What are the causes of vomiting with constipation in a 12‑month‑old infant?

Causes of Vomiting with Constipation in a 1-Year-Old

In a 12-month-old with vomiting and constipation, the most critical immediate concern is to determine whether the vomiting is bilious, which indicates intestinal obstruction and constitutes a surgical emergency requiring immediate imaging and surgical consultation. 1, 2

Immediate Red-Flag Assessment

The first priority is to characterize the vomitus and assess for surgical emergencies:

• Bilious (green) vomiting at any age is a surgical emergency until proven otherwise, with malrotation with midgut volvulus being the most critical consideration that can cause intestinal necrosis within hours 1, 2, 3
• Non-bilious vomiting with constipation suggests either functional constipation causing gastric distention and secondary vomiting, or less urgent obstructive processes 2, 4
• Document stool pattern carefully: absent stools, "currant-jelly" stools (suggesting intussusception), or hard infrequent stools (suggesting functional constipation) 2, 5

Primary Differential Diagnosis

Life-Threatening Surgical Causes

Intussusception (peak age 6-18 months):

• Presents with intermittent crampy abdominal pain manifested as episodes of inconsolable crying or drawing up of legs 1
• "Currant-jelly" stools indicate mucosal damage, though may be a late finding 1, 5
• Palpable abdominal mass may be present 5
• Ultrasound is the initial imaging modality of choice when clinical features suggest intussusception 2

Malrotation with midgut volvulus:

• Accounts for 20% of bilious vomiting cases and requires immediate upper GI series 2, 3
• Can present at any age, not just newborns 1, 2
• Plain abdominal radiograph may be normal in up to 7% of cases, so bilious vomiting mandates upper GI series even with normal X-ray 2

Common Non-Surgical Causes

Functional constipation with secondary vomiting:

• Constipation affects 5-10% of pediatric patients and is the second most common reason for pediatric gastroenterology referral 6
• Severe fecal impaction can cause gastric distention and non-bilious vomiting 7, 8
• Often begins after a painful bowel movement, leading to stool-withholding behavior 6

Viral gastroenteritis:

• Most common cause of acute vomiting in children, typically with watery diarrhea 2, 4
• However, constipation is not typical of gastroenteritis; if present, consider alternative diagnoses 2

Diagnostic Algorithm

Step 1: Characterize the Vomitus

• If bilious: Obtain abdominal radiograph immediately as first imaging study, followed by upper GI series to evaluate for malrotation 1, 2
• If non-bilious: Proceed to clinical assessment for intussusception versus functional constipation 2, 3

Step 2: Assess for Intussusception Features

• Intermittent inconsolable crying or leg-drawing episodes 1
• Bloody or "currant-jelly" stools 1, 5
• Palpable abdominal mass 5
• Lethargy between episodes 7
• If present: Obtain abdominal ultrasound immediately 2

Step 3: Evaluate Hydration and Toxicity

• Severe dehydration (≥10% fluid deficit): prolonged skin tenting >2 seconds, cool extremities, decreased capillary refill, lethargy requires immediate IV resuscitation 2
• Toxic appearance with fever may indicate sepsis, meningitis, urinary tract infection, or pneumonia 2, 4

Step 4: Consider Functional Constipation

• History of hard, infrequent stools with stool-withholding behavior 6
• Abdominal distention on examination 7
• Non-bilious vomiting secondary to gastric distention from severe impaction 8
• Abdominal radiograph may show stool burden but is not always necessary for diagnosis 6

Critical Pitfalls to Avoid

• Never dismiss bilious vomiting as "just gastroenteritis"—it requires immediate surgical evaluation 1, 2, 4
• Abdominal radiographs can be normal in children with intussusception and even early malrotation with volvulus, so clinical suspicion must drive imaging decisions 2, 7
• Young children may appear playful between paroxysmal episodes of intussusception, leading to false reassurance 7
• Constipation can coexist with serious pathology; do not assume constipation explains all symptoms without excluding surgical emergencies 7, 8
• Antidiarrheal agents are contraindicated in children and can cause severe abdominal distention, ileus, and death 2

Management Priorities

• Any bilious vomiting: NPO (nothing by mouth), nasogastric tube decompression, immediate surgical consultation 4
• Suspected intussusception: Immediate ultrasound and surgical consultation for possible pneumatic or hydrostatic reduction 1, 2
• Functional constipation with vomiting: Disimpaction followed by maintenance laxative therapy, but only after excluding surgical causes 6
• Dehydration: Oral rehydration therapy for mild-moderate cases; IV fluids for severe dehydration 2
• Persistent vomiting preventing oral intake: Ondansetron 0.2 mg/kg orally (maximum 4 mg) may be used, but does not replace proper fluid management 2, 4