This study has an ethical approval by the Helsinki University Hospital (Helsinki, Finland) ethics committee. All experiments were performed in accordance with relevant guidelines and regulations. An informed consent was obtained from all patients and/or their legal guardian(s).
Patients and study design
All patients treated in the Children’s Hospital, Helsinki University Hospital for pediatric IF were reviewed, and SBS patients born between years 1988 to 2018 were identified. SBS was defined as PN requirement for over 60 consecutive days and/or surgical removal > 50% of age adjusted small intestine11. All patients had undergone a bowel resection and non-operatively treated NEC patients were not included in the study. Overall, 78 SBS patients were identified, of whom 77 with available follow-up data were included (Table 1). Of them, 62 patients had a liver biopsy obtained. Patients with NEC as the underlying etiology (NEC-SBS n = 38) were compared to those with other causes of SBS (non-NEC-SBS n = 39). The other causes of SBS included midgut volvulus (n = 13), small bowel atresia (n = 9), extended Hirschsprung’s disease (n = 8), gastroschisis with atresia (n = 6) and isolated gastroschisis (n = 3).
Data were prospectively collected from 2010 onwards and retrospectively before 2010 (last follow up date was before year 2010 in 4 patients). Since 2009, a standardized multidisciplinary management and follow-up program including modern fish oil containing lipid emulsions, antimicrobial catheter locks, autologous reconstructive (AIR) surgery (serial transverse enteroplasty, STEP, and longitudinal intestinal lengthening and tailoring, LILT), and intestinal transplantation has been running in our center11,12. As described in detail previously, liver biopsies are routinely used to assess IFALD within our IF rehabilitation program5.
Clinical data, including gestational age and weight, anatomy of the remaining bowel, surgical procedures and PN duration (from start to weaning off) were collected from the patient records. Number of blood culture positive septic episodes was recorded from birth to follow-up. Percentage age-adjusted small bowel and colon length was calculated based on published age-specific normal values13,14. Follow-up continued until the end of 2020 allowing for at least two years follow up for each patient after end of study inclusion period in 2018. The follow up data was collected at the latest follow up visit (n = 70) or at last follow up before intestinal transplantation (n = 2) or death (n = 5).
Blood samples were drawn after overnight fast. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma glutamyl transferase (GGT), total and conjugated bilirubin, platelet count, and bile acids were analyzed using standard hospital laboratory methods. The APRI index was calculated [(AST/upper limit of normal) × 100 /platelet count (109/L)]15. Serum citrulline, a marker of bowel enterocyte mass, was measured by using an automatic amino acid analyzer (Biochromon 30 Physiological and Midas Autosampler, Biochromon Limited, Cambridge, England) as described earlier16.
Liver biopsies and histopathology
Core needle liver biopsies were taken under general anesthesia with ultrasound guidance for diagnosis or follow-up during surveillance intestinal endoscopies or planned laparotomies5,17. As described previously, follow-up liver biopsies were obtained when previous biopsy showed abnormal and potentially progressive histopathology5. Liver biopsies were analyzed by two experienced pediatric liver pathologists to consensus according to a standardized histopathological protocol5,17. As liver biopsies contained median 15 (5–22) portal areas they were considered representative. The biopsies were scored for cholestasis (grade 0 to 3; absent, minimal, marked, prominent), portal inflammation (grade 0 to 4; absent, minimal, mild, moderate, prominent), steatosis (grade 0 to 3; < 25%, 25–50%, > 50% of hepatocytes affected) and fibrosis (Metavir stage from 0 to 4) as previously described5. IFALD was defined as any abnormal finding in liver biopsy, including cholestasis, portal inflammation, fibrosis or steatosis. Active IFALD was defined as presence of histological cholestasis and/or portal inflammation and chronic IFALD as presence of Metavir fibrosis stage ≥ 2 and/or steatosis grade ≥ 2 without cholestasis or inflammation5.
IBM SPSS statistics, version 25 was used for data analysis. All results are presented as medians with interquartile range (IQR), unless stated otherwise. Mann–Whitney U-test and Fisher’s exact test was used to compare statistical significances between the two groups. Kaplan–Meier log rank survival analysis was used to evaluate cumulative occurrence of IFALD and weaning off PN. Predictive factors for weaning off PN and the presence of histopathological IFALD were analyzed with univariate and multivariate Cox regression analyses. Statistical significance is defined as p-value < 0.05.