Crohn stricture, fistula, abscess and obstruction

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Crohn strictures arise from variable mixtures of oedema, active inflammation, smooth-muscle hypertrophy and fibrosis. Medical control may reduce the inflammatory component, but established scar cannot be assumed to resolve. Imaging must define length, calibre, upstream bowel and penetrating extensions; endoscopic access adds biopsy when safe. A new colonic or anastomotic stricture also raises dysplasia and cancer concern.

Penetrating disease creates sinus tracts, fistulae and abscesses. The first principle is control of sepsis: antibiotics support treatment, but a sizeable accessible collection needs drainage and an undrained abscess is unsafe territory for immunosuppression escalation. Once physiology improves, joint planning weighs limited resection, bowel-preserving strictureplasty and endoscopic dilatation against recurrence, operative risk and the length of healthy intestine that must remain.

Key points

Use CT in an acute obstructive or septic presentation; use MRE or intestinal ultrasound for planned small-bowel mapping and reduced cumulative radiation.
Describe each stricture by site, length, upstream dilatation, inflammatory features, accessibility, angulation, penetrating disease and cancer concern rather than calling it simply active Crohn.
Drain an accessible Crohn abscess radiologically where possible and, if the patient improves, avoid definitive surgery for at least two weeks while nutrition and medicines are optimised.
Endoscopic balloon dilatation suits selected ileocolonic anastomotic strictures shorter than 4 cm without sharp angulation or penetrating disease; repeated dilatation is often required.
Strictureplasty preserves bowel for small-bowel strictures shorter than 10 cm and is useful with multiple lesions or limited remaining length; fistula-associated abscess and suspected cancer are contraindications.
Resection removes a short diseased segment, phlegmon or cancer-suspect stenosis, but cumulative resections create bile-salt diarrhoea, B12 deficiency and short-bowel risk.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Repeated transmural inflammation

Cycles of ulceration and healing produce muscular hypertrophy and collagen deposition, while deep penetrating injury seeds fistulae and abscesses.

Postoperative recurrence

Crohn inflammation commonly returns near an ileocolonic anastomosis and can progress to anastomotic narrowing despite earlier resection.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Mixed stenotic tissue
Inflammatory oedema, smooth-muscle thickening and fibrotic matrix combine in variable proportions, so a stricture may only partly respond to drugs.
2
Upstream pressure
Luminal narrowing causes stasis, bacterial overgrowth and pre-stenotic dilatation, leading to colic, vomiting and eventually complete obstruction.
3
Transmural penetration
Deep ulceration creates sinus tracts that enter adjacent bowel, bladder, skin or mesentery, where contamination becomes an abscess.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Partial obstruction

Postprandial cramping, bloating, borborygmi, nausea and intermittent vomiting with continued flatus suggest a narrowing that is not yet complete.

Complete obstruction

Persistent vomiting, marked distension and failure to pass stool or flatus indicate high-grade blockage and require urgent fluid, electrolyte and surgical assessment.

Abscess pattern

Fever, rigors, focal tenderness, painful mass and raised inflammatory markers suggest a walled collection beside penetrating diseased bowel.

Internal fistula

Recurrent urinary infection or pneumaturia suggests enterovesical communication, while diarrhoea and malnutrition may follow bypass through an enteroenteric fistula.

External fistula burden

Enterocutaneous drainage volume, content, skin damage and nutritional loss determine urgency alongside the underlying bowel anatomy and sepsis.

Red flags requiring action

Colicky pain becoming constant with guarding, rebound, fever or lactate rise suggests strangulation, perforation or abscess and requires immediate surgical reassessment.
Bilious vomiting, marked distension, absolute constipation and worsening renal function indicate high-grade obstruction and dangerous fluid sequestration.
A tender abdominal or perianal mass with rigors and immunosuppression suggests a collection that needs imaging and drainage rather than a higher immunosuppressive dose.
High-output enterocutaneous fistula with dehydration, electrolyte loss, skin injury or falling weight requires fluid, nutrition and sepsis control before reconstruction.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Contrast CT abdomen and pelvisFirst step
Why
define an acute transition point, bowel compromise, abscess, fistula, perforation and another surgical cause.
Interpretation and limitations
Rim-enhancing fluid or gas-containing collection supports abscess; reduced enhancement, closed-loop configuration, free gas or ascites can signal urgent bowel compromise.
02
MR enterography or intestinal ultrasound
Why
map planned small-bowel strictures and penetrating disease without repeated ionising radiation.
Interpretation and limitations
Length, mural enhancement, oedema, pre-stenotic dilatation and fistulae guide planning, although no modality perfectly separates inflammation from irreversible fibrosis.
03
Ileocolonoscopy with biopsies when safe
Why
inspect accessible ileocolonic or anastomotic narrowing and exclude dysplasia or carcinoma.
Interpretation and limitations
Do not force a tight stenosis; an impassable, ulcerated or asymmetric lesion may need surgical diagnosis even when superficial biopsies are benign.
04
FBC, CRP, U&E, albumin and lactate
Why
measure sepsis, losses, renal injury, nutrition-related risk and possible tissue hypoperfusion.
Interpretation and limitations
Albumin falls with inflammation as well as poor intake; rising lactate or renal deterioration strengthens the need for urgent source control.
05
Drain fluid microbiology
Why
identify organisms after radiological or operative abscess drainage and permit focused antibiotics.
Interpretation and limitations
Culture guides narrowing of treatment, while poor drain output or persistently high CRP prompts tube check and repeat imaging.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Adhesional obstruction

