Diverticular Disease

Etiology and Risk Factors

Segmental contraction, local pressure gradients, wall remodeling, genetic susceptibility, and age-related changes contribute to formation, often in the sigmoid colon (Mills & Ciorba, 2019; Peery et al., 2026; Rej et al., 2023).

Epidemiology and Clinical Context

Population context: Diverticulosis becomes more common with age, but acute diverticulitis is not limited to older adults. Immunosuppression, medical frailty and substantial comorbidity increase management risk and favor antibiotics and closer monitoring; imaging findings, clinical stability and access to reassessment guide disposition (Peery et al., 2026; Rej et al., 2023).

Pathophysiology

Colon wall mechanics and diverticulum formation

The vasa recta penetrate the circular muscle layer where mucosa and submucosa can herniate. Segmental contraction, local pressure gradients, wall remodeling, genetic susceptibility, and age-related changes contribute to formation, often in the sigmoid colon. Dietary patterns and genetic susceptibility influence risk, but constipation is no longer presumed to cause diverticulosis or diverticulitis. An acquired colonic diverticulum lacks muscularis propria in its sac, whereas a true congenital Meckel diverticulum contains all bowel-wall layers (Mills & Ciorba, 2019; Peery et al., 2026; Rej et al., 2023).

From uncomplicated inflammation to complicated disease

• Localized colonic wall inflammation causes focal tenderness and reactive pericolic changes; CT may show segmental wall thickening and fat stranding.
• Microperforation may remain contained, creating localized phlegmon or pericolic abscess. More extensive disruption may produce free perforation and diffuse peritonitis.
• Repeated or persistent injury can create fibrosis, stricture, and bowel obstruction. A tract to the bladder, vagina, or another organ may develop, producing a fistula.

A history of pneumaturia, fecaluria, or repeated polymicrobial urinary tract infection should prompt evaluation for colovesical fistula. Persistent vomiting, distension, and inability to pass stool or flatus suggest obstruction. Generalized rigidity or hemodynamic instability raises concern for perforation and sepsis (Norris, 2020; Rej et al., 2023).

Clinical Manifestations

Three clinically different states

State	Mechanism	Presentation and clinical implication
Diverticulosis	Outpouchings exist without active inflammation.	Usually incidental and asymptomatic; the finding alone does not establish the cause of chronic abdominal pain.
Diverticulitis	Segmental mural and pericolic inflammation may follow focal injury and microperforation.	Persistent focal pain, commonly left lower quadrant, sometimes fever and leukocytosis; complications include abscess and perforation.
Diverticular hemorrhage	Vasa recta adjacent to a diverticulum erode or rupture.	Often sudden, painless hematochezia; potentially substantial bleeding without diverticulitis.

Pathophysiologic distinction: Fever and localized tenderness suggest an inflammatory complication, whereas acute painless hematochezia directs evaluation toward a bleeding lesion. Their coexistence is possible, but one should not be used as a synonym for the other.

Diagnostic Evaluation

• Stable patient with suspected first diverticulitis episode: obtain focused history, abdominal examination, pregnancy assessment when relevant, and indicated CBC/chemistry and inflammatory markers. Cross-sectional CT abdomen/pelvis can establish diagnosis, assess alternative causes, and identify abscess or perforation.
• Suspected complicated diverticulitis or high-risk patient: assess volume status, organ dysfunction, peritoneal signs, leukocytosis, immunocompromise, obstruction, and inability to tolerate oral intake. CT helps characterize source control needs; urgent surgical evaluation is warranted for peritonitis or unstable physiology.
• Active acute lower GI bleeding: assess hemodynamics, orthostasis, medications (including antithrombotics/NSAIDs), blood count, resuscitation needs, and appropriate localization tests. Diverticulosis on historical imaging does not prove the bleeding source; angiodysplasia, ischemia, neoplasm, and other etiologies remain possible.
• Avoid routine diagnostic colonoscopy during active acute diverticulitis when inflammation makes the colon vulnerable. After recovery, the 2026 ACG guideline recommends colonoscopy after complicated diverticulitis to exclude malignancy; after uncomplicated disease, it is suggested for patients with alarm features or who are not up to date with colorectal cancer screening. Defer colonoscopy until the acute inflammation has resolved, generally at least 6–8 weeks after the episode, and consider prior colonoscopy quality and timing in planning follow-up (Peery et al., 2026).

CT findings and host risk define the branch

Uncomplicated diverticulitis typically shows localized mural thickening and pericolic inflammatory fat change without an abscess, perforation, stricture or fistula. A pericolic or pelvic abscess, free air with peritonitis, fistula or mechanical obstruction denotes complicated disease and changes disposition and source-control needs. Leukocytosis, fever and left-lower-quadrant pain are supportive but not independently specific; CT also helps exclude alternative diagnoses, particularly in older adults or atypical presentations (Mills & Ciorba, 2019; Peery et al., 2026; Rej et al., 2023).

