Diverticular fistula and stricture

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

Fistula and stricture are structural consequences of transmural inflammation. A sigmoid phlegmon can adhere to bladder, vagina or another bowel loop before eroding into it, while repeated injury and healing can contract into a fixed narrowing. These complications create characteristic syndromes, but diverticula do not prove benignity because colorectal cancer and Crohn disease can cause similar anatomy.

CT defines the diseased segment, adjacent organs, collections, ureters and upstream dilatation. Endoscopic and organ-specific assessment then address malignancy when they can be performed safely. Active urosepsis or obstruction is treated first. Once inflammation and physiology are controlled, continuing symptoms from a fistula or stricture provide a clear reason to discuss elective sigmoid resection, adjacent-organ repair and possible stoma.

Key points

Pneumaturia, faecaluria and recurrent mixed enteric urinary infection strongly suggest a colovesical fistula when recent bladder instrumentation is absent.
Passage of gas or faeces through the vagina, often after hysterectomy, can reveal a colovaginal communication.
Progressive colic, bloating, reduced stool calibre and constipation suggest a fixed stricture, but cancer must be excluded.
Contrast CT maps adherent organs, intravesical gas, collections, ureteric involvement and proximal bowel dilatation; the tract itself may not be visible.
Investigate the colon and affected adjacent organ safely before planned resection, recognising that a non-traversable stricture leaves residual cancer uncertainty.
Continuing fistula or stricture symptoms after recovery from complicated diverticulitis support consideration of elective open or laparoscopic resection.

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

Inflammatory adhesion and erosion

A contained sigmoid perforation adheres to bladder, vagina or bowel before chronic inflammation creates an abnormal communication.

Fibrotic repair

Repeated mural inflammation heals with collagen deposition, muscular thickening and contraction that shorten and narrow the affected segment.

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

1
Enterovesical contamination
Colonic pressure drives gas and enteric organisms into the bladder, causing pneumaturia, faecaluria and recurrent polymicrobial urinary infection.
2
Fixed mechanical narrowing
Scar contraction restricts faecal passage, producing colic and proximal dilatation before complete obstruction or pressure-related perforation develops.
3
Malignant mimicry
A colorectal tumour can invade an adjacent organ or form an annular stricture, creating anatomy indistinguishable from benign inflammation.

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

Fistula formation

Contained perforation adheres sigmoid to bladder, vagina or another bowel loop before erosion establishes an epithelialised communication.

Stricture formation

Repeated inflammation and healing deposit collagen, progressively narrowing the sigmoid lumen and impairing transit.

Urinary consequence

Colovesical contamination produces recurrent polymicrobial infection, bladder inflammation and sometimes upper-tract sepsis.

Red flags requiring action

Pneumaturia or faecaluria with fever, hypotension or flank pain indicates enterovesical contamination complicated by urinary sepsis.
Absolute constipation, vomiting and increasing distension suggest complete obstruction at a diverticular or malignant stricture.
Generalised guarding or free intraperitoneal gas indicates perforation and requires emergency rather than interval operative planning.

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 pelvisFirst step
Why
map fistula, inflammation and obstruction.
Interpretation and limitations
Intravesical gas without instrumentation supports colovesical fistula; CT may not show the tract directly.
02
Colonoscopy after acute inflammation settles
Why
exclude mucosal cancer and assess stricture.
Interpretation and limitations
A non-traversable narrowing remains incompletely assessed and may require CT colonography or operative pathology.
03
Urine culture and renal profile
Why
document infection and organ effect.
Interpretation and limitations
Mixed enteric organisms support contamination but do not define anatomy.
04
Cystoscopy or gynaecological assessment
Why
exclude organ-specific malignancy and plan repair.
Interpretation and limitations
These tests complement rather than replace colonic investigation.

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

Colorectal cancer

Malignant invasion can cause fistulation or narrowing; diverticula beside the lesion and negative superficial biopsies do not establish benignity.

Crohn disease

Transmural Crohn inflammation can produce multiple fistulae and stenoses, often with small-bowel, skip or perianal disease elsewhere.

Radiation or surgical injury

Previous pelvic radiotherapy or anastomotic injury can create fistulae and strictures with poor tissue quality and different reconstructive needs.

Additional chapter-specific clues

Cancer mimic

Both colorectal cancer and diverticular inflammation can invade adjacent organs or narrow bowel, making histological exclusion essential.

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

01Worked case: colovesical fistula after diverticulitisConfirm anatomy, exclude cancer and verify repairFirst stepA 69-year-old has pneumaturia, recurrent cultures growing Escherichia coli and Klebsiella, and CT showing thickened sigmoid adherent to a gas-containing bladder. There has been no catheterisation and renal function is stable.

