Forensic Medicine & Toxicology
High-yield MBBS Forensic Medicine & Toxicology question bank — medical jurisprudence, identification, thanatology, injuries, asphyxia, forensic sexology and toxicology, at Reddy’s / Parikh depth.
12chapters144questions77High-Yield
Definition
Asphyxia is a condition in which the supply of oxygen to the tissues is impaired, with accumulation of carbon dioxide.
Classification
- Mechanical — hanging, strangulation, throttling, suffocation, drowning, traumatic asphyxia, choking
- Pathological — laryngeal oedema, bronchial obstruction, pneumothorax, respiratory paralysis
- Toxic — carbon monoxide, cyanide, irritant gases (interfere with oxygen transport or utilisation)
- Environmental — high altitude, entrapment in confined space
- Postural (crucifixion) asphyxia — body position preventing respiration
Classical Signs (‘triad’ and others)
- Cyanosis — blue discoloration of face, lips and nails
- Petechial haemorrhages (Tardieu spots) — conjunctivae, eyelids, face, pleura, epicardium; due to raised venous pressure and hypoxic capillary damage
- Congestion and oedema of face and internal organs
- Fluidity of blood — due to fibrinolysins (also occurs in other rapid deaths)
- Right heart dilated, left heart empty; frothy fluid in air passages
- All signs are non-specific — diagnosis rests on the whole picture and circumstances
The classical signs reflect venous congestion, not asphyxia specifically. Sign Basis Cyanosis Deoxygenated haemoglobin Tardieu spots Raised venous pressure Fluid blood Fibrinolysins Applied
- Petechiae are the most useful but not diagnostic — also seen in cardiac failure and crush injury
- Stages: dyspnoea → convulsions → apnoea; death in about 3–5 minutes
🔑KEY POINTS TO REMEMBER- Asphyxia is impaired tissue oxygenation with carbon dioxide retention.
- Types: mechanical, pathological, toxic, environmental, postural.
- Signs — cyanosis, Tardieu spots, congestion, fluid blood — are all non-specific.
📚SOURCES: The Essentials of Forensic Medicine and Toxicology (K.S. Narayan Reddy); Textbook of Forensic Medicine and Toxicology (V.V. Pillay); Modi’s Textbook of Medical Jurisprudence and Toxicology.Definition
Hanging is a form of asphyxial death in which the body is suspended and the constricting force on the neck is the weight of the body itself.
Types & Mechanism
- Complete — body fully suspended; partial (incomplete) — some part touches the ground (commoner; even a few kilograms suffice)
- Typical — knot at the nape of the neck, ligature symmetrical
- Atypical — knot elsewhere (commoner in practice)
- Mechanisms of death: asphyxia, venous congestion, cerebral anaemia (carotid compression), vagal inhibition, cervical spine injury (judicial hanging)
- Only 2 kg compresses jugular veins, 5 kg carotids, 15 kg trachea, 30 kg vertebral arteries
Autopsy Findings
- Ligature mark — oblique, non-continuous, placed high on the neck above the thyroid cartilage, deepest opposite the knot
- Mark is parchment-like, dry, hard, yellow-brown
- Face pale in typical complete hanging (carotids occluded); congested if partial
- Dribbling of saliva from the angle of the mouth — a vital (antemortem) sign
- Neck structures: fracture of hyoid or thyroid cartilage uncommon; Amussat sign (transverse carotid intimal tear), Simon sign (lumbar disc haemorrhage)
- Postmortem lividity in the lower limbs and forearms (‘glove and stocking’ distribution)
Only a small fraction of body weight is needed to occlude neck vessels. Feature Hanging Ligature mark Oblique, high, non-continuous Saliva dribbling Present (vital sign) Manner Usually suicidal Applied
- Almost always suicidal; accidental and judicial forms occur; homicidal hanging is very rare
- Dribbling of saliva cannot be produced after death — valuable evidence
🔑KEY POINTS TO REMEMBER- Hanging uses the body’s own weight; only 2–5 kg occludes neck vessels.
- Ligature mark is oblique, high on the neck and non-continuous.
- Dribbling of saliva is a vital sign; hanging is almost always suicidal.
📚SOURCES: The Essentials of Forensic Medicine and Toxicology (K.S. Narayan Reddy); Textbook of Forensic Medicine and Toxicology (V.V. Pillay); Modi’s Textbook of Medical Jurisprudence and Toxicology.Definition
Strangulation is constriction of the neck by a force other than the body weight; throttling is manual strangulation using the hands.
