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
A firearm is a weapon that discharges a projectile by the force of expanding gases; firearm injuries are the wounds so produced.
Classification of Firearms
- Rifled (small-bore) — spiral grooves in the barrel impart spin to a single bullet: revolver, pistol, rifle
- Smooth-bore (shotgun) — no grooves; fires multiple pellets
- Automatic and semi-automatic weapons
- Country-made (improvised) weapons — common in India
- Rifling leaves class and individual characteristics on the bullet, allowing weapon identification
Types of Firearm Injury
- Penetrating — projectile enters but does not exit; bullet recovered
- Perforating (through-and-through) — both entry and exit wounds
- Grazing — tangential, superficial furrow
- Ricochet — deflected projectile; irregular, larger wound with unstable flight
- Tandem (piggyback) — two bullets together
- Injury also from flame, gases, unburnt powder and wad at close range
Wound features depend on the projectile and on what accompanies it. Weapon Projectile Rifled Single bullet Shotgun Multiple pellets Ricochet Deflected, irregular Applied
- Recovered bullets are handled with gloved fingers or rubber-tipped forceps to preserve markings
- Radiograph the body to locate retained projectiles before dissection
🔑KEY POINTS TO REMEMBER- Firearms are rifled (single bullet) or smooth-bore (multiple pellets).
- Injuries: penetrating, perforating, grazing, ricochet and tandem.
- Rifling marks on the bullet permit weapon identification.
📚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
Distinguishing the entrance from the exit wound is fundamental to reconstructing the direction of fire and the position of the assailant.
Entrance Wound
- Usually smaller and round or oval, with inverted margins
- Abrasion (contusion) collar — a ring of abraded skin, characteristic
- Grease (dirt) collar — lubricant and dirt wiped from the bullet
- Blackening, tattooing and singeing if fired from close range
- In flat bones of the skull, the inner table is bevelled (cone widens inwards)
Exit Wound
- Usually larger and irregular, stellate or slit-like, with everted margins
- No abrasion or grease collar; no blackening or tattooing
- May be absent (penetrating wound) or multiple (bullet fragmentation)
- In the skull the outer table is bevelled (cone widens outwards)
- Shored exit wound — if skin is supported by clothing or a wall, the margin may be abraded and mimic an entry
The abrasion collar is the single most reliable sign of an entry wound. Feature Entry Exit Size Smaller Larger Margins Inverted Everted Abrasion collar Present Absent Skull bevelling Inner table Outer table Applied
- Beware the shored exit wound, which can be mistaken for an entry
- Never describe wounds as ‘entry’ or ‘exit’ until all features are assessed
🔑KEY POINTS TO REMEMBER- Entry wound: small, inverted margins, abrasion and grease collar.
- Exit wound: larger, everted, