Ulcerative Colitis

Slide 1 · Ulcerative Colitis

Inflammatory bowel disease: mechanisms, morphology and clinicopathologic interpretation

A pathology teaching lecture

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Identify the characteristic continuous, rectum-based distribution of ulcerative colitis.

Explain the immune, microbial and epithelial components of the multifactorial pathogenesis.

Recognize gross and microscopic evidence of activity and chronic mucosal injury.

Distinguish ulcerative colitis from Crohn disease and discuss major complications.

Slide 3 · Definition: Chronic inflammatory disease of the colon

Ulcerative colitis is a chronic, relapsing form of inflammatory bowel disease.

Inflammation extends continuously proximally from the rectum.

Disease primarily involves the mucosa, with superficial submucosal extension in severe cases.

The usual distribution is confined to the colon and rectum.

Slide 4 · Ulcerative colitis in the inflammatory bowel disease spectrum

Feature

Ulcerative colitis

Crohn disease

Principal site

Colon and rectum

Any gastrointestinal site

Typical pattern

Continuous

Discontinuous (“skip”)

Inflammatory depth

Mucosal

Often transmural

Typical complication

Severe colitis / toxic megacolon

Stricture / fistula

Slide 5 · Distribution begins at the rectum

Segmental map of large bowel (schematic)

Rectum

Sigmoid

Descending

Transverse

Ascending

Cecum

Distal → proximal

Involved mucosa

Inflammation is continuous; Normal bowel is not ordinarily interposed between diseased segments.

Colored segments convey disease distribution, not anatomical shape or segment length.

Slide 6 · Ulcerative proctitis: Disease confined distally

Segmental map of large bowel (schematic)

Rectum

Sigmoid

Descending

Transverse

Ascending

Cecum

Distal → proximal

Involved mucosa

Proctitis describes ulcerative colitis restricted to the rectum.

Colored segments convey disease distribution, not anatomical shape or segment length.

Slide 7 · Proctosigmoiditis and left-sided colitis

Segmental map of large bowel (schematic)

Rectum

Sigmoid

Descending

Transverse

Ascending

Cecum

Distal → proximal

Involved mucosa

Distal phenotypes may involve rectum and sigmoid or extend through the descending colon.

Colored segments convey disease distribution, not anatomical shape or segment length.

Slide 8 · Pancolitis: Extensive colonic involvement

Segmental map of large bowel (schematic)

Rectum

Sigmoid

Descending

Transverse

Ascending

Cecum

Distal → proximal

Involved mucosa

Pancolitis denotes involvement of the entire colon; It is relevant to complications and surveillance.

Colored segments convey disease distribution, not anatomical shape or segment length.

Slide 9 · Backwash ileitis does not imply Crohn disease

The small bowel is usually spared in ulcerative colitis.

Mild distal ileal mucosal inflammation can accompany severe pancolitis.

This phenomenon is termed backwash ileitis.

Interpret ileal inflammation alongside colonic distribution and overall morphology.

Slide 10 · Cecal red spot: An important distribution caveat

Segmental map of large bowel (schematic)

Rectum

Sigmoid

Descending

Transverse

Ascending

Cecum

Distal → proximal

Involved mucosa

A focal appendiceal/cecal focus may accompany left-sided ulcerative colitis without typical Crohn-type skip disease.

Colored segments convey disease distribution, not anatomical shape or segment length.

Slide 11 · Epidemiology and clinical onset

Ulcerative colitis commonly presents in adolescence or early adulthood but can begin at any age.

Inflammatory bowel disease is prevalent in North America, northern Europe and Australia.

Incidence is also rising in regions where inflammatory bowel disease was historically uncommon.

Population and environmental trends support a contribution from host–environment interactions.

Slide 12 · Multifactorial pathogenesis: Interacting systems

Polygenic susceptibility

Host–microbial interactions

Mucosal immune dysregulation

Sustained epithelial injury

No single pathogen or single-gene model explains ordinary ulcerative colitis.

Schematic causal framework; Associations should not be interpreted as established single-step mechanisms.