Ligature Strangulation
- Constricting force applied by a ligature tightened by hand or other means
- Ligature mark is horizontal (transverse), continuous, and low on the neck at or below the thyroid cartilage
- Mark is uniformly deep all round
- Face markedly congested and cyanosed, with abundant petechiae
- Neck structures often injured; fracture of hyoid, thyroid and cricoid commoner than in hanging
- Almost always homicidal
Throttling (manual strangulation)
- Always homicidal — cannot be self-inflicted (grip relaxes on losing consciousness)
- Fingernail abrasions (crescentic) and discoid bruises on the neck
- Fracture of the hyoid bone and superior horns of the thyroid cartilage — common, especially in the elderly
- Deep bruising of neck muscles — demonstrated by bloodless neck dissection
- Marked facial congestion, cyanosis and petechiae
- Mugging (garrotting) — forearm used from behind
Both are constricting forces independent of body weight, and both suggest homicide. Feature Ligature Throttling Mark Transverse band Nail abrasions Hyoid fracture Common Very common Manner Homicidal Always homicidal Applied
- Always perform a bloodless neck dissection after removing brain and thoracic organs
- Preserve nail clippings of the deceased for the assailant’s DNA
🔑KEY POINTS TO REMEMBER- Strangulation mark is transverse, continuous and low on the neck.
- Throttling shows crescentic nail abrasions and hyoid fracture — always homicidal.
- Bloodless neck dissection is essential to demonstrate deep bruising.
📚SOURCES: The Essentials of Forensic Medicine and Toxicology (K.S. Narayan Reddy); Textbook of Forensic Medicine and Toxicology (V.V. Pillay); Modi’s Textbook of Medical Jurisprudence and Toxicology.Definition
Drowning is asphyxial death caused by the aspiration of fluid into the air passages following submersion.
Types & Mechanism
- Typical (wet) drowning — fluid aspirated into the lungs
- Dry drowning — laryngeal spasm prevents entry of water (about 10–15%)
- Immersion (hydrocution) syndrome — sudden vagal inhibition from cold water on the skin or entry into the nose
- Secondary (post-immersion) drowning — death hours to days later from pulmonary oedema and ARDS
- Stages: surprise, resistance, deep respiration, convulsions, apnoea
Autopsy Findings
- Fine, white, tenacious froth (leathery foam) at the mouth and nostrils and in the air passages — the most reliable sign of antemortem drowning
- Lungs voluminous, ballooned (emphysema aquosum), retaining rib impressions; heavy and oedematous
- Cutis anserina (goose skin) and washerwoman’s hands and feet — signs of immersion, not of drowning
- Cadaveric spasm gripping weeds, mud or grass — proves the person was alive on entering the water
- Water, sand, weeds and mud in the stomach and air passages
- Paltauf haemorrhages beneath the pleura
Froth forms only if the person was breathing on entering the water. Sign Indicates Fine froth Antemortem drowning Washerwoman’s hands Immersion only Cadaveric spasm Alive at entry Applied
- Distinguish signs of drowning from mere signs of immersion
- Diatom test supports the diagnosis in decomposed bodies
🔑KEY POINTS TO REMEMBER- Fine white tenacious froth in the airways is the most reliable sign of drowning.
- Dry drowning (laryngeal spasm) occurs in 10–15% of cases.
- Washerwoman’s hands indicate immersion, not drowning.
📚SOURCES: The Essentials of Forensic Medicine and Toxicology (K.S. Narayan Reddy); Textbook of Forensic Medicine and Toxicology (V.V. Pillay); Modi’s Textbook of Medical Jurisprudence and Toxicology.Definition
Suffocation is asphyxia caused by obstruction of the air passages or by deprivation of oxygen, without constriction of the neck.
