Macroscopic picture and mechanism of formation
Diverticular disease is a complex pathology which, from a morphological standpoint, is characterized by the appearance of multiple pathological protrusions. These formations can be localized in absolutely any part of the digestive tract, disrupting its normal anatomical structure.
A key feature and the main distinguishing sign of this disease is the formation of so-called false diverticula. To understand the essence of the pathology, it is necessary to clearly draw the line between true and false formations. A true diverticulum, which is most often congenital in origin, is a full-fledged protrusion of the entire bowel wall, including absolutely all of its layers. In contrast, a false diverticulum is a hernia-like protrusion exclusively of the mucous membrane.
Macroscopically, this process looks like the formation of a peculiar blind "pouch". This pouch aggressively prolapses, protruding beyond the muscular layer of the bowel wall. Very often in gross specimens, one can observe how these mucosal hernias penetrate deep into the surrounding tissues, invading directly into the tissue of the appendices epiploicae of the intestine.
Anatomic landmarks of the intestinal wall
For accurate histological verification of the disease, a pathologist needs to navigate the microscopic anatomy of the intestinal wall. The pathological process of herniation affects strictly defined layers, disrupting their normal relationship.
Classical histology distinguishes the following layers that figure in the morphogenesis of a diverticulum:
- Lamina propria (proper plate of the mucous membrane) is the connective tissue framework which serves as the main arena for the development of inflammatory reactions in the complicated course of the disease.
- Lamina muscularis mucosae (muscular plate of the mucous membrane) is the thinnest layer of smooth muscle cells serving as a boundary between the mucosa and underlying tissues.
- Submucosa (submucosal base) is the layer providing mobility to the mucous membrane.
- Tunica muscularis (muscular layer) is a robust muscular framework of the intestine. It is precisely through defects in the tunica muscularis that the mucosa herniates outward, forming the morphological substrate of a false diverticulum.
Histological changes in inflammation
When an inflammatory process joins the structural deformation of the wall, the microscopic picture of the biopsy specimen undergoes very characteristic changes. The main morphological blow in this case is taken by the lamina propria.
A detailed microscopic examination reveals the following triad of signs:
- Specific cellular infiltration. A dense inflammatory infiltrate forms in the lamina propria of the mucous membrane. Its cellular composition is dominated by plasma cells (a plasmacytic infiltrate forms). The most important diagnostic nuance is the obligatory admixture of eosinophils in this pool of cells.
- Lymphoid hyperplasia. In response to the pathological process in the tissues of the altered bowel wall, lymphoid follicles begin to actively form, serving as a striking marker of the strain on local tissue immunity.
- Destruction of the epithelial lining. Surface defects—erosions—form on the surface of the mucous membrane. These erosive injuries are not punctiform; they are quite extensive and involve several adjacent intestinal crypts at once, leading to a disruption of the normal architectonics of the glandular apparatus.
Briefly: answers to topical questions
In which section of the large intestine are acquired diverticula most frequently localized?
Acquired diverticula are most frequently localized in the left colon. In the "Western" type of the disease, up to 95% of protrusions are detected in the sigmoid colon, with their number decreasing in the proximal direction. Segmental involvement affecting only the sigmoid and transverse colon is also possible. In the "Eastern" type, which is much less common, diverticula are localized in the cecum and ascending colon.
What macroscopic complications of diverticular disease are distinguished in pathological anatomy?
According to the cited sources, macroscopic complications of diverticular disease include inflammatory complications, fistulas, hemorrhages, and rare complications. The following pathologies are distinguished:
- Fistulas (fistula) — most commonly involving the urinary bladder with the formation of a colovesical fistula.
- Giant cyst (giant cyst) — a rare complication; it is a pseudocyst formed upon the expansion of a walled-off subserosal perforation.
- Abscess — pericolic, pelvic, intra-abdominal, retroperitoneal, or diverticular.
- Peritonitis — generalized purulent or fecal.
- Infiltrate — acute or chronic paraintestinal; pericolic infiltrate is also described.
- Stenosis.
- Hemorrhage — acute or recurrent.
- Pericolic phlegmon.
- Diverticular perforation.
- Volvulus (volvulus) as a rare complication.
What pathogenetic factors lead to increased intraluminal pressure and the formation of diverticula?
The formation of diverticula is caused by structural changes in the bowel wall, but there is no direct data on the factors increasing intraluminal pressure in the sources. The pathogenesis includes the following stages:
- Deposition of elastin in the taeniae, which causes contraction and shortening of the bowel.
- Corrugation (corrugation) of the mucous membrane and circular muscle layers.
- Formation of a thickened bowel with interdigitating folds (interdigitating folds).
Diverticula themselves form in anatomical "points of weakness"—places where vasa recta penetrate through the circular muscle layer.
With which diseases is it necessary to perform macroscopic differential diagnosis of diverticular disease?
According to the cited sources, the following areas of differential diagnosis are indicated for diverticular disease and its complications:
- Cancer / tumor lesion of the large intestine — CT perfusion parameters may play a role in the differential diagnosis between cancer and diverticulitis.
- Duplication cyst (duplication cyst) — differential diagnosis in a giant cyst associated with diverticular disease.
- Ulcerative colitis — the source indicates that ulcerative colitis must be differentiated from diverticulitis and other diseases.
To easily remember the difference between a false and a true diverticulum, use the association: "A lie is always superficial." A false diverticulum consists only of the superficial layer (mucous membrane), which "escapes" through the muscular layer, much like a hernia.
Class and exam questions
What is the main morphological difference between a false and a true diverticulum?
A true (congenital) diverticulum contains all layers of the intestinal wall. A false diverticulum represents a hernia-like protrusion exclusively of the mucous membrane beyond the muscular layer.
Which cells predominate in the inflammatory infiltrate in this pathology?
In the proper plate of the mucous membrane (lamina propria), a predominantly plasmacytic infiltrate is observed with a characteristic and diagnostically important admixture of eosinophils.
How does the glandular apparatus of the intestine change during diverticular inflammation?
Extensive erosions form on the mucous membrane, which capture and destroy several intestinal crypts at once. The formation of lymphoid follicles is also observed in the tissues.
Where does the mucosa most commonly herniate during the formation of a «pocket»?
The mucous membrane protrudes beyond the tunica muscularis, very often penetrating directly into the tissue of the appendices epiploicae of the intestine.
What else to study on this topic
- Pathogenesis of the hernia-like protrusion of the mucous membrane through the tunica muscularis.
- Morphological differences between congenital (true) and acquired (false) diverticula.
- The role of eosinophils and plasmacytes in the inflammatory infiltrate of the lamina propria.
- The mechanism of erosion formation and destruction of intestinal crypts during inflammation.
- Topography of the appendices epiploicae and their involvement in diverticular disease.
Master the entire topic in the "Pathological Anatomy" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Diverticular disease of the intestine" and 4,414 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 153 video lessons on the subject
Other topics in the «Digestive System Diseases» section
Free video lessons: pathological anatomyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.