NEET MDS Lessons
General Pathology
Hyperpituitarism
Causes
A. Pituitary; usually anterior lobe
1. Adenoma (the most common cause)
2. Hyperplasia
3. Carcinoma
B. Extra-pituitary causes
1. Hormone producing extra-pituitary tumors (ectopic hormone production)
2. Certain hypothalamic disorders
Pituitary adenomas are classified according to the hormone(s) produced by the neoplastic cells; these are detected by immunohistochemically-stained tissue sections. Pituitary adenomas can be functional (associated with hormone excess with their related clinical manifestations) or silent.
Pathogenesis
Guanine nucleotide-binding protein (G-protein) mutations are the best characterized molecular abnormalities. Such mutations eventuate in a persistent increase in intracellular cAMP, which is a potent mitogenic stimulus promoting cellular proliferation and hormone synthesis and secretion. In the setting of MEN-1 syndrome there are mutations in the MEN-1 (menin) gene.
Gross features
• Adenomas are usually soft & well-circumscribed
• Larger lesions extend superiorly through the sellar diaphragm compressing the optic chiasm and adjacent structures .
• Invasive adenomas refer to nonencapsulated tumors that infiltrate adjacent bone, dura, and even brain.
Microscopic features.
• Adenomas are composed of monomorphic, polygonal cells displayed in sheets, cords, or papillae. Their nuclei may be uniform or pleomorphic but the mitotic activity is scanty. The cytoplasm of the constituent cells may be acidophilic, basophilic, or chromophobic.
• The connective tissue is scanty that is why many lesions are soft & even gelatinous in consistency.
Prolactinomas are the most common type of hyperfunctioning pituitary adenoma.
Hyperprolactinemia causes amenorrhea, galactorrhea, loss of libido, and infertility.
Growth Hormone-Producing Adenomas (somatotroph cell adenomas) are the second most common type of functional pituitary adenoma. Because the clinical manifestations of excessive growth hormone may be subtle, the tumor may be quite large by the time they come to clinical attention. If such tumors occur before closure of epiphyses (prepubertal children), excessive levels of growth hormone result in gigantism. If elevated levels persist, or present after closure of the epiphyses, individuals develop acromegaly.
Corticotroph Cell Adenomas are mostly small (microadenomas) at the time of diagnosis. They may be clinically silent or cause hypercortisolism referred to as Cushing disease
Other Anterior Pituitary Neoplasms
• Gonadotroph adenomas (luteinizing hormone [LH]-producing and follicle-stimulating hormone [FSH]producing)
• Thyrotroph (thyroid-stimulating hormone [TSH]-producing) adenomas
• Nonfunctioning pituitary adenomas (hormone-negative (null cell) adenomas) Nonfunctioning adenomas constitute approximately 25% of all pituitary tumors; they typically present through their mass effects.
Amyotrophic lateral sclerosis (Lou Gehrig’s disease)
a. Characterized by the rapid degeneration of motor neurons in the spinal cord and corticospinal tracts.
b. More common in men in their 50s.
c. Clinically, the disease results in rapidly progressive muscle atrophy due to denervation. Other symptoms include fasciculations, hyperreflexia, spasticity, and pathologic reflexes. Death usually occurs within a few years from onset, usually by respiratory failure or infection.
Anemia (Disorder of Hematopoietic System) - Probably the most common effect of nutritional deficiency. Any factor that decreases hematopoiesis can cause an anemia.
A. Iron deficiency - Widely recognized as the most important cause of anemia, It is indicated that ½ of all pregnant women and infants are affected, as are ~13% of all adult women.
1. Dietary factors - Availability of iron from different food sources and mixtures.
2. Malabsorption – One third of patients with inflammatory bowel disease (IBD) have recurrent anemia and 30% or more of patients who have had partial gastrectomy will develop iron deficiency anemia.
3. Blood loss - Menses, gastrointestinal bleeding
4. Increased demand - Pregnancy, growth in children.
5. Congenital - Atransferrinemia
6. Importance of multiple factors.
7. Pathophysiology - Initially iron is mobilized from reticuloendothelial stores and increased intestinal absorption occurs. Total iron stores are depleted, serum iron levels fall. In severe cases in peripheral blood, the red cells become smaller (microcytic) and their hemoglobin content is reduced (hypochromic).
B. Megaloblastic anemias- Characterized by the presence of abnormal WBCs and RBCs. In severe cases, megaloblasts (abnormal red cell precursors) may be present. These anemias are a consequence of disordered DNA synthesis.
