NEET MDS Lessons
General Pathology
Pheochromocytoma
Pheochromocytomas are neoplasms composed of chromaffin cells, which as their normal counterparts synthesize and release catecholamines.
1. Arise in association with one of several familial syndromes such as MEN syndromes, type 1 neurofibromatosis, von Hippel-Lindau disease, and Sturge-Weber syndrome.
2. Are extra-adrenal, occurring in sites such as the organ of Zuckerkandl and the carotid body, where they are usually called paragangliomas rather than pheochromocytomas.
3. Are bilateral; but in association with familial syndromes, this figure may rise to 50%.
4. Are malignant; frank malignancy, however, is more common in extra-adrenal tumors.
Gross features
- The size of these tumors is quite variable ranging from small to huge masses.
- Sectioning shows yellow-tan, well-defined tumor that compress the adjacent adrenal. Large lesions display areas of hemorrhage, necrosis, and cystic degeneration.
- Incubation of the fresh tissue with potassium dichromate solutions converts the tumor a dark brown color.
Microscopic features
- These tumors are composed of polygonal to spindle-shaped chromaffin cells and their supporting sustentacular cells, arranged in well-defined small nests (Zellballen)," rimmed by a rich vascular network.
- The cytoplasm is often finely granular (catecholamine-containing granules)
- The nuclei are often quite pleomorphic.
- Both capsular and vascular invasion may be encountered in benign lesions, and the presence of mitotic figures per se does not imply malignancy. Therefore, the definitive diagnosis of malignancy in pheochromocytomas is based exclusively on the presence of metastases. These may involve regional lymph nodes as well as more distant sites, including liver, lung, and bone.
The laboratory diagnosis of pheochromocytoma is based on demonstration of increased urinary excretion of free catecholamines and their metabolites, such as vanillylmandelic acid (VMA)& metanephrines.
Growth and spread of tumours
Growth in excess of normal is a feature of all tumours but extension to tissue away from the site of origin is a feature of malignant tumours.
Modes of spread of malignant tumours
- local, invasion. This is a feature of all malignant tumors and takes place along tissue spaces and facial planes
o Lymphatic spread. Most often seen in carcinomas. This can be in the form of
o Lymphatic permeation: Where the cells extend along the lymphatics as a solid core
o Lymphatic embolisation: Where a group of tumour cells break off and get carried to the draining mode
-Vascular spread : This is a common and early mode of spread for sarcomas but certain carcinomas like renal cell carcinoma and chorio carcinoma have a predilection to early vascular spread.
Vascular spread is most often due .to invasion of venous channels and can be by permeation or embolisation.
Lungs, liver, bones and brain are the common sites for vascular metastasis but
different tumours have different organ preference for metastasis, e.g. : Bronchogenic carcinoma often spreads to liver and adrenals.
-Body cavities and natural passages
o Gastrointestinal carcinomas spread to ovaries (Krukenberg’s tomour)
CONGESTION
Congestion or hyperaemia means an increase in the content of blood in an organ. It may be :
A. Active - due to increased arterial flow to the organ with dilatation of micro vessels as in
- Inflammation.
- Increased metabolic activity.
- Neurogenic blushing.
B. Passive - due to decreased venous drainage resulting in pooling of blood. There is always an associated element of oedema.
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.
Cryptococcosis
An infection acquired by inhalation of soil contaminated with the encapsulated yeast Cryptococcus neoformans, which may cause a self-limited pulmonary infection or disseminate, especially to the meninges, but sometimes to the skin, bones, viscera, or other sites.
Cryptococcosis is a defining opportunistic infection for AIDS, although patients with Hodgkin's or other lymphomas or sarcoidosis or those receiving long-term corticosteroid therapy are also at increased risk.
AIDS-associated cryptococcal infection may present with severe, progressive pneumonia with acute dyspnea and an x-ray pattern suggestive of Pneumocystis infection.
Primary lesions in the lungs are usually asymptomatic and self-limited
Pneumonia usually causes cough and other nonspecific respiratory symptoms. Rarely, pyelonephritis occurs with renal papillary necrosis development.
Most symptoms of cryptococcal meningitis are attributable to brain swelling and are usually nonspecific, including headache, blurred vision, confusion, depression, agitation, or other behavioral changes. Except for ocular or facial palsies, focal signs are rare until relatively late in the course of infections. Blindness may develop due to brain swelling or direct involvement of the optic tracts. Fever is usually low-grade and frequently absent.
Infections caused by gonorrhea
1. Acute urethritis. Mostly in males. Generally self-limiting. Dysuria and purulent discharge.
2. Endocervical infection. Purulent vaginal discharge, abnormal menses, pelvic pain. Often co-infection with other STD’s. Some women are asymptomatic.
3. Pelvic Inflammatory Disease (PID). Consequence of ascending endocervical infection. Causes salpingitis, endometriosis, bilateral abdominal pain, discharge, fever. May lead to sterility, chronic pain, and ectopic pregnancy because of loss of fallopian cilia.
4. Anorectal inflammation. Mostly in homosexual men. Pain, itching, discharge from anus.
5. Dermatitis/arthritis. Occurs after bacteremia. Skin will have papules on an erythematous base which develop into necrotic pustules. Asymmetric joint pain. These infections are susceptible to penicillin.
6. Neonatal infections. Ophthalmia neonatorum is a conjunctival infection from going through infected vagina. After one year of age, suspect child abuse.
Summary
Hepatitis A → ssRNA → Picornavirus → Oral–anal
Hepatitis B → dsDNA → Hepadnavirus → Sexual contact , Blood (needles), Perinatal
Hepatitis C → ssRNA → Flavivirus → Sexual contact , Blood (needles)
Hepatitis D → ssRNA → Deltavirus → Sexual contact, Blood (needles)
Hepatitis E → ssRNA → Calicivirus → Oral–anal