Types
- Smothering — closure of the mouth and nostrils by hand, cloth or pillow; abrasions and bruises around mouth and nose
- Choking (internal obstruction) — foreign body impacted in the air passages: food bolus, denture, coin, marble, betel nut
- Gagging — cloth pushed into the mouth to prevent speech; usually accidental death during robbery
- Overlaying — accidental smothering of an infant by an adult during sleep
- Traumatic asphyxia — chest compression
- Suffocation by irrespirable gases — confined spaces, sewers, wells
Autopsy & Medicolegal Aspects
- Classical asphyxial signs — cyanosis, petechiae, congestion
- Smothering — injuries around mouth and nose; may be absent if a soft pillow used or the victim is an infant or elderly
- Bruising of the inner surface of the lips against the teeth
- Choking — foreign body must be sought before disturbing the airway
- Manner: smothering usually homicidal (infants and the helpless); choking usually accidental
- Findings may be entirely negative in infant smothering — scene investigation is vital
Smothering of an infant may leave no autopsy findings at all. Type Mechanism Manner Smothering Mouth/nose closed Homicidal Choking Internal obstruction Accidental Gagging Cloth in mouth Accidental Applied
- Suspect smothering in an infant with unexplained death and facial marks
- Always inspect the airway before removing the tongue and larynx
🔑KEY POINTS TO REMEMBER- Suffocation obstructs air passages without neck constriction.
- Types: smothering, choking, gagging, overlaying, traumatic asphyxia.
- Infant smothering may leave no findings — scene investigation is crucial.
📚SOURCES: The Essentials of Forensic Medicine and Toxicology (K.S. Narayan Reddy); Textbook of Forensic Medicine and Toxicology (V.V. Pillay); Modi’s Textbook of Medical Jurisprudence and Toxicology.Definition
Hanging and ligature strangulation both compress the neck, but differ in the constricting force and in almost every autopsy finding.
Hanging
- Constricting force is the weight of the body
- Ligature mark oblique, non-continuous, high on the neck above the thyroid cartilage
- Mark deepest opposite the knot
- Face usually pale; petechiae few
- Dribbling of saliva present; neck structures rarely fractured
- Almost always suicidal
Ligature Strangulation
- Constricting force applied by hand or other external means
- Mark transverse, continuous, low on the neck at or below the thyroid cartilage
- Mark uniformly deep
- Face markedly congested and cyanosed; abundant petechiae
- No saliva dribbling; hyoid and thyroid fractures common; deep neck muscle bruising
- Almost always homicidal; signs of struggle and defence wounds present
Direction and level of the ligature mark are the key discriminators. Feature Hanging Strangulation Mark Oblique, high Transverse, low Continuity Non-continuous Continuous Face Pale Congested Manner Suicidal Homicidal Applied
- A body may be hanged after strangulation to simulate suicide — look for a second mark
- Dribbling of saliva is the single most useful vital sign of hanging
🔑KEY POINTS TO REMEMBER- Hanging: oblique, high, non-continuous mark; pale face; suicidal.
- Strangulation: transverse, low, continuous mark; congested face; homicidal.
- Saliva dribbling favours hanging; hyoid fracture favours strangulation.
📚SOURCES: The Essentials of Forensic Medicine and Toxicology (K.S. Narayan Reddy); Textbook of Forensic Medicine and Toxicology (V.V. Pillay); Modi’s Textbook of Medical Jurisprudence and Toxicology.Definition
The diatom test detects microscopic algae (diatoms) in body tissues to confirm antemortem drowning.
Principle & Technique
- Diatoms are unicellular algae with an indestructible silica (silicaceous) shell
- If a person is alive on entering water, diatoms are inhaled, cross the alveoli, enter the circulation and are carried to distant organs
- Detected in bone marrow (femur, sternum), liver, kidney, brain — bone marrow is the best sample because it is protected from contamination
- Acid digestion technique — tissue destroyed by nitric or sulphuric acid; silica shells survive and are examined microscopically
- A control sample of the water is examined for comparison of species
Interpretation & Limitations
- Diatoms in distant organs (especially bone marrow) indicate the circulation was functioning → antemortem drowning
- Diatoms in the lungs alone are not conclusive — they can enter passively after death
- Especially valuable in decomposed bodies where other signs are lost
- Species and number should match the water in which the body was found
- False positives — diatoms occur in food, air and drinking water
- False negatives — dry drowning, low diatom content in the water
Only a beating heart can carry diatoms to distant bone marrow. Sample Value Bone marrow Best, protected Liver, kidney Good Lung alone Not conclusive Applied
- Matching diatom species with the water may indicate where drowning occurred
- Interpret alongside froth, lung findings and the scene
🔑KEY POINTS TO REMEMBER- Diatoms have indestructible silica shells and survive acid digestion.
- Diatoms in bone marrow indicate the circulation was active — antemortem drowning.
- Diatoms in lungs alone are not conclusive; false positives and negatives occur.