Slide 13 · Genetic susceptibility is polygenic

More than 200 inflammatory bowel disease risk alleles have been identified.

Known variants account for only a minority of overall disease risk, particularly in ulcerative colitis.

Many variants are shared by ulcerative colitis and Crohn disease.

Risk loci implicate immune signaling, bacterial responses and host defense.

Slide 14 · Shared genetic architecture does not mean identical risk

Genetic observation

Clinicopathologic significance

Many shared risk polymorphisms

Common inflammatory pathways underlie both disorders

NOD2 susceptibility variants

Strongly linked to Crohn disease, not typical ulcerative colitis

PTPN22 risk variants

Opposing risk directions between the two conditions

Ulcerative colitis extent

May correlate with aggregate genetic associations

Slide 15 · Interpreting genetic association

A genetic association signals susceptibility, not inevitability of disease.

Risk-allele prevalence and effect sizes differ between populations.

Regulatory-region loci may alter expression without changing protein sequence.

Pathology reflects combined genetic, environmental, microbial and immune influences.

Slide 16 · Mucosal immunity: The cellular inflammatory circuit

Luminal microbial signals

Dendritic cells / macrophages

Activated T cells and cytokines

Neutrophilic epithelial injury

This is a conceptual immune circuit; The initiating microbial species remain uncertain.

Schematic causal framework; Associations should not be interpreted as established single-step mechanisms.

Slide 17 · T-cell pathways in inflammatory bowel disease

Th1 and Th17 inflammatory responses are implicated in both major forms of inflammatory bowel disease.

Ulcerative colitis also shows a limited Th2-associated component.

Cytokine-mediated immune recruitment perpetuates epithelial damage.

Morphologic activity is manifested by neutrophils injuring crypt epithelium.

Slide 18 · Therapeutic responses support immune involvement

Cytokines sustain inflammation

Anti-TNF or IL-23–axis therapy

Reduced immune activation

Control of inflammatory activity

Treatment efficacy supports an immune contribution; It does not establish one universal pathogenesis.

Schematic causal framework; Associations should not be interpreted as established single-step mechanisms.

Slide 19 · Microbiome: Dysbiosis is associated with disease

Microbial community shifts

Reduced species diversity in IBD

Altered epithelial–immune crosstalk

Potential inflammation feedback

Whether dysbiosis precedes inflammation or results from it is often unresolved.

Schematic causal framework; Associations should not be interpreted as established single-step mechanisms.

Slide 20 · Microbial findings: Observation versus inference

Observed or proposed

Interpretation

Dysbiosis in patients with IBD

Association documented

Persistent immune responses to commensals

Plausible pathogenic mechanism

Specific universal microbial trigger

Not established

Microbial metabolites modifying immunity

Active area of investigation

Slide 21 · Barrier function links lumen and mucosal immunity

Impaired epithelial protection

Increased mucosal exposure

Immune stimulation

Mucosal inflammation

Epithelial function is one contributor; Barrier data are especially clear in Crohn disease.

Schematic causal framework; Associations should not be interpreted as established single-step mechanisms.

Slide 22 · What remains unknown in ulcerative colitis

Exact triggers of onset in previously healthy individuals are not known.

No single causative organism accounts for the disease.

Dysbiosis may be either cause or consequence of intestinal inflammation.

Immune, barrier and host-genetic models remain incomplete.

Slide 23 · A possible infectious antecedent

Enteric infection

Mucosal immune activation

Microbial ecosystem change

Persistent colitis in susceptible host

Proposed mechanism, not a proven sequence for every patient.

Schematic causal framework; Associations should not be interpreted as established single-step mechanisms.

Slide 24 · Observed environmental associations require caution

Observation

Interpretive caution

Psychological stress can precede disease or relapse

Association does not establish direct etiology

Symptom onset after smoking cessation

Clinical association; Not a recommendation to smoke

Infectious enteritis can precede onset

Possible trigger in a susceptible patient

Regional incidence has increased

Several environmental explanations remain possible

Slide 25 · Gross pathology follows a continuous gradient

Segmental map of large bowel (schematic)

Rectum

Sigmoid

Descending

Transverse

Ascending

Cecum

Distal → proximal

Involved mucosa

The boundary between inflamed and uninvolved colon may be abrupt, despite continuous disease proximally from the rectum.

