Sigmoid Diverticular Disease

Slide 1 · Sigmoid Diverticular Disease

Mechanisms • Morphology • Clinicopathologic consequences

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Distinguish an acquired colonic pseudodiverticulum from a true diverticulum.

Explain why the sigmoid colon is vulnerable to diverticular formation.

Recognize gross and microscopic architecture.

Relate diverticulosis to symptoms, diverticulitis, and serious complications.

Slide 3 · The clinical spectrum begins with an outpouching

Acquired colonic mucosal outpouching

Diverticulosis: Diverticula are present

Some people develop bowel symptoms

Diverticulitis if a diverticulum inflames

Presence of diverticula does not itself establish diverticulitis.

Slide 4 · A colonic diverticulum is a pseudodiverticulum

Colonic lumen

Muscularis propria

Mucosal sac beyond muscle

Schematic; Not histologic evidence

Slide 5 · True versus acquired pseudodiverticula

True diverticulum

Includes all bowel-wall layers

Congenital example: Meckel diverticulum

Not the typical lesion of sigmoid diverticular disease

Colonic pseudodiverticulum

Acquired lesion

Mucosa and submucosa protrude beyond muscularis propria

Does not include a complete muscular wall

Slide 6 · Colonic diverticula are acquired lesions

Pre-existing focal site of reduced muscle support

Elevated colonic intraluminal pressure

Mucosa and submucosa are displaced outward

Pseudodiverticular sac is formed

The sac forms at a point of weakness rather than by duplication of every wall layer.

Slide 7 · Age strongly shapes prevalence

≈50%

Prevalence approaches this value

Western adults older than 60 years

Diverticula are rare in people younger than 30 years. The estimate is population-specific, not a global prevalence.

Slide 8 · Epidemiology varies across populations

Western populations

Common in older adulthood

Sigmoid involvement is typical

Lower stool bulk from low-fiber diets is implicated

Japan and under-resourced settings

Diverticulosis described as less common

Dietary differences are proposed

The source does not establish a single proven explanation

Slide 9 · The sigmoid colon is a characteristic site

Reduced stool bulk

Exaggerated peristaltic contractions

Increased intraluminal pressure in sigmoid

Herniation through weak muscular sites

The site of greatest mechanical load overlaps focal structural weak points.

Slide 10 · Regional patterns are not identical

Population context

Predominant location described

Interpretive caution

Western populations

Sigmoid colon

Described tendency, not an absolute rule

Asian and African populations

Right colon

Distribution varies by population

Slide 11 · The bowel wall has organized supporting layers

Luminal side

Mucosa

Submucosa

Inner circular muscle

Outer longitudinal muscle / taeniae

Pericolic tissue

Schematic — wall-layer relationships

Slide 12 · Two muscular layers have different orientations

Inner circular muscle

Surrounds the lumen

Contains penetrations by vessels and nerves

May undergo hypertrophy in diverticulosis

Outer longitudinal muscle

Continuous coverage reinforces small intestine

In the colon, longitudinal muscle forms taeniae coli

Leaves some penetrating sites without reinforcement

Slide 13 · Taeniae coli create discontinuous reinforcement

Longitudinal colon muscle concentrated into three bands

Intervening colon wall has less outer muscle support

Penetrating sites in the inner layer remain vulnerable

The outer longitudinal muscle distribution is central to colonic susceptibility.

Slide 14 · Vasa recta and nerves identify weak points

Luminal side

Mucosa

Submucosa

Inner circular muscle

Outer longitudinal muscle / taeniae

Pericolic tissue

Focal muscle discontinuity

Schematic — wall-layer relationships

Slide 15 · The small intestine has an anatomical advantage

Small intestine

Discontinuities occur at penetration sites

An outer continuous longitudinal muscle layer reinforces these gaps

Less exposed structural weakness at these sites

Colon

Longitudinal muscle is gathered into taeniae coli

Penetrating sites may lack outer reinforcement

Elevated pressure can force mucosa outward

Slide 16 · Intraluminal pressure is the immediate mechanical force

Elevated luminal pressure

Load on an unsupported wall region

Mucosal and submucosal protrusion

Flask-like external sac

Pressure alone is an incomplete explanation without anatomy.

