Paediatric Radiology · Neonatal abdominal imaging · Walsh–Kliegman modification

Modified Bell staging of necrotising enterocolitis

Clinical–radiological staging of neonatal necrotising enterocolitis from suspected disease to advanced disease with intestinal perforation.

Purpose

To grade the severity of necrotising enterocolitis using systemic, intestinal and radiographic findings and to support consistent communication and management decisions.

Stage	Designation	Systemic signs	Intestinal signs	Radiographic signs
IA	Suspected NEC	Temperature instability, apnoea, bradycardia or lethargy	Increased gastric residuals, mild abdominal distension or occult blood in stool	Normal appearance, mild intestinal dilatation or mild ileus
IB	Suspected NEC	Same as IA	IA findings with gross rectal bleeding	Same as IA
IIA	Definite NEC — mildly ill	Same as stage I	Stage I findings with absent bowel sounds and possible abdominal tenderness	Intestinal dilatation or ileus with pneumatosis intestinalis
IIB	Definite NEC — moderately ill	Stage I findings with mild metabolic acidosis and mild thrombocytopenia	Absent bowel sounds, definite tenderness, with possible abdominal wall cellulitis or right lower-quadrant mass	IIA findings with portal venous gas and possible ascites
IIIA	Advanced NEC — severely ill, bowel intact	IIB findings with hypotension, bradycardia, severe apnoea, respiratory or metabolic acidosis, disseminated intravascular coagulation or neutropenia	Generalised peritonitis with marked abdominal tenderness and distension	IIB findings with definite ascites but no pneumoperitoneum
IIIB	Advanced NEC — severely ill, bowel perforated	Same as IIIA	Same as IIIA	Pneumoperitoneum indicating intestinal perforation

How to use it

Stage I represents suspected NEC with non-specific clinical and radiographic findings.
Stage II represents definite NEC; pneumatosis intestinalis establishes stage IIA, while portal venous gas with greater systemic illness supports stage IIB.
Stage III represents advanced NEC with severe systemic illness and peritonitis.
The defining distinction between stages IIIA and IIIB is an intact bowel versus radiographic evidence of perforation.
Staging requires integration of serial clinical, laboratory and imaging findings rather than interpretation of a single radiograph.

Common mistake

Do not classify all portal venous gas or ascites as stage III. Portal venous gas is included in stage IIB, whereas pneumoperitoneum defines stage IIIB.

Exam pearl

Remember the radiographic progression: non-specific ileus in stage I, pneumatosis in IIA, portal venous gas in IIB, definite ascites in IIIA and pneumoperitoneum in IIIB.

Viva questions

What is the Modified Bell classification used for?: It grades the severity of neonatal necrotising enterocolitis using systemic, intestinal and radiographic findings.
How many stages are included in the Modified Bell classification?: There are six substages: IA, IB, IIA, IIB, IIIA and IIIB.
Which finding distinguishes stage IB from stage IA?: Stage IB has gross rectal bleeding, whereas stage IA may have only occult blood in the stool.
Which radiographic finding establishes definite NEC at stage IIA?: Pneumatosis intestinalis establishes definite NEC and is the characteristic radiographic finding of stage IIA.
At which Modified Bell stage is portal venous gas encountered?: Portal venous gas is included in stage IIB, usually with pneumatosis intestinalis and possible ascites.
What distinguishes stages IIIA and IIIB?: In stage IIIA the bowel remains intact, whereas stage IIIB has intestinal perforation demonstrated by pneumoperitoneum.
Does the absence of pneumoperitoneum exclude advanced or perforated NEC?: It does not exclude advanced NEC, because stage IIIA has severe disease without perforation. Clinically suspected perforation may also require further assessment despite an equivocal radiograph.
What is the radiographic progression to remember in Modified Bell staging?: The sequence is non-specific ileus, pneumatosis intestinalis, portal venous gas, definite ascites and finally pneumoperitoneum.