📚SOURCES: The Essentials of Forensic Medicine and Toxicology (K.S. Narayan Reddy); Textbook of Forensic Medicine and Toxicology (V.V. Pillay); Modi’s Textbook of Medical Jurisprudence and Toxicology.Definition
Café coronary is sudden death from choking on a bolus of food that closely mimics a heart attack.
Mechanism & Circumstances
- A large, poorly chewed bolus of meat or other food impacts in the larynx or pharynx
- Causes acute airway obstruction and often vagal inhibition from laryngeal stimulation
- Death may be instantaneous — more rapid than pure asphyxia would explain
- Typically occurs while eating in a restaurant, hence the name
- Predisposed by alcohol intoxication, ill-fitting dentures or absent teeth, old age, laughing or talking while eating, neurological disease, sedatives
Presentation & Importance
- Victim suddenly stops eating, cannot speak or cough, clutches the throat (universal choking sign), becomes cyanosed and collapses
- Mistaken for myocardial infarction — hence ‘café coronary’
- Autopsy: food bolus impacted in the airway; asphyxial signs; heart normal
- Manner is accidental
- Prevented and treated by the Heimlich manoeuvre (abdominal thrusts)
- Examine the airway before disturbing the neck organs at autopsy
Vagal inhibition explains why death is faster than asphyxia alone. Feature Detail Cause Food bolus Risk Alcohol, dentures Treatment Heimlich manoeuvre Applied
- Prompt abdominal thrusts can be life-saving
- Always inspect the larynx before removing the tongue at autopsy
🔑KEY POINTS TO REMEMBER- Café coronary is sudden death from a food bolus obstructing the larynx.
- Mimics myocardial infarction; predisposed by alcohol and poor dentition.
- Accidental in manner; treated by the Heimlich manoeuvre.
📚SOURCES: The Essentials of Forensic Medicine and Toxicology (K.S. Narayan Reddy); Textbook of Forensic Medicine and Toxicology (V.V. Pillay); Modi’s Textbook of Medical Jurisprudence and Toxicology.Definition
Autoerotic asphyxia is accidental death occurring during solitary sexual activity in which cerebral hypoxia is used to heighten sensation.
Scene Features
- Victim usually a young male, found alone in a locked room
- Elaborate self-rescue mechanism present — slip knot, padding under the ligature, keys or scissors within reach
- Padding between ligature and neck to avoid marks
- Presence of pornographic material, mirrors, cross-dressing or bondage apparatus
- No suicide note; no history of depression
- Evidence of repeated previous practice — grooves in beams, old ligature marks
Medicolegal Importance
- Manner is accidental — death results from failure of the escape mechanism
- Commonly misinterpreted as suicide or homicide
- Relatives may alter the scene before police arrive, obscuring the diagnosis
- Correct classification matters for insurance claims and family reputation
- Diagnosis rests almost entirely on scene investigation, not autopsy findings
- Autopsy shows features of hanging or asphyxia only
The presence of a self-rescue device is what marks it as accidental. Feature Significance Escape mechanism Accidental, not suicide Padding Avoids marks No note Against suicide Applied
- Careful, tactful scene documentation prevents a wrong verdict
- Insurance often excludes suicide but covers accidental death
🔑KEY POINTS TO REMEMBER- Autoerotic asphyxia is accidental death during solitary sexual activity.
- Scene shows a self-rescue mechanism, padding and no suicide note.
- Diagnosis depends on scene investigation; often misclassified as suicide.
📚SOURCES: The Essentials of Forensic Medicine and Toxicology (K.S. Narayan Reddy); Textbook of Forensic Medicine and Toxicology (V.V. Pillay); Modi’s Textbook of Medical Jurisprudence and Toxicology.Definition
Traumatic asphyxia (crush asphyxia) is asphyxia caused by mechanical fixation of the chest preventing respiratory movement.