Slide 17 · Low-fiber diets act through stool bulk

Low-fiber dietary pattern

Reduced stool bulk

Exaggerated sigmoid contraction

Increased focal luminal pressure

This is the proposed pathogenic pathway; It does not prove fiber prevents diverticulitis.

Slide 18 · Sigmoid motility amplifies mechanical stress

Peristaltic contraction

A contractile event raises localized mechanical forces within the sigmoid segment.

Pressure-bearing wall

Focal unreinforced sites respond differently from muscle-supported wall.

Structural consequence

Repeated force can favor mucosal herniation at penetrations.

Slide 19 · A two-factor mechanism explains diverticular formation

Predisposing architecture

Nerve and vessel penetration of circular muscle

Limited outer longitudinal reinforcement

Localized discontinuities

Driving forces

Elevated intraluminal pressure

Exaggerated sigmoid contractions

Reduced stool bulk as a contributing context

Neither the weak spot nor the pressure explains the lesion as clearly in isolation.

Slide 20 · Explain sigmoid predominance from first principles

Taeniae-related weak sites

High-pressure sigmoid contraction

Outward mucosal herniation

Numerous sigmoid pseudodiverticula

This mechanism accounts for the characteristic Western pattern.

Slide 21 · Gross diverticula are small flask-shaped sacs

0.5–1 cm

Typical described diameter

Gross morphology

The flask-like configuration has a relatively narrow opening and an outward-expanded sac. This is a morphology description, not a clinical size threshold.

Slide 22 · Diverticula may appear evenly spaced

Observed pattern

Multiple flask-like outpouchings can be distributed at relatively regular intervals.

Anatomic explanation

Penetrating nerves and arteries recur in an organized pattern along the colonic wall.

Clinicopathologic meaning

Distribution reflects wall architecture rather than random erosions.

Slide 23 · The diverticular neck and sac are mechanically distinct

Colonic lumen

Muscularis propria

Mucosal sac beyond muscle

Schematic; Not histologic evidence

Slide 24 · Mucosa forms the lining of the diverticular wall

Colonic lumen

Muscularis propria

Mucosal sac beyond muscle

Schematic; Not histologic evidence

Slide 25 · The muscularis propria is not a complete sac wall

Colonic lumen

Muscularis propria

Mucosal sac beyond muscle

Schematic; Not histologic evidence

Slide 26 · Little tissue may separate mucosa from serosa

Thin diverticular wall

Subserosal adipose tissue immediately external

Inflammatory spread can reach serosal surface

Serositis or more extensive extension

Slide 27 · Circular muscle hypertrophy often accompanies disease

Luminal side

Mucosa

Submucosa

Inner circular muscle

Outer longitudinal muscle / taeniae

Pericolic tissue

Thickened inner circular layer

Schematic — wall-layer relationships

Slide 28 · Gross inspection: Stool-filled diverticular sacs

Luminal appearance

Diverticula may contain stool and occur in a regularly spaced arrangement.

Cross section

Mucosa is seen protruding through the muscularis propria.

Interpretive limit

This slide illustrates reported features; It is not a reproduced textbook specimen.

Slide 29 · A cross section explains the pseudodiverticulum

Colonic lumen

Muscularis propria

Mucosal sac beyond muscle

Schematic; Not histologic evidence

Slide 30 · Microscopic recognition relies on wall-layer relationships

Identify mucosa extending beyond the expected contour of the muscularis propria.

Look for an interruption or severe attenuation of the intervening muscular wall.

Recognize that a thin pericolic soft-tissue interface may lie beyond the sac.

Do not label this schematic as authentic H&E morphology.

