was no difference in left duct diameter [cystic 7.5 (0-17) mm versus fusiform 7.5 (3-16) mm; P = 0.86]. There was a trend to higher choledochal pressure in the cystic group [19 (4-40) versus 9 (6-25) mmHg; P = 0.09] and those in the fusiform group had higher bile amylase [8650 (3-890,000) versus 592 (1-123,000) IU/L; P = 0.01] and were older [4.1 (0.92-16.43) versus 2.4 (0.15-15.48) years; P = 0.03]. Children with type 4 CM were then separated simply on the basis of bile amylase into LOW (characterized by high pressure, cystic morphology and young age at surgery) and HIGH bile amylase (low pressure, fusiform morphology and older at time of surgery).

Conclusions: We propose further division of type 4 CM into 4C and 4F on clinical and pathophysiological grounds.

Level Of Evidence: II (prospective cohort).