Causes
- Crowd stampedes and crushing in panicking crowds
- Building or wall collapse, earthquakes, landslides, mine accidents
- Vehicle overturning onto the chest; being pinned under machinery
- Burial in earth, sand or grain
- Overlaying of infants
- Chest fixed so the thorax cannot expand — respiration mechanically impossible
Autopsy Findings
- Deep bluish-purple (violaceous) discoloration of the face, neck and upper chest — the classic ‘masque ecchymotique’
- Sharp line of demarcation at the level of compression
- Intense petechiae of face, conjunctivae and neck; subconjunctival haemorrhage
- Marked congestion and oedema of the head and neck; protrusion of eyes and tongue
- Rib fractures, lung contusion, pneumothorax may be present
- Death results from mechanical prevention of breathing, not airway obstruction
Blood is forced back into the head and neck by the compressed thorax. Feature Detail Sign Masque ecchymotique Demarcation At compression level Manner Usually accidental Applied
- Common in religious gatherings and stampedes in India
- Manner is almost always accidental; occasionally homicidal (burking)
🔑KEY POINTS TO REMEMBER- Traumatic asphyxia results from mechanical fixation of the chest.
- Masque ecchymotique — violaceous head and neck with sharp demarcation.
- Usually accidental, from stampedes and structural collapse.
📚SOURCES: The Essentials of Forensic Medicine and Toxicology (K.S. Narayan Reddy); Textbook of Forensic Medicine and Toxicology (V.V. Pillay); Modi’s Textbook of Medical Jurisprudence and Toxicology.Definition
Burking is a method of homicide combining smothering with traumatic asphyxia, named after the murderer William Burke.
Historical Background & Method
- Named after William Burke and William Hare, Edinburgh, 1827–1828
- They killed victims and sold the bodies to anatomy schools for dissection
- The assailant closed the mouth and nose while kneeling or sitting on the chest
- Combines smothering and traumatic asphyxia
- Victims were usually intoxicated, elderly or feeble and unable to resist
- Sixteen victims before Burke was convicted and hanged
Autopsy Findings & Significance
- Injuries around the mouth and nose from smothering
- Bruising of the chest wall, rib fractures, and facial congestion from compression
- Marked petechiae, cyanosis and congestion
- Few external injuries — the method left bodies apparently undamaged, making them saleable
- Historical importance: led to the Anatomy Act of 1832, regulating the legal supply of bodies for dissection
- Manner is always homicidal
The method was designed to leave the body outwardly unmarked. Component Effect Smothering Airway closed Chest compression Traumatic asphyxia Result Few external marks Applied
- Suspect burking in an unexplained death with facial and chest bruising
- The case directly prompted legal reform of anatomical dissection
🔑KEY POINTS TO REMEMBER- Burking combines smothering with traumatic asphyxia by chest compression.
- Named after William Burke, who sold bodies to anatomy schools (1827–28).
- Always homicidal; leaves few external injuries; led to the Anatomy Act 1832.
📚SOURCES: The Essentials of Forensic Medicine and Toxicology (K.S. Narayan Reddy); Textbook of Forensic Medicine and Toxicology (V.V. Pillay); Modi’s Textbook of Medical Jurisprudence and Toxicology.Definition
Fresh-water and salt-water drowning differ in the direction of fluid and electrolyte movement across the alveolar membrane.
Fresh-Water Drowning
- Fresh water is hypotonic to blood
- Water is rapidly absorbed from alveoli into the circulation
- → Haemodilution and hypervolaemia
- → Haemolysis releasing potassium → hyperkalaemia
- → Ventricular fibrillation — death within about 4–5 minutes
- Surfactant is washed out, causing alveolar collapse
Salt-Water Drowning
- Sea water is hypertonic to blood
- Water is drawn from the circulation into the alveoli
- → Haemoconcentration and hypovolaemia
- → Massive pulmonary oedema
- → Death from hypoxia and circulatory failure, more slowly — about 8–12 minutes
- Survival chances are therefore better in salt water
Tonicity relative to blood determines the direction of fluid shift. Feature Fresh water Salt water Tonicity Hypotonic Hypertonic Blood volume Increased Decreased Mechanism Ventricular fibrillation Pulmonary oedema Time to death 4–5 min 8–12 min Applied
- These classical distinctions are based on animal experiments; in humans the differences are much less clear-cut because aspirated volumes are small
- Management of both is essentially the same — oxygenation and supportive care
🔑KEY POINTS TO REMEMBER- Fresh water is hypotonic → haemodilution, haemolysis, hyperkalaemia, ventricular fibrillation.
- Salt water is hypertonic → haemoconcentration and pulmonary oedema.
- Death is faster in fresh water; in humans the distinction is less marked.
📚SOURCES: The Essentials of Forensic Medicine and Toxicology (K.S. Narayan Reddy); Textbook of Forensic Medicine and Toxicology (V.V. Pillay); Modi’s Textbook of Medical Jurisprudence and Toxicology.