Slide 31 · Diverticulosis and diverticulitis are different states

Diverticulosis

One or more acquired diverticula are present

Many affected individuals have no symptoms

Inflammation is not implied by this term

Diverticulitis

Inflammation develops within a diverticulum

Obstruction of the diverticular orifice is a possible trigger

Inflammation may extend to surrounding tissues

Slide 32 · Orifice obstruction may initiate diverticulitis

Existing diverticular sac

Possible obstruction at sac orifice

Inflammation develops within diverticulum

Local or spreading diverticulitis

Obstruction as a possible cause, not a necessary event in every case.

Slide 33 · Diverticular inflammation can reach the serosa

Inflammation in mucosal sac

Little intervening tissue outside sac

Extension to serosal surface

Serositis

Slide 34 · Mucosal injury can progress to perforation

Mucosal injury in thin-walled diverticulum

Failure of the local tissue barrier

Perforation through the wall

Risk of extraintestinal contamination

Perforation represents a severe complication, not the usual course of all diverticulosis.

Slide 35 · A pericolonic abscess is a localized complication

Inflammation or mucosal injury

Extension beyond the diverticular wall

Localized pericolonic collection

Pericolonic abscess

Slide 36 · Sinus tracts arise from extension beyond the bowel

Inflamed thin-walled diverticulum

Local injury extends past normal wall

Abnormal tract in adjacent tissues

Sinus tract formation

Slide 37 · Peritonitis indicates extensive inflammatory spread

Severe diverticular injury

Perforation and outward spread

Peritoneal inflammatory response

Peritonitis

Potential for peritonitis gives thin-walled diverticula important clinical significance.

Slide 38 · Complications follow tissue-boundary failure

Serositis

Inflammation reaches the outer serosal surface.

Perforation

The damaged diverticular wall is breached.

Pericolonic abscess

Localized inflammation forms an abscess next to the colon.

Sinus tracts / peritonitis

Spread may create abnormal tracts or involve the peritoneum.

Slide 39 · Most people with diverticula remain asymptomatic

Most affected people

Remain asymptomatic throughout life; A diverticulum itself need not produce complaints.

Symptomatic subset

Manifestations in about one-fifth of affected individuals.

Inflamed subset

Only a minority develop diverticulitis; Severe complications are not the default.

Slide 40 · About one-fifth develop manifestations

≈20%

Develop clinical manifestations

Denominator: Individuals with diverticular disease

The estimate describes symptoms such as pain, discomfort, altered bowel habits and distention. It is not the proportion who develop diverticulitis.

Slide 41 · Pain may be episodic or persistent

Intermittent symptoms

Intermittent cramping

Symptoms may vary over time

An anatomical lesion can coexist with fluctuating discomfort

Persistent symptoms

Continuous lower abdominal discomfort

Symptoms do not necessarily prove acute inflammation

Assess the entire clinical pattern rather than pain alone

Slide 42 · Bowel-habit symptoms may predominate

Constipation

A recognized manifestation of symptomatic diverticular disease.

Abdominal distention

May be present with lower abdominal discomfort.

Incomplete evacuation

A sensation of never fully emptying the rectum may occur.

Slide 43 · Alternating bowel habits can mimic IBS

Symptomatic diverticular disease

Known acquired colonic outpouchings

Constipation may alternate with diarrhea

Cramping or distention may coexist

IBS-like clinical pattern

Alternating constipation and diarrhea

Symptom overlap alone is not definitive

The source explicitly notes mimicry of IBS

Slide 44 · Symptoms do not equal inflammation

Diverticula may be asymptomatic

Some produce pain or altered bowel habit

Diverticulitis specifically implies inflammation

Distinguish the anatomical condition, symptomatic disease, and inflamed disease.

