NEET MDS Lessons
General Pathology
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)
Aplasticanaemia and pancytopenia.
Aplastic anaemia is a reduction in all the formed elements of blood due to marrow hypoplasia.
Causes
- Primary or Idiopathic.
- Secondary to :
1 Drugs :
Antimetabolites and antimitotic agents.
Antiepileptics.
Phenylbutazone.
Chloramphenicol.
2 Industrial chemicals.
Benzene.
DDT and other insecticides.
TNT (used in explosives).
3 Ionising radiation
- Familial aplasia
Pancytopenia (or reduction in the formed elements of blood) can be caused by other conditions also like:
-Subleukaemic acute leukaemia.
-Megaloblastic anaemia
-S.L.E.
-hypersplenism.
-Marrow infiltration by lymphomas metastatic deposits, tuberculosis, myeloma etc
Features:
- Anaemia.
- Leucopenia upper respiratory infections.
- Thrombocytopenis :- petechiae and bruising.
Blood picture:
- Normocytic normochromic anaemia with minimal anisopoikilocytosis in aplastic anaemia. Other causes of pancytopenia may show varying degrees of anisopoikilocytosis
- Neutropenia with hypergranulation and high alkaline phosphatase.
- Low platelet counts
Bone marrow:
- Hypoplastic (may have patches of norm cellular or hyper cellular marrow) which may -> dry tap. .
- Increase in fat cells , fibroblasts , reticulum cells, lymphocytes and plasma cells
- Decrease in precursors of all three-Series.
- Underlying cause if any, of pancytopenia may be seen
Lymphocytosis:
Causes
-Infections in children and the neutropenic infections in adults.
-Lymphocytic leukaemia.
-Infectious mononucleosis.
-Toxdplasmosis.
-Myast'henia gravis.
THE ADRENAL GLANDS
ADRENAL CORTEX
The adrenal cortex synthesizes three different types of steroids:
1. Glucocorticoids (principally cortisol), which are synthesized primarily in the zona fasciculata
2. Mineralocorticoids, the most important being aldosterone, which is generated in the zona glomerulosa; and
3. Sex steroids (estrogens and androgens), which are produced largely in the zona reticularis.
ADRENAL MEDULLA
The adrenal medulla is populated by cells derived from the neural crest (chromaffin cells) and their supporting (sustentacular) cells.
They secrete catecholamines in response to signals from preganglionic nerve fibers inthe sympathetic nervous system.
Chronic myelocytic leukaemia
Commoner in adults (except the Juvenile type)
Features:
- Anaemia.
- Massive splenomegaly
- Bleeding tendencies.
- Sternal tenderness.
- Gout and skin manifestations
Blood picture:
- Marked leucocytosis of 50,-1000,000 cu.mm, often more
- Immature cells of the series with 20-50 % myelocytes
- Blasts form upto 5-10% of cells
- Basophils may be increased
- Leuocyte alkaline phosphate is reduced
- Anaemia with reticutosis and nucleated RBC
- Platelets initially high levels may fall later if patient goes into blast crisis.
Bone marrow:
- Hyper cellular marrow.
- Myeloid hyperplasia with more of immature forms, persominatly myelocytes.
Chromosomal finding. Philadelphia (Phi) chromosome is positive adult cases .It is a short chromosome due to deletion of long arm of chromosome 22 (translocated to no.9),
Juvenile type :- This is Ph1 negative has more nodal enlargement and has a worse prognosis, with a greater proneness to infections and haemorrhage
Eczematous Dermatitis
Eczematous dermatitis includes a large category of skin lesions characterized by severe pruritus and distinctive gross and microscopic features.
- type I hypersensitivity is involved with atopic dermatitis in patients who have an allergic history.
- type IV hypersensitivity is involved in contact dermatitis (poison ivy).
- acute eczematous dermatitis is characterized by a weeping, pruritic rash, while a chronic eczematous dermatitis presents with dry, scaly, plaque-like thickening of the skin, a process called lichenification.
Pulmonary edema
Pulmonary edema is swelling and/or fluid accumulation in the lungs. It leads to impaired gas exchange and may cause respiratory failure.
Signs and symptoms
Symptoms of pulmonary edema include difficulty breathing, coughing up blood, excessive sweating, anxiety and pale skin. If left untreated, it can lead to death, generally due to its main complication of acute respiratory distress syndrome.
Diagnosis
physical examination: end-inspiratory crackles during auscultation (listening to the breathing through a stethoscope) can be due to pulmonary edema. The diagnosis is confirmed on X-ray of the lungs, which shows increased vascular filling and fluid in the alveolar walls.
Low oxygen saturation and disturbed arterial blood gas readings may strengthen the diagnosis
Causes
Cardiogenic causes:
- Heart failure
- Tachy- or bradyarrhythmias
- Severe heart attack
- Hypertensive crisis
- Excess body fluids, e.g. from kidney failure
- Pericardial effusion with tamponade
Non-cardiogenic causes, or ARDS (acute respiratory distress syndrome):
- Inhalation of toxic gases
- Multiple blood transfusions
- Severe infection
- Pulmonary contusion, i.e. high-energy trauma
- Multitrauma, i.e. severe car accident
- Neurogenic, i.e. cerebrovascular accident (CVA)
- Aspiration, i.e. gastric fluid or in case of drowning
- Certain types of medication
- Upper airway obstruction
- Reexpansion, i.e. postpneumonectomy or large volume thoracentesis
- Reperfusion injury, i.e. postpulmonary thromboendartectomy or lung transplantation
- Lack of proper altitude acclimatization.
Treatment
When circulatory causes have led to pulmonary edema, treatment with loop diuretics, such as furosemide or bumetanide, is the mainstay of therapy. Secondly, one can start with noninvasive ventilation. Other useful treatments include glyceryl trinitrate, CPAP and oxygen.