Is found at autopsy which is incompatible with life,

(b) Where a lesion is found which may have caused death or which may have precipitated death, but which is also known to be compatible with continued life.

(Ill) Obscure Causes : Where no lesion is found at autopsy, or if a lesion is found it is of a minimal or indefinite nature.

NATURAL CAUSES : Where a lesion is found at autopsy which is not compatible with life : In this category, the structural abnormalities establish beyond any doubt the identity of the disease which caused death. It is apparent that the lesions observed are incompatible with life because of its nature, site or extent, and they are ante-mortem in origin. The examples are : massive pulmonary thromboembolism, spontaneous intracerebral haemorrhage, ruptured myocardial infarct, rupture of an aortic aneurysm.

(B) Where a lesion is found at autopsy which is known to cause death : This category includes deaths in which some lesion is found at autopsy which may have caused death, but which is also compatible with continued life, e.g., arteriosclerosis of the coronary arteries, advanced chronic heart diseases, lobar pneumonia, etc. The autopsy does not reveal any other reasonable explanation for death, and the location, nature, severity and extent of the anatomical changes are sufficient to cause death, but it is not a conclusive proof. In such cases, the clinical history is important. In the case of coronary arteriosclerosis, if the deceased had several attacks of angina pectoris before his death, it can be reasonably assumed to be the cause of death. If the clinical history is unusual, the possibilities suggested by the history should be excluded before the death is attributed to the lesion.

Stenosing coronary atherosclerosis can cause sudden death, in which the autopsy may reveal a few scattered foci or only a single site of significant luminal narrowing, and there may be no recent vascular occlusive lesion. In most cases of sudden coronary death, a fresh thrombus or a recent myocardial infarct is not found al autopsy. In these cases, correlation of the morbid anatomy with the suddenness of death must be based on hypotheses. Emotional stress, e.g., anger, fear, joy, apprehension, etc., can precipitate acute failure in persons with organic heart disease, especially of the coronary atherosclerotic type. Emotional excitement significantly increases the workload of the heart which can overtax the limits of tolerance of damaged, labouring heart. In a normal person sudden release of adrenaline due to extreme terror can initiate ventricular fibrillation and death. Sudden deaths following assaults or even threats may occur due to existing heart disease.

Such events may be encountered in criminal charges arising out of collapse during fights, in minor assaults upon old persons, in litigation related to death from workstress, etc.

Sufferers from asthma and epilepsy can die suddenly and unexpectedly for no obvious reasons.

Un-natural Causes : (A) Where a lesion is found at autopsy which is not compatible with life : In some deaths, injuries may be found at autopsy which are incompatible with life in any person, e.g., decapitation, crushing of the head, avulsion of the heart from the large blood vessels, If they are ante-mortem, they are the definite cause of death.

(B) A lesion is found at autopsy which may have caused or precipitated death, but is compatible with life : At autopsy certain injuries may be found which from their nature, site or extent may not appear to be sufficient to cause death in a healthy person. But such injury may be the cause of death due to some complication resulting directly from the injury, but which is not demonstrable at autopsy. The degree of shock or the extent of haemorrhage following an injury cannot be assessed at autopsy. In such cases, the absence of any other adequate cause of death, and a consideration of the circumstances of the injury and of the symptoms found, may enable the doctor to attribute death to the injury with reasonable certainty.

In some cases, an injury may not appear to be sufficient to cause death, but some natural disease may be present which is known to cause death, e.g., coronary arteriosclerosis. In such cases, the circumstances of death and the symptoms found at the time of collapse may suggest that the death was precipitated by the injury.

NEGATIVE AUTOPSY : When gross and microscopic examination, toxicological analyses and

laboratory investigations fail to reveal a cause of death, the autopsy is considered to be negative. Two to 5% of all autopsies are negative. Majority of obscure autopsies are in young adults. A negative autopsy may be due to; (1) Inadequate history : Deaths from vagal inhibition, status epilepticus, hypersensitivity reaction, etc. may not show any anatomical findings. If death results from laryngeal spasm in drowning, no anatomical findings may be present. (2) Inadequate external examination :The presence of fresh and old needle marks may be missed on cursory examination in a drug addict. The burn may be missed in electrocution. Death from snake bites and insect bites cannot be explained unless the bite marks are identified. (3) Inadequate or improper internal examination : Air embolism and pneumothorax are often missed. (4) Insufficient laboratory examinations. (5) Lack of toxicological analysis. (6) Lack of training of the doctor.

Obscure autopsies are those which do not show a definite cause for death, in which there are minimal, indefinite or obscure findings, or even no positive findings at all. They are a source of confusion to any pathologist. Frequently, these deaths are due to obscure natural causes, but they may be due to certain types of injury or complications of injury, or to poisoning. Mild degrees of natural disease should not be implicated unless other possibilities are most carefully eliminated.

The obscure causes are : (1) Natural diseases : (a) With obscure or some microscopic findings, (b) death precipitated by emotion, work-stress, and (c) with functional failure, such as epilepsy, paroxysmal fibrillation.

(2) Biochemical disturbances : (a) Uraemia,

diabetes, potassium deficiency, and (b) respiratory

pigment disorders, such as anaemic anoxia,

porphyria.

(3) Endocrine dysfunction: Adrenal