What is the most likely cause and initial management for a painful hard periumbilical mass in a 13‑year‑old female with celiac disease, chronic constipation, poor nutrition, normal abdominal CT and X‑ray, and evidence of colonic inflammation?

Most Likely Diagnosis: Fecal Impaction with Possible Celiac-Related Complications

The hard periumbilical lump is most likely a fecal impaction (stool mass) given her chronic constipation history, and the colonic inflammation suggests ongoing celiac disease activity despite presumed treatment, requiring immediate verification of gluten-free diet adherence and consideration of additional gastrointestinal pathology.

Diagnostic Reasoning

Primary Consideration: Fecal Impaction

• A palpable hard periumbilical mass with normal CT and X-ray in a patient with chronic constipation strongly suggests fecal impaction
• The "normal" imaging may have missed subtle findings or the mass may be predominantly stool that wasn't recognized as pathologic
• Constipation is common in celiac disease patients, particularly those with poor dietary adherence or malnutrition

Celiac Disease Complications to Address

The combination of celiac disease, poor nutrition, and colonic inflammation raises several concerns:

Verify Gluten-Free Diet Adherence:

• Poor eating habits in a 13-year-old with celiac disease suggests possible non-adherence to gluten-free diet 1
• Teenagers are notably less adherent to gluten-free diets and less satisfied with disease impact 1
• Check tissue transglutaminase antibodies (TG2-IgA) to assess dietary compliance 2, 3

Colonic Inflammation Considerations:

• Celiac disease can be associated with microscopic colitis, which presents with colonic inflammation 4
• The coexistence of immune-mediated small bowel and colonic inflammatory diseases is recognized but underdiagnosed 4
• However, this typically presents with diarrhea rather than constipation

Immediate Management Algorithm

Step 1: Address the Acute Mass

• Manual disimpaction if accessible on rectal exam
• Aggressive bowel regimen: polyethylene glycol (PEG) 1-1.5 g/kg/day (maximum 17g daily)
• Consider enemas if oral therapy insufficient
• Ensure adequate hydration

Step 2: Verify Celiac Disease Control

• Check TG2-IgA levels immediately 2, 3
• Detailed dietary history focusing on gluten exposure
• Assess for nutritional deficiencies: CBC, iron studies, vitamin D, calcium, folate, B12 5
• Consider repeat upper endoscopy with duodenal biopsies if serology suggests ongoing gluten exposure 3

Step 3: Investigate Colonic Inflammation

• If symptoms persist after addressing constipation and celiac control, consider colonoscopy with biopsies to evaluate for:
  • Microscopic colitis (lymphocytic or collagenous) 4
  • Concurrent inflammatory bowel disease (rare but reported) 6
• This is particularly important given the documented colonic inflammation

Step 4: Nutritional Rehabilitation

• Referral to dietitian experienced in celiac disease 2, 1
• Address malnutrition with appropriate supplementation
• Monitor growth parameters closely (weight and height percentiles) 1

Critical Pitfalls to Avoid

Don't assume imaging is truly "normal":

• Request radiologist re-review specifically for stool burden
• Fecal impaction can be subtle on imaging

Don't overlook celiac non-adherence in adolescents:

• This age group has the highest non-compliance rates 1
• Non-adherence leads to persistent symptoms, malabsorption, and complications 1

Don't miss rare but serious associations:

• While unlikely given normal CT, intussusception can occur as first manifestation of celiac disease in children 7
• Consider if symptoms worsen or become more acute

Don't delay colonoscopy if symptoms persist:

• The documented colonic inflammation needs explanation 4
• Concurrent microscopic colitis or early inflammatory bowel disease must be excluded if conservative management fails

Follow-Up Strategy

• Immediate (1-2 weeks): Reassess after bowel cleanout, verify symptom resolution
• 1 month: Check TG2-IgA results, nutritional labs, growth parameters
• 3-6 months: Regular monitoring per celiac guidelines with serology and clinical assessment 2, 1
• Consider GI referral if mass persists, symptoms worsen, or celiac serology remains elevated despite reported dietary adherence

The key is recognizing that this presentation likely represents the intersection of inadequate celiac disease management (leading to malnutrition and poor gut motility) and severe constipation, rather than a sinister mass lesion.