1. Folate deficiency - Can be caused by:
a. Dietary deficiency
b. Malabsorption (celiac disease)
c. Increased demand (pregnancy & lactation)
d. Drugs - methotrexate, anticonvulsants, oral contraceptives, alcoholism.
e. Liver disease
2. Cobalamin (vitamin B12) deficiency - Almost always a secondary disorder that can be caused by:
a. Intrinsic factor deficiency (pernicious anemia due to autoimmune destruction of the gastric mucosa)
b. Malabsorption
3. Pyridoxine (vitamin B6) deficiency- most commonly associated with alcoholism.
C. Other factors known to be frequently associated with anemia would include protein-calorie malnutrition, vitamin C deficiency, and pyridoxine deficiency (usually associated with alcoholism).
D. Other anemias not particularly associated with nutritional disease would include hemolytic anemia
(decreased red cell life span) and aplastic anemia (failure of marrow to produce new cells).
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)
Cardiac tamponade
A. Caused by accumulation of fluid in the pericardium. This severe condition can quickly impair ventricular filling and rapidly lead to decreased cardiac output and death.
1. Signs and symptoms include:
a. Hypotension.
b. Jugular venous distention.
c. Distant heart sounds.
ADRENOCORTICAL TUMORS
Functional adenomas are commonly associated with hyperaldosteronism and with Cushing syndrome, whereas a virilizing neoplasm is more likely to be a carcinoma. Determination of of the functional status of a tumor is based on clinical evaluation and measurement of the hormone or its metabolites. In other words, functional and nonfunctional adrenocortical neoplasms cannot be distinguished on the basis of morphologic features.
Patholgical features
Adrenocortical adenomas
- They are generally small, 1 to 2 cm in diameter.
- On cut surface, adenomas are usually yellow to yellow-brown due to presence of lipid within the neoplastic cells
- Microscopically, adenomas are composed of cells similar to those populating the normal adrenal cortex. The nuclei tend to be small, although some degree of pleomorphism may be encountered even in benign lesions ("endocrine atypia"). The cytoplasm ranges from eosinophilic to vacuolated, depending on their lipid content.
Adrenocortical carcinomas
These are rare and may occur at any age, including in childhood.
- Carcinomas are generally large, invasive lesions.
- The cut surface is typically variegated and poorly demarcated with areas of necrosis, hemorrhage, and cystic change.
- Microscopically, they are composed of well-differentiated cells resembling those of cortical adenomas or bizarre, pleomorphic cells, which may be difficult to distinguish from those of an undifferentiated carcinoma metastatic to the adrenal.
OEDEMA
Excessive accumulation of fluid in the extra vascular compartment (intersttitial tissues). This includes ascites (peritoneal sac), hydrothorax (pleural cavity) hydropericardium (pericardial space) and anasarca (generalised)
Factors which tend to accumulate interstitial fluid are:
- Intravascular hydrostatic pressure
- Interstitial osmotic pressure.
- Defective lymphatic drainage.
- Increased capillary permeability.
Factors that draw fluid into circulation are:
- Tissue hydrostatic-pressure (tissue tension).
- Plasma osmotic pressure,
Oedema fluid can be of 2 types:
A. Exudate.
It is formed due to increased capillary permeability as in inflammation.
B. Transudate
Caused by alterations of hydrostatic and osmotic pressures.
|
|
Exudate |
Transudate |
|
Specific Gravity |
>1.018 |
1.012 |
|
Protein Content |
High |
Low |
|
Nature of Protein |
All Plasma Protein |
Albumin mostly |
|
Spontaneous Clotting |
High(Inflammatory Cells) |
Low |
Local Oedema
1. Inflammatory oedema. Mechanisms are.
- Increased capillary permeability.
- Increased vascular hydrostatic pressure.
- Increased tissue osmotic pressure.
2.Hypersensitivity reactions especially types I and III
3. Venous obstruction :
- Thrombosis.
- Pressure from outside as in pregnancy, tourniquets.
4. Lymphatic obstruction:
- Elephantiasis in fillariasis
- Malignancies (Peau de orange in breast cancer).
Generalized Oedema
1. Cardiac oedema
Factors :Venous pressure increased.
2. Renal oedema
- Acute glomerulonephritis
- Nephrotic syndrome
3. Nutritional (hypoproteinaemic) oedema. it is seen in
- Starvation and Kwashiorkor
- Protein losing enteropathy
4. Hepatic oedema (predominantly ascites)
Factors:
- Fall in plasma protein synthesis
- Raised regional lymphatic and portal venous pressure
5. Oedema due to adrenal corticoids
As in Cushing's Syndrome
Pulmonary oedema
- Left heart failure and mitral stenosis.
- Rapid flv infusion specially in a patient of heart failure.