NEET MDS Lessons
General Pathology
SMALL INTESTINE
Congenital anomalies
1. Meckel's diverticulum (a true diverticulum) is due to persistence of the omphalomesenteric vitelline duct.
2. Atresia is a congenital absence of a region of bowel, leaving a blind pouch or solid fibrous cord.
3. Stenosis refers to a narrowing of any region of the gastrointestinal tract, which may cause obstruction.
4. Duodenal diverticula are areas of congenital weakness permitting saccular enlargement. The duodenum is the most common region of the small bowel to contain diverticula.
5. Diverticula of jejunum and ileum are herniations of mucosa and submucosa at points where the mesenteric vessels and nerves enter.
Infections
1. Bacterial enterocolitis may be caused by the ingestion of preformed bacterial toxins, producing symptoms ranging from severe but transient nausea, vomiting, and diarrhea (Staphylococcus aureus toxin) to lethal paralysis (Clostridium botulinum toxin). Ingestion of toxigenic bacteria with colonization of the gut (e.g., Vibrio cholera, toxigenic E. coli, various species of Campylobacter jejuni, Shigella, salmonel
Yersinia, and many others) is another potential cause.
2. Nonbacterial gastroenterocolitis
a. Viral
(1) Rotavirus (children)
(2) Parvovirus (adults)
b. Fungal-Candida
c. Parasitic
(1 ) Entamoeba histolytica
(2) Giardia lamblia
3. In HIV patients. Causes of infectious diarrhea in HIV patients include Cryptosporidium, Microsporidia, isospora belli, CMV, and M. avium-intracellulare.
C. Malabsorption is defined as impaired intestinal absorption of dietary constituents.
Clinical features include diarrhea,steatorrhea, weakness, lassitude, and weight loss. Steatorrhea results in deficiency of fat-soluble vitamins (A, D, E, K) and calcium.
1. Celiac sprue
a. Etiology. Celiac sprue (nontropical sprue or gluten enteropathy) is caused by an allergic, immunologic, or toxic reaction to the gliadin component of gluten. There is a genetic predisposition.
Symptoms:
– Steatorrhea, abdominal distention, flatulence, fatigue, and weight loss
Complications:
– Iron and vitamin deficiency
– Risk of lymphoma (T-cell type)
Extraintestinal manifestation:
– Dermatitis herpetiformis (a pruritic papulovesicular rash with IgA deposits at the dermoepidermal junction)
2. Tropical sprue
Etiology. Tropical sprue is of unknown etiology, but may be caused by enterotoxigenic E. coli.
3. Disaccharidase deficiency is due to a deficiency of brush border enzymes. Lactase deficiency is most common.
4. Diverticulosis Coli
- Acquired colonic diverticula are present in nearly half of the population over the age of 50
- Diverticula are associated with low-fiber, low-residue diets
- Etiology is most likely high intraluminal pressure required for propulsion of hard, small stools
- Complications include hemorrhage, acute diverticulitis, perforation, fistula formation
Obstructive lesions
Hernias cause 15% of small intestinal obstruction. They are due to a protrusion of a serosa-lined sac through a weakness in the wall of the peritoneal cavity. They occur most commonly at the inguinal and femoral canals, at the umbilicus, and with scars. They may lead to entrapment, incarceration, and strangulation of the bowel.
Tumors of the small bowel account for only 5% of gastrointestinal tumors.
Benign tumors in descending order of frequency include:
leiomyomas, lipomas, adenomas (polyps), angiomas, and fibromas. Adenomatous polyps are most common in the stomach and duodenum and may be single or multiple, sessile or pedunculated. The larger the polyp, the greater the incidence of malignant transformation.
Malignant tumors, in descending order of frequency, include: endocrine cell tumors, lymphomas, adenocarcinomas, and leiomyosarcomas.