Colored segments convey disease distribution, not anatomical shape or segment length.

Slide 26 · Active colitis: Red, granular mucosal surface

Schematic, not a gross pathology specimen

Erythema and granularity reflect mucosal inflammation. These changes vary in intensity along the involved colon.

Slide 27 · Ulcerative colitis produces broad-based ulcers

Schematic, not a gross pathology specimen

Ulceration may be extensive and broad based rather than the narrow, deep fissures characteristic of Crohn disease.

Slide 28 · Inflammatory pseudopolyps are regenerative islands

Schematic, not a gross pathology specimen

Residual or regenerating mucosa protrudes between regions of ulceration and is not itself evidence of epithelial neoplasia.

Slide 29 · Mucosal bridges can join pseudopolyps

Schematic, not a gross pathology specimen

The tips of inflammatory polyps may become connected by bridges of residual/regenerating mucosa.

Slide 30 · Chronic mucosal atrophy may erase normal folds

Schematic, not a gross pathology specimen

Repeated mucosal injury and repair can produce a smooth, atrophic surface with reduced normal folding.

Slide 31 · Superficial disease explains the usual normal wall thickness

Mucosa

Submucosa

Muscularis propria

Serosa

Mucosa affected; Deeper wall usually preserved.

Inflammation is primarily mucosal.

Layer cross-section schematic; Relative layer thickness is illustrative.

Slide 32 · Why strictures point toward an alternative diagnosis

Feature

Ulcerative colitis

Crohn disease

Typical bowel-wall fibrosis

Mild / minimal

More prominent

Fibrostenotic narrowing

Uncommon

Characteristic complication

Wall thickening

Not a defining feature

Often substantial

Fistulas

Not characteristic

Common with penetrating disease

Slide 33 · Microscopic inflammation is mainly mucosal

Mucosa

Submucosa

Muscularis propria

Serosa

Lamina propria inflammation with crypt injury dominates.

Inflammation is primarily mucosal.

Layer cross-section schematic; Relative layer thickness is illustrative.

Slide 34 · Inflammatory infiltrates populate the lamina propria

Muscularis mucosae

Illustrative crypt architecture — not a tissue photomicrograph

Microscopic interpretation

Increased mucosal inflammatory cells accompany glandular injury. Assess both chronic inflammation and neutrophilic activity.

Slide 35 · Cryptitis: Neutrophils invade crypt epithelium

Muscularis mucosae

Illustrative crypt architecture — not a tissue photomicrograph

Microscopic interpretation

An active inflammatory change. Neutrophils breach the glandular epithelium and injure epithelial cells.

Slide 36 · Crypt abscess: Neutrophils accumulate in crypt lumina

Muscularis mucosae

Illustrative crypt architecture — not a tissue photomicrograph

Microscopic interpretation

Clusters of neutrophils within gland lumina signify active crypt injury. They are not specific to ulcerative colitis.

Slide 37 · Repeated injury distorts crypt architecture

Muscularis mucosae

Illustrative crypt architecture — not a tissue photomicrograph

Microscopic interpretation

Long-standing injury and regeneration cause abnormal crypt orientation, branching and spacing.

Slide 38 · Metaplastic changes indicate chronic injury

Change

Meaning in chronic colitis

Paneth cell metaplasia in left colon

Paneth cells appear where normally absent

Pseudopyloric metaplasia

Glands resemble gastric antral-type glands

Architectural distortion

Residual evidence of repeated crypt destruction and repair

Mucosal atrophy

Reduced crypt population after longstanding injury

Slide 39 · Paneth cell metaplasia in distal colonic mucosa

Muscularis mucosae

Illustrative crypt architecture — not a tissue photomicrograph

Microscopic interpretation

Paneth cells are normally absent from much of the left colon. Their presence there supports chronic mucosal injury.