Previous surgery can cause a transition point remote from active Crohn disease, without mural inflammation at the obstructed segment.

Colorectal or small-bowel cancer

A new asymmetric or rapidly progressive stenosis, particularly with anaemia or weight loss, requires tissue and oncological assessment.

Functional pain overlap

Cramping and altered stool may persist without active inflammation or fixed narrowing, but structural complications must be excluded before assigning this label.

Appendiceal or diverticular sepsis

Right-sided appendiceal disease and left-sided diverticulitis can create phlegmon or abscess that resembles penetrating Crohn disease on symptoms alone.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Worked case: ileal stricture with abscessControl sepsis, then perform safer definitive surgeryFirst stepDefinitiveA 28-year-old weighing 72 kg with terminal ileal Crohn disease has fever 38.5°C, pulse 112/min, right iliac fossa tenderness, CRP 198 mg/L and 8 kg weight loss. CT shows a 6 cm ileal stricture, proximal dilatation and a separate safely accessible 4 cm abscess, without free perforation.

1Treat intra-abdominal sepsis with intravenous fluid and blood cultures. Confirm no penicillin hypersensitivity, no previous severe immediate reaction to another beta-lactam, no previous co-amoxiclav-associated jaundice/hepatic injury and creatinine clearance above 30 mL/min. Start co-amoxiclav 1 g/200 mg IV every 8 hours over 30–40 minutes, review at 48 hours against cultures and local resistance data, withhold the next biologic dose and involve interventional radiology, gastroenterology and colorectal surgery.
2Drain the 4 cm collection percutaneously, sending 45 mL of pus for culture; adjust antibiotics to the isolated E coli and monitor drain output, observations, renal function and CRP.
3After resuscitation and percutaneous source control, assess obstruction and gut function the same day. Because liquids pass without vomiting, the dietitian starts low-residue oral supplements on day 1 and records energy and protein delivery; day-ten CRP 36 mg/L and CT residual cavity 9 mm are reassessment results, not a reason nutrition was withheld until day 10.
4Wait beyond two weeks after successful drainage because there is no peritonism or ischaemia, then perform limited ileocaecal resection addressing the fibrotic stricture and penetrating source without sacrificing unrelated small bowel.
5Pathology shows fibrostenotic and penetrating Crohn disease with no dysplasia; six weeks later the patient eats without vomiting, has gained 3 kg and CRP is 6 mg/L. Verify postoperative recurrence-prevention and B12 monitoring plans.

02Short anastomotic narrowingUse selected balloon dilatation with a recurrence planA 39-year-old has intermittent obstructive symptoms four years after ileocaecal resection. MRE and ileocolonoscopy show a 2.5 cm ileocolonic anastomotic stricture, no sharp angulation, no fistula or abscess and biopsies without dysplasia.

1Confirm the short length, endoscopic accessibility, benign biopsies and absence of penetrating disease; discuss that balloon dilatation may defer surgery but often needs repetition.
2Review anticoagulation, perforation risk and availability of surgical rescue, then perform graded endoscopic balloon dilatation through a wire-guided controlled technique in an experienced unit.
3Observe for pain, tachycardia, bleeding and peritonism after the procedure; new severe pain would trigger urgent CT for perforation rather than planned discharge.
4The lumen is dilated sufficiently to permit careful scope passage and symptoms resolve. At three months the patient eats normally and MRE shows less upstream dilatation.
5Document that recurrence may require repeat dilatation or limited resection and continue objective Crohn activity assessment rather than injecting intralesional corticosteroid, which BSG advises has no role.

03Multiple short small-bowel stricturesPreserve length with planned strictureplastyA 45-year-old with two previous resections has four jejunal strictures measuring 2–6 cm, recurrent partial obstruction, no abscess or internal fistula and only 170 cm of small bowel estimated to remain.