Expected Findings

Uncomplicated diverticulitis typically shows localized mural thickening and pericolic inflammatory fat change without an abscess, perforation, stricture or fistula (Mills & Ciorba, 2019; Peery et al., 2026; Rej et al., 2023).

Differential Diagnosis

Diverticulosis on historical imaging does not prove the bleeding source; angiodysplasia, ischemia, neoplasm, and other etiologies remain possible.

Diagnostic Limitations and Reassessment

Leukocytosis, fever and left-lower-quadrant pain are supportive but not independently specific; CT also helps exclude alternative diagnoses, particularly in older adults or atypical presentations (Mills & Ciorba, 2019; Peery et al., 2026; Rej et al., 2023).

Treatment and Management

Incidental, asymptomatic diverticulosis generally does not require drugs or surgery. Lifestyle measures may help bowel health, but there is no reason to routinely avoid nuts, seeds, corn, or popcorn solely because diverticula are present (Peery et al., 2026).

The 2026 ACG guideline supports managing selected patients with uncomplicated diverticulitis without routine antibiotics when they are immunocompetent, not medically frail, have no recent antibiotic exposure, are hemodynamically stable and able to tolerate oral intake, and have neither systemic inflammatory features nor high-risk imaging findings, with reliable outpatient follow-up and adequate support. Immunosuppression, frailty, substantial comorbidity, clinical deterioration, or poor access to reassessment favor antibiotics and closer monitoring. Use CT to confirm a first episode and identify complications before applying a low-risk outpatient pathway (Peery et al., 2026).

Complicated disease requires management of sepsis, fluids and electrolytes, analgesia, and adequate source control when indicated. Percutaneous abscess drainage or operative intervention may be necessary. Surgical decisions after recovery depend on individual recurrence burden, complication phenotype and patient risk rather than a fixed number of attacks (Peery et al., 2026; Rej et al., 2023).

Antibiotic decisions and postepisode evaluation

Observation without routine antibiotics is reasonable only for selected immunocompetent patients with clearly uncomplicated, mild disease, no recent antibiotic exposure, and reliable follow-up, as described above. Systemic illness, frailty, significant comorbidity, immunosuppression or complicated imaging findings favor antibiotics and closer monitoring. Abscess drainage or surgery depends on source-control needs, clinical severity and procedural feasibility. Colon evaluation after recovery follows the complicated versus uncomplicated, alarm-feature, and screening-status distinctions above (Peery et al., 2026).

Complications and Red Flags

Complication triage and key differential

Finding	Alternative or complication	Why it changes management
Focal lower abdominal pain with fever	Diverticulitis, appendicitis, ischemic or infectious colitis, gynecologic/urinary disease.	Clinical localization alone cannot reliably establish diagnosis.
Abscess on CT	Contained perforation.	May require antibiotics and percutaneous drainage or surgery according to clinical severity, source-control needs and procedural feasibility.
Pneumaturia / recurrent urinary infection	Colovesical fistula.	Requires targeted imaging and colorectal/urologic evaluation.
Rigid abdomen, free intraperitoneal air, shock	Free perforation and peritonitis.	Immediate resuscitation and emergency surgical assessment.
Abrupt painless hematochezia	Diverticular hemorrhage, angiodysplasia and other lower GI bleeding.	Resuscitation and bleeding-source localization take priority.

Clinical Reasoning Priorities

A patient has two days of focal left lower quadrant pain and fever, with CT showing sigmoid fat stranding and a 4-cm adjacent fluid collection. This is not uncomplicated diverticulitis: the collection suggests localized perforation with an abscess. Assess stability and sepsis, initiate appropriate antimicrobial and supportive care, and obtain source-control input. In contrast, an afebrile patient with sudden painless hematochezia requires bleeding evaluation even if diverticula are known to be present.

---

---

References

Mills, J. C., & Ciorba, M. A. (2019). Gastrointestinal disease. In G. D. Hammer & S. J. McPhee (Eds.), Pathophysiology of disease: An introduction to clinical medicine (8th ed., Chapter 13). McGraw-Hill Education.

Norris, T. L. (2020). Porth’s essentials of pathophysiology (5th ed.). Wolters Kluwer.

Peery, A. F., Strate, L. L., Stollman, N., Mankaney, G., Chang, J. W., & Grover, S. (2026). ACG clinical guideline: Colonic diverticulitis. American Journal of Gastroenterology, 121(7), 1549–1561. https://doi.org/10.14309/ajg.0000000000004047

Rej, A., Chew, T. S., & Sanders, D. S. (2023). Gastroenterology. In I. D. Penman, S. H. Ralston, M. W. J. Strachan, & R. P. Hobson (Eds.), Davidson’s principles and practice of medicine (24th ed., pp. 781–858). Elsevier.