Slide 40 · Pseudopyloric metaplasia as a marker of repair

Involved colonic mucosa can show glands with gastric antral-like differentiation.

It emerges in the setting of repeated epithelial injury and regeneration.

It is not an isolated, pathognomonic marker of ulcerative colitis.

Interpret with the distribution and other histologic findings.

Slide 41 · Mucosal atrophy results from prolonged injury

Muscularis mucosae

Illustrative crypt architecture — not a tissue photomicrograph

Microscopic interpretation

Loss of crypts and altered gland spacing may persist after activity decreases. This is a marker of chronic tissue damage.

Slide 42 · Severe ulcers may reach the submucosa

Mucosa

Submucosa

Muscularis propria

Serosa

Severe mucosal destruction can penetrate superficially.

Schematic layer distribution is simplified.

Layer cross-section schematic; Relative layer thickness is illustrative.

Slide 43 · Granulomas are a key differential clue

Finding

Interpretation

Well-formed noncaseating granulomas

Suggest Crohn disease or an alternative granulomatous colitis

Typical ulcerative colitis biopsy

No Crohn-type granulomas expected

Crypt rupture-associated granulomatous reaction

Interpret in an appropriate tissue context

Absent granulomas

Does not by itself exclude Crohn disease

Slide 44 · Recognizing activity versus chronicity

Active inflammation

Chronic injury

Neutrophilic cryptitis

Architectural crypt distortion

Crypt abscesses

Metaplasia of epithelial glands

Surface epithelial injury and ulceration

Crypt loss and mucosal atrophy

Current inflammatory damage

Evidence of prior recurrent damage

Slide 45 · Histologic healing may be incomplete or extensive

Active mucosal injury

Inflammation subsides

Residual chronic changes may remain

Sometimes near-normal architecture

Avoid equating endoscopic remission with obligatory microscopic normalization.

Schematic causal framework; Associations should not be interpreted as established single-step mechanisms.

Slide 46 · Classic symptomatic attack

Bloody diarrhea is often mixed with stringy mucoid material.

Lower abdominal pain and cramping are frequent.

Cramps may be temporarily relieved by defecation.

Attacks may persist for days to months before symptoms subside.

Slide 47 · Why blood and mucus accompany active colitis

Inflamed friable mucosa

Epithelial injury / ulceration

Bleeding and mucous exudate

Bloody, mucoid diarrhea

This mechanistic schema relates the classic clinical finding to observed mucosal injury.

Schematic causal framework; Associations should not be interpreted as established single-step mechanisms.

Slide 48 · Symptoms reflect inflammation of the distal colon

Distal mucosal injury contributes to rectal bleeding and urgency.

Lower abdominal cramping often accompanies active bowel movements.

Rectal involvement is an important clue when clinical findings are interpreted.

The intensity of symptoms can fluctuate across relapses and remissions.

Slide 49 · Relapsing disease: Activity alternates with remission

Active flare

Clinical improvement

Remission

Recurrent flare

The cycle is variable; Individual episodes may last days, weeks or months.

Slide 50 · Disease burden varies substantially

More than half of patients have clinically mild disease description.

However, most patients experience at least one relapse over a ten-year period.

An initial episode can occasionally be severe enough to require urgent care.

Severity must be assessed clinically rather than inferred from the diagnosis alone.

Slide 51 · Life-threatening deterioration requires recognition

Severe active colitis

Extensive mucosal inflammation

Toxic megacolon

Risk of perforation / emergency

Toxic megacolon is an uncommon but important complication of fulminant disease.

Schematic causal framework; Associations should not be interpreted as established single-step mechanisms.

Slide 52 · Toxic megacolon: A severe colonic complication

Marked colonic dilation in severe colitis

Severe colonic inflammation

Systemic toxicity / emergency

Slide 53 · Perforation is not a routine feature of ulcerative colitis

Deep transmural injury is not the usual pattern of ulcerative colitis.

