Diagnosis and Staging of Necrotizing Enterocolitis: Current Controversies and a Phenotype-Based Framework

Necrotizing enterocolitis (NEC) remains one of the most devastating gastrointestinal emergencies in neonates and also presents major diagnostic challenges. Despite extensive research, NEC still lacks a practical definition and relies on a set of nonspecific clinical, laboratory, and radiological findings rather than a single pathognomonic presentation or test. The modified Bell staging system remains the most widely used framework in clinical practice and research, but it was originally developed to guide treatment decisions rather than aid diagnosis and has important limitations when applied as a diagnostic aid. Clinical and radiological criteria used for early stages of NEC are nonspecific, disease progression is not always linear, radiographic signs are inconsistently present, and histopathological confirmation is unavailable in most of the cases as surgery is not undertaken in all the cases. These limitations have led to the opinion that even the modified Bell staging is "broken" when it is used to define the disease itself. At the same time, increased understanding about gut immunity and microbiome progression, and neonatal hemodynamics make it increasingly clear that NEC is not a single uniform disease. It is now regarded as a heterogeneous syndrome comprising multiple phenotypes that share a final common pathway of intestinal injury and necrosis differing in timing, predisposing factors, mechanism, and clinical course. These presentations overlap with several neonatal conditions including spontaneous intestinal perforation, septic ileus, cow's milk protein allergy, congenital heart disease-related intestinal hypoperfusion, viral enterocolitis, malrotation with volvulus, and intussusception. This review discusses controversies in the definition and staging of NEC, consolidates alternative diagnostic criteria beyond Bell's system, and elaborates on a phenotype-based framework for clinical distinction. Also, the review sheds light on the clinical mimickers, practical bedside diagnosis using serial clinical assessment and imaging, consequences of NEC, and emerging precision medicine approaches. A shift from stage-based labeling toward a practical, phenotype-informed framework may improve diagnostic precision, reduce misclassification, and enhance both clinical care and research.