THE THYROID GLAND

The thyroid gland develops embryologically from the developing pharyngeal epithelium that descends from the foramen cecum at the base of the tongue to its normal position in the anterior neck. This pattern of descent explains the occasional presence of ectopic thyroid tissue, most commonly located at the base of the tongue (lingual thyroid) or at other sites abnormally high in the neck. 

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)
 

Pleural effusion is a medical condition where fluid accumulates in the pleural cavity which surrounds the lungs, making it hard to breathe.

Four main types of fluids can accumulate in the pleural space:

Serous fluid (hydrothorax)

Blood (hemothorax)

Lipid (chylothorax)

Pus (pyothorax or empyema)

Causes:

Pleural effusion can result from reasons such as:

• Cancer, including lung cancer or breast cancer
• Infection such as pneumonia or tuberculosis
• Autoimmune disease such as lupus erythematosus
• Heart failure
• Bleeding, often due to chest trauma (hemothorax)
• Low oncotic pressure of the blood plasma
• lymphatic obstruction
• Accidental infusion of fluids

Congestive heart failure, bacterial pneumonia and lung cancer constitute the vast majority of causes in the developed countries, although tuberculosis is a common cause in the developing world.

Diagnosis:

1. Gram stain and culture - identifies bacterial infections
2. Cell count and differential - differentiates exudative from transudative effusions
3. Cytology - identifies cancer cells, may also identify some infective organisms
4. Chemical composition including protein, lactate dehydrogenase, amylase, pH and glucose - differentiates exudative from transudative effusions
5. Other tests as suggested by the clinical situation - lipids, fungal culture, viral culture, specific immunoglobulins

Osteopetrosis (Albers-Schönberg disease or marble bone disease) 

is a group of rare genetic disorders characterized by reduced osteoclast-mediated bone resorption and therefore defective bone remodelling. The bones are solid and heavy with no medullary canal, long ends are bulbous, small neural foramina compress nerves. The affected bone is grossly dense but fractures occur readily like a piece of chalk. 

Patients frequently have cranial nerve compressions by the surrouding bone, and recurrent infections. The latter is attributable to diminished hematopoiesis resulting from reduced marrow space with impressive hepatosplenomegaly due to extramedullary hematopoiesis 
 
a. Caused by abnormal osteoclasts. This results in defective bone remodeling (i.e., abnormally low bone resorption) and increased bone density, which may invade into bone marrow space.
b. Causes severe defects in infants, including:
(1) Anemia and infections—caused by decreased bone marrow.
(2) Blindness, deafness, paralysis of facial muscles—caused by the narrowing of cranial nerve foramina.
(3) Is life-threatening.
(4) Oral findings include delayed eruption of teeth.
c. Disease is less severe in adults

Measles (rubeola) 

-incubation period 7 to 14 days 

-begins with fever (up to 40 degrees C), cough, conjunctivitis (photophobia is first sign), and coryza (excessive mucous production)Æfollowed by Koplik's spots (red with white center) in the mouth, posterior cervical Lymphadenopathy, and a generalized, blanching, maculopapular, brownish-pink rash (viral induced vasculitis) beginning at the hairline and extending down over the body which gradually resolves in 5 days with some desquamation. 

Hypoparathyroidism

Hypoparathyroidism is a condition of reduced or absent PTH secretion, resulting in hypocalcaemia and hyperphosphataemia. It is far less common than hyperparathyroidism.

The causes of hypoparathyroidism are:
- Removal or damage of the parathyroid glands during thyroidectomy—most common cause of hypoparathyroidism resulting from inadvertent damage or removal.
- Autoimmune parathyroid disease—usually occurs in patients who have another autoimmune endocrine disease, e.g. Addison’s disease (autoimmune endocrine syndrome type 1).
- Congenital deficiency (DiGeorge syndrome)— rare, congenital disorder caused by arrested development of the third and fourth branchial arches, resulting in an almost complete absence of the thymus and parathyroid gland.

The effects of hypoparathyroidism are:
- ↓ release of Ca²⁺ from bones. 
- ↓ Ca²⁺ reabsorption but ↑ PO ₄³⁻ re absorption by the kidneys
- ↓ 1-hydroxylation of 25-hydroxyvitamin D by kidney.

Most symptoms of hypoparathyroidism are those of hypocalcaemia:
- Tetany—muscular spasm provoked by lowered plasma Ca 2+ 
- Convulsions.
- Paraesthesiae.
- Psychiatric disturbances, e.g. depression, confusional state and even psychosis.
- Rarely—cataracts, parkinsonian-like movement disorders, alopecia, brittle nails.

Management is by treatment with large doses of oral vitamin D; the acute phase requires intravenous calcium and calcitriol (1,25-dihydroxycholecalciferol, i.e.  activated vitamin D).