Perforation is uncommon outside severe cases progressing to toxic megacolon.

The presence of fistulas or penetrating sinus tracts favors Crohn disease.

Acute deterioration warrants assessment for urgent complications.

Slide 54 · Extraintestinal manifestations extend beyond the bowel

System

Examples

Musculoskeletal

Migratory polyarthritis; Sacroiliitis; Ankylosing spondylitis

Ocular

Uveitis

Skin

Inflammatory skin lesions

Hepatobiliary

Primary sclerosing cholangitis

Slide 55 · Primary sclerosing cholangitis: Strong association

Ulcerative colitis

Elevated risk of PSC

Biliary disease may persist

Clinical and surveillance implications

Primary sclerosing cholangitis affects approximately 5% of patients with ulcerative colitis.

Schematic causal framework; Associations should not be interpreted as established single-step mechanisms.

Slide 56 · Ulcerative colitis versus Crohn disease: Gross anatomy

Criterion

Ulcerative colitis

Crohn disease

Distribution

Rectum-based, continuous

Skip lesions frequent

Affected organ

Colon

Any GI segment

Ulcers

Broad and superficial

Often linear / fissuring

Bowel wall

Usually not thickened

Often thickened

Perianal fistula

Not characteristic

May be present

Slide 57 · Ulcerative colitis versus Crohn disease: Microscopy

Criterion

Ulcerative colitis

Crohn disease

Inflammatory depth

Mainly mucosa

Frequently transmural

Crypt abscesses

May occur

May occur

Architectural distortion

May occur

May occur

Noncaseating granulomas

Absent in typical UC

May be found

Fibrosis

Mild / minimal

Can be prominent

Slide 58 · Serology: Supportive association, not a diagnostic definition

Marker

Association in source

Limitation

P-ANCA

Reported in up to 75% of UC

Insufficient to establish diagnosis alone

P-ANCA in Crohn disease

Reported in fewer than 10%

Negative finding does not classify IBD

Anti-Saccharomyces cerevisiae

Often found in Crohn disease

Not a stand-alone diagnostic discriminator

Slide 59 · Diagnosis integrates several independent data streams

Symptoms / duration

Endoscopic distribution

Biopsy morphology

Exclusion of mimics

No isolated histologic sign or serologic marker is universally definitive.

Schematic causal framework; Associations should not be interpreted as established single-step mechanisms.

Slide 60 · Biopsy interpretation: Report activity and chronicity

Assess

Pertinent histologic questions

Activity

Are neutrophils present in crypts, or is there ulceration?

Chronicity

Are glands distorted, lost or metaplastic?

Distribution

Is disease diffuse or patchy across sampled sites?

Alternatives

Are granulomas, infections or other patterns present?

Slide 61 · Pitfalls in differentiating the colitides

Crypt abscesses and distortion occur in both ulcerative colitis and Crohn disease.

Medical treatment and healing can reduce activity or alter the apparent distribution.

Backwash ileitis and the cecal red spot are recognized ulcerative colitis caveats.

Multiple biopsy sites and the clinical pattern are needed for synthesis.

Slide 62 · Indeterminate colitis: A legitimate diagnostic category

Typical ulcerative colitis

Indeterminate colitis

Characteristic continuous colonic disease

Continuous disease may coexist with atypical features

No typical granulomas

Patchy microscopic changes may create ambiguity

No Crohn-type perianal disease

Perianal lesions or Crohn family history may coexist

Confident assignment possible

Cannot confidently assign to UC or Crohn disease

Slide 63 · Differential diagnosis: Not every colitis is IBD

Infectious enterocolitis can cause diarrhea, bleeding and neutrophilic mucosal injury.

Other forms of colitis may produce overlapping architectural or inflammatory patterns.

Morphology alone must be integrated with history, disease distribution and microbiology.

Failure to exclude a treatable infectious cause can misclassify a patient.

Slide 64 · Chronic inflammatory injury can precede neoplasia

Long-standing colonic inflammation

Repeated epithelial damage / regeneration

Dysplasia

Colitis-associated adenocarcinoma

Dysplasia is a recognized precursor; Progression is not inevitable in every patient.