1Use enterography to map every lesion and review prior operation notes so the team understands the cumulative bowel-length risk and does not plan another blind segmental resection.
2Optimise anaemia and nutrition and explain recurrence, leak, bleeding and the possibility that an unexpected malignant or fistulating lesion will require resection instead.
3At laparotomy confirm four non-penetrating short strictures with no suspicious mass; perform bowel-preserving strictureplasties and measure the retained small-bowel length.
4Test luminal patency and inspect repair perfusion, then record the technique and exact site of each repair to make future imaging interpretable.
5At eight-week review weight is stable, vomiting has ceased and haemoglobin has risen from 101 to 124 g/L; verify medicine optimisation and imaging or calprotectin follow-up for recurrence.

Key medicines and prescribing safety1 treatment · regimens, roles and cautions

One implementable empirical UK product example for intra-abdominal infection while image-guided drainage supplies definitive abscess source control; local resistance or allergy may require a different regimen.

Co-amoxiclav 1000 mg/200 mg injection/infusion for the worked Crohn abscess

For this adult over 40 kg with creatinine clearance above 30 mL/min and no relevant beta-lactam allergy, give 1000 mg/200 mg IV every 8 hours, infused over 30–40 minutes. Review at 48 hours after drainage and narrow to cultures/local susceptibility; do not continue beyond 14 days without a new clinical review. For CrCl 10–30 mL/min the product uses an initial 1000/200 mg then 500/100 mg twice daily, and below 10 mL/min an initial 1000/200 mg then 500/100 mg every 24 hours.

Do not give to a patient with penicillin hypersensitivity, a previous severe immediate hypersensitivity reaction to another beta-lactam, or previous co-amoxiclav-associated jaundice/hepatic injury. Monitor renal and hepatic function, urine output and culture response; review warfarin/INR, methotrexate and probenecid interactions and the vial’s sodium/potassium load.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Complete obstruction

Progressive luminal loss causes vomiting, fluid sequestration, electrolyte disturbance, acute renal injury and eventual pressure-related bowel perforation.

Intra-abdominal sepsis

An abscess may enlarge, rupture or seed bloodstream infection, especially when drainage is delayed during immune suppression.

Short-bowel syndrome

Cumulative resections reduce absorptive surface, causing fluid, electrolyte and nutrient dependence that may progress to intestinal failure.

Fistula-related organ injury

Enterovesical fistula causes urinary infection and pneumaturia, while enterocutaneous output damages skin and depletes fluid and protein.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

After drainage, chart physiology, pain, drain volume and character, CRP, renal function and culture; repeat imaging if the expected fall in sepsis markers does not occur.
During non-operative stricture treatment record vomiting, ability to eat, stool or flatus, weight and pre-stenotic dilatation, because symptom suppression alone does not prove luminal recovery.
After balloon dilatation provide immediate perforation safety-netting and planned review for recurrent obstructive symptoms, acknowledging that repeat procedures are common.
After resection or strictureplasty document remaining bowel length, anastomoses, repair sites and pathology, then monitor B12, iron, vitamin D and bile-salt diarrhoea according to anatomy.
Use endoscopic, biochemical and cross-sectional assessment to manage ongoing inflammatory activity separately from the mechanical result of the procedure.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Abscess changes the sequence

Drainage and antibiotics precede escalation of immune treatment, while successful control creates time for nutrition and planned rather than septic surgery.

Fibrosis has no blood test

CRP may fall while a fixed scar continues to obstruct; anatomy and symptoms decide whether a mechanical intervention is still needed.

Dilatation has selection limits

Short, straight, non-penetrating anastomotic strictures are safer targets than long, sharply angled, ulcerated or fistulating lesions.

Length is a clinical asset

Strictureplasty and limited resection protect absorptive capacity in people who may need further operations during a lifetime of Crohn disease.

Biopsy has sampling limits

Benign superficial tissue from a stenosis cannot always exclude deeper cancer when imaging and behaviour remain suspicious.

11Common pitfallsFrequent interpretation and management errors.

01
Escalating a biologic while a febrile collection remains undrained confuses inflammatory control with control of infection.
02
Treating every Crohn narrowing with corticosteroid ignores fixed fibrosis and can postpone relief of recurrent obstruction.
03
Balloon dilatation of a long angulated stricture with adjacent fistula exposes the patient to perforation without durable benefit.
04
Performing repeated generous resections without measuring remaining bowel risks later short-bowel intestinal failure.
05
Assuming an anastomotic stricture is benign without biopsy or pathological assessment can miss dysplasia or recurrent malignancy.

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