Slide 45 · Fiber and prevention require careful wording

Proposed pathogenesis

Low dietary fiber may reduce stool bulk

Smaller bulk may accompany exaggerated contraction

Mechanistic plausibility supports a hypothesis

Prevention remains uncertain

Robbins does not establish that high fiber prevents diverticulitis

A proposed risk mechanism is not proof of prevention

Avoid translating this into a quantitative effect

Slide 46 · Fiber supplementation may alleviate symptoms

Dietary fiber supplementation

Possible improvement in bowel-related symptoms

No established prevention claim in the supplied text

Symptomatic benefit and protection from diverticulitis are separate questions.

Slide 47 · Many episodes of diverticulitis resolve without surgery

Diverticulitis most often resolves spontaneously.

This statement does not imply that every inflammatory episode is harmless.

Severe disease can cause perforation and extraintestinal inflammation.

Course and risk depend on the clinical episode; No invented intervention algorithm is shown.

Slide 48 · Surgery is generally reserved for selected cases

Typical diverticulitis course

Most episodes resolve spontaneously

Not every attack requires surgery

Avoid treating uncomplicated anatomy as a surgical indication

When surgery is considered

Severe diverticulitis

Recurrent diverticulitis

Specific operative thresholds are outside this textbook excerpt

Slide 49 · Morphology predicts clinically important complications

Morphologic finding

Mechanistic implication

Possible consequence

Thin diverticular wall

Little separation from serosa

Serositis

Mucosal damage

Wall integrity can fail

Perforation

Pericolic extension

Spread beyond colon

Abscess or sinus tract

Peritoneal spread

Extensive inflammation

Peritonitis

Slide 50 · The disease can be reconstructed as a causal chain

Focal wall weakness + increased pressure

Mucosal / submucosal outpouching

Often asymptomatic diverticulosis

Inflammation can lead to complications

Anatomical diverticula precede diverticulitis; Inflammatory complications are conditional.

Slide 51 · Applied case: Incidentally identified diverticula

Clinical vignette

An older adult is found to have multiple sigmoid diverticula.

There has been no abdominal discomfort or change in bowel habits.

No inflammatory findings are described.

Interpretation task

What is established from the vignette?

Diverticulosis; Not diverticulitis.

Slide 52 · Applied case: Fluctuating bowel symptoms

Clinical vignette

A patient with known sigmoid diverticula reports intermittent cramping.

Constipation alternates with diarrhea.

No evidence of diverticular inflammation is provided.

Interpretation task

Can these symptoms alone establish diverticulitis?

No. The source notes an IBS-like mimic.

Slide 53 · Applied case: Pericolic inflammatory extension

Clinical vignette

A diverticulum becomes inflamed.

Inflammation extends beyond its thin outer wall.

A localized pericolonic abscess develops.

Interpretation task

Why can spread occur relatively easily?

There is little tissue between sac mucosa and serosa.

Slide 54 · Morphologic interpretation: A low-power schematic

Colonic lumen

Muscularis propria

Mucosal sac beyond muscle

Schematic; Not histologic evidence

Slide 55 · Differentiate a polyp from a diverticulum

Diverticulum

Outpouching from the normal colonic wall

Mucosa and submucosa extend outward through muscle

A lesion of wall contour and support

Intestinal polyp

Raised mucosal lesion extending toward the lumen

May be sessile or pedunculated

A distinct morphologic concept from an external sac

Slide 56 · Clinicopathologic synthesis: Five discriminators

Acquired pseudodiverticulum: Mucosa and submucosa without a complete muscular wall.

Focal penetrating neurovascular sites + elevated pressure explain formation.

The sigmoid is especially involved in Western populations.

Thin-walled sacs permit serositis, perforation, abscesses, sinus tracts, or peritonitis.

Most patients are asymptomatic; Inflammation defines diverticulitis.

Slide 57 · References and source scope

Robbins, Cotran & Kumar: Pathologic Basis of Disease

11th edition (2026), Chapter 17: The Gastrointestinal Tract

“Sigmoid Diverticular Disease,” printed pages 734–735

Scope and figure provenance

Content follows the supplied topic extraction and adjacent heading.

Original textbook Fig. 17.43 was not reproduced; diagrams are original schematic, native PowerPoint objects.