Schematic causal framework; Associations should not be interpreted as established single-step mechanisms.

Slide 65 · Risk of colitis-associated neoplasia varies

Higher-risk feature

Why it matters

Longer disease duration

Risk rises especially after prolonged disease

More extensive colonic involvement

Pancolitis generally confers greater risk

Frequent/severe active inflammation

Cumulative mucosal injury is relevant

Associated primary sclerosing cholangitis

Additional risk and earlier surveillance

Slide 66 · Surveillance targets dysplasia rather than symptoms

Colitis-associated dysplasia may develop in endoscopically inconspicuous flat mucosa.

High-resolution endoscopy and chromoendoscopy can target suspicious areas.

Histologic examination remains essential to establish and grade dysplasia.

Surveillance plans reflect disease duration, extent, inflammation and coexisting PSC.

Slide 67 · Colectomy and the distinction between disease sites

Colectomy removes colon

Colonic UC is eliminated

Extraintestinal disease may remain

Ongoing care can still be required

In contrast to Crohn disease, typical intestinal ulcerative colitis does not recur in another GI segment.

Schematic causal framework; Associations should not be interpreted as established single-step mechanisms.

Slide 68 · Treatment mechanisms correspond to disease biology

Immune cytokine signaling

Anti-inflammatory / biologic therapy

Control mucosal inflammation

Reduced clinical and morphologic activity

Robbins also discusses JAK inhibition and altered lymphocyte trafficking as therapeutic targets.

Schematic causal framework; Associations should not be interpreted as established single-step mechanisms.

Slide 69 · Applied case: A continuous colitis

A young adult has repeated episodes of bloody, mucoid diarrhea. Colonoscopy describes disease extending continuously from the rectum through the left colon. Biopsy shows crypt abscesses and glandular distortion.

Which findings most strongly support ulcerative colitis?

Slide 70 · Case interpretation: Ulcerative colitis is favored

Rectum-based continuous disease is a characteristic distribution.

Crypt abscesses indicate active glandular injury.

Crypt architectural distortion supports chronicity rather than an isolated acute event.

Crypt abscesses are not specific; Clinical and endoscopic context remains essential.

Slide 71 · Applied case: The granuloma problem

A patient with chronic colitis has patchy involvement, a thickened bowel wall, and a well-formed noncaseating granuloma away from a ruptured crypt.

Which alternate inflammatory bowel disease is favored?

Slide 72 · Case interpretation: Crohn disease is favored

Patchiness and bowel-wall thickening contrast with usual ulcerative colitis.

An appropriately situated noncaseating granuloma supports Crohn disease.

Transmural features are more characteristic of Crohn disease.

Classification still depends on the full clinical and pathologic assessment.

Slide 73 · Core discriminators for examination and practice

Domain

Ulcerative colitis clue

Distribution

Continuous colitis beginning in the rectum

Depth

Mucosal-predominant inflammation

Gross

Granularity, broad ulcers, pseudopolyps

Microscopic

Crypt activity plus chronic distortion; No typical granulomas

Complication

Toxic megacolon and colitis-associated neoplasia

Slide 74 · Integrated summary

Ulcerative colitis is a mucosal, rectum-based, continuous form of inflammatory bowel disease.

Complex immune–microbial–epithelial interactions act on a genetically susceptible background.

Activity is marked by neutrophilic crypt injury; Chronicity by distortion, metaplasia and atrophy.

Accurate diagnosis and prognostic assessment require distribution, histology and clinical context.

Slide 75 · References and teaching-source limitations

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th edition (2026), Chapter 17, pp. 727–733.

Morphologic distinctions draw on textbook Table 17.8 and descriptions corresponding to Figs. 17.35, 17.39 and 17.40.

Colitis-associated neoplasia is introduced only as a complication; its dedicated unit provides fuller coverage.

Drawings are original editable schematics; no genuine photomicrographs or textbook figures are reproduced.