Idiopathic Inflammatory Bowel Disease (IBD)
- Chronic, relapsing, idiopathic inflamamtory disease of the GI tract
Crohn’s Disease
– Transmural granulomatous disease affecting any portion of the GI tract
Ulcerative Colitis
– Superficial, non-granulomatous inflammatory disease restricted to the colon
Ulcerative Colitis
- Bloody mucoid diarrhea, rarely toxic megacolon
- Can begin at any age, peaks at 20-25 years
- Annual incidence of ~10 per 100,000 in US
- Negligible risk of cancer in the first 10 years, but 1% per year risk of cancer thereafter
- Good response to total colectomy if medical therapy fails
Macroscopic
- Normal serosa
- Bowel normal thickness
- Continuous disease
- Confluent mucosal ulceration
- Pseudopolyp formation
Microscopic
- Crypt distortion + shortening
- Paneth cell metaplasia
- Diffuse mucosal inflammation
- Crypt abscesses
- Mucin depletion
- Mucosal ulceration
Crohn’s Disease
- Variable and elusive clinical presentation with diarrhea, pain, weight loss, anorexia, fever
- Can begin at any age, peaks at 15-25 years
- Annual incidence of ~3 per 100,000 in US
- Many GI complications and extracolonic manifestations
- Risk of cancer less than in UC
- Poor response to surgery
Macroscopic
Fat wrapping
Thickened bowel wall
Skip Lesions
Stricture formation
Cobblestoned mucosa
Ulceration
Microscopic
- Cryptitis and crypt abscesses
- Transmural inflammation
- Lymphoid aggregates +/- granulomas
- “Crohn’s rosary”
- Fissuring
- Neuromuscular hyperplasia
DYSPLASIA
It is disturbed growth or cells in regard to their size, shape arrangement. In its mild degrees it represents a reversible reaction to chronic inflammation whereas the most severe degrees warrant a labelling of intraepithelial neoplasia. Hence it includes a wide spectrum of changes ranging from a reversible disorientation to 'carcinoma-in-situ'.
Histologically it is characterized by:
o Basal cell hyperplasia.
o Variation in size and shape of cells.
o Disorderly maturation.
o Increased mitotic activity.
o Disorientation of arrangement of cells (loss of polarity)
Dysplasia is commonly seen in:
o Squamous epithelium of cervix.
o Bronchial epithelium in habitual smokers.
o Gastric and colonic mucosa in long standing inflammation
o Oral and vulval leucoplakia
Post viral (post hepatitic) cirrhosis (15-20%)
Cause:- Viral hepatitis (mostly HBV or HCV)
Acute hepatitis → chronic hepatitis → cirrhosis.
Pathology
Liver is shrunken. Fatty change is absent (except with HCV). Cirrhosis is mixed.
M/E :-
Hepatocytes-show degeneration, necrosis as other types of cirrhosis.
Fibrous septa -They are thick and immature (more cellular and vascular).
- Irregular margins (piece meal necrosis).
- Heavy lymphocytic infiltrate.
Prognosis:- - More rapid course than alcoholic cirrhosis.Hepatocellular carcinoma is more liable to occur
Rocky Mountain Spotted Fever (Spotted Fever; Tick Fever; Tick Typhus)
An acute febrile disease caused by Rickettsia rickettsii and transmitted by ixodid ticks, producing high fever, cough, and rash.
Symptoms and Signs
The incubation period averages 7 days but varies from 3 to 12 days; the shorter the incubation period, the more severe the infection. Onset is abrupt, with severe headache, chills, prostration, and muscular pains. Fever reaches 39.5 or 40° C (103 or 104° F) within several days and remains high (for 15 to 20 days in severe cases),
Between the 1st and 6th day of fever, most patients develop a rash on the wrists, ankles, palms, soles, and forearms that rapidly extends to the neck, face, axilla, buttocks, and trunk. Often, a warm water or alcohol compress brings out the rash. Initially macular and pink, it becomes maculopapular and darker. In about 4 days, the lesions become petechial and may coalesce to form large hemorrhagic areas that later ulcerate
Neurologic symptoms include headache, restlessness, insomnia, delirium, and coma, all indicative of encephalitis. Hypotension develops in severe cases. Hepatomegaly may be present, but jaundice is infrequent. Localized pneumonitis may occur. Untreated patients may develop pneumonia, tissue necrosis, and circulatory failure, with such sequelae as brain and heart damage. Cardiac arrest with sudden death occasionally occurs in fulminant cases.
Wuchereria bancrofti, Brugia malayi (Filariasis)
- the microfilaria of Wuchereria bancrofti or Brugia malayi (nematodes) are transmitted to man by the bite of infected mosquitoes (Anophele, Aedes, Culex).
- microfilaria characteristically circulate in the bloodstream at night and enter into the lymphatics, where they mature and produce an inflammatory reaction resulting in lymphedema (elephantiasis) of the legs, scrotum, etc.
Parkinson’s disease
a. Characterized by the degeneration of neurons in the basal ganglia, specifically the substantia nigra and striatum.
b. Histologic findings in affected neurons include Lewy bodies.
c. Clinically, the disease affects involuntary and voluntary movements. Tremors are common. Symptoms include pin-rolling tremors, slowness of movements, muscular rigidity, and shuffling gait.
Autopsy
Autopsy is examination of the dead body to identify the cause of death. This can be for forensic or clinical purposes.