1Treat the current urinary infection according to culture and check for fever, hypotension, hydronephrosis or abscess that would require urgent drainage or decompression.
2Review CT with colorectal and urology teams to map the sigmoid-bladder interface, ureteric proximity and absence of a drainable collection.
3After inflammation settles, colonoscopy excludes a mucosal tumour and cystoscopy shows inflammatory oedema without bladder cancer; explain that the tract need not be directly visualised.
4Undertake elective sigmoid resection with separation and repair of the bladder defect, after consent for ureteric injury, anastomotic leak and temporary stoma.
5Histology confirms diverticular inflammation without malignancy, a postoperative cystogram shows no urinary leak, and at six weeks pneumaturia and urinary infection have resolved.

02Non-traversable sigmoid stricturePlan resection while retaining malignant uncertaintyA 63-year-old has progressive colic, constipation and a 5 kg weight loss. CT shows a short sigmoid stricture with proximal dilatation and diverticula, but no complete obstruction; colonoscopy cannot pass the narrowing and biopsies are non-diagnostic.

1Recognise that weight loss and an incomplete luminal assessment prevent the label benign diverticular stricture from being accepted as certain.
2AlternativeComplete staging-quality CT review and assess the remaining colon by a safe alternative where feasible, without forcing the colonoscope through inflamed narrowing.
3Discuss the case at the colorectal multidisciplinary meeting and plan an oncological sigmoid resection because malignancy cannot be excluded preoperatively.
4Resect the narrowed segment with appropriate vascular and nodal clearance and send the intact specimen for full histopathological assessment.
5Pathology shows dense diverticular fibrosis, no tumour and 18 benign lymph nodes; document restored bowel transit and the final benign diagnosis at follow-up.

03Fistula complicated by urinary sepsisStabilise infection before definitive elective repairDefinitiveA patient awaiting colovesical fistula surgery develops rigors, temperature 39.4°C, blood pressure 88/52 mmHg, creatinine 210 micromol/L and CT evidence of left hydronephrosis beside an inflammatory pelvic mass.

1Treat septic shock immediately with cultures, intravenous antibiotics, fluid, urine-output monitoring and critical-care support while colorectal and urology teams attend.
2Identify obstruction of the left ureter as an additional source problem rather than assuming antibiotics alone will restore drainage.
3Decompress the collecting system urgently by the safest urological route and drain any accessible pelvic collection shown on CT.
4DefinitiveOnce blood pressure, kidney function and infection recover, restage the fistula anatomy and re-plan definitive sigmoid and bladder surgery rather than operating electively during shock.
5Verify acute control by negative repeat blood cultures, creatinine returning to 112 micromol/L and resolution of hydronephrosis before proceeding to reconstruction.

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

Recurrent urosepsis

Ongoing bowel-bladder contamination repeatedly seeds the urinary tract and can progress to pyelonephritis, renal obstruction or septic shock.

Complete large-bowel obstruction

Progressive stricture can stop stool and flatus, causing vomiting, marked dilatation, bowel ischaemia and eventual perforation.

Nutritional and renal decline

Chronic infection, reduced intake and obstructive uropathy can cause weight loss, anaemia and kidney injury before definitive repair.

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

Repeat urine culture after treating infection and track fever, renal function and hydronephrosis; recurrent antibiotics alone do not correct bowel-bladder communication.
Ask directly about pneumaturia, faecaluria and vaginal gas or stool because embarrassment may prevent spontaneous disclosure of the most discriminating symptoms.
Monitor stool and flatus, colic, distension and vomiting while a stricture is being evaluated; absolute constipation requires emergency reassessment.
After surgery, confirm histopathology, urinary integrity, renal recovery, bowel function and whether fistula symptoms have actually resolved.

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

Pneumaturia is highly informative

Gas in urine without recent instrumentation should prompt assessment for an enterovesical connection.

A tract need not be seen

Indirect CT findings plus the clinical syndrome can establish high probability even when the fistula itself is not visualised.

Stricture demands cancer exclusion

Benign inflammatory narrowing and annular cancer can look similar and carry different operative implications.

En-bloc thinking protects planes

Separation or biopsy through an adherent malignant lesion can breach oncological tissue and contaminate the field.

11Common pitfallsFrequent interpretation and management errors.

01
Treating every recurrent urinary infection without asking about pneumaturia can miss a colovesical fistula.
02
Passing a colonoscope forcefully through a tight inflamed stricture risks perforation.
03
Assuming CT-proven diverticula make a stricture benign can delay cancer diagnosis.
04
Scheduling elective surgery before controlling sepsis and nutrition increases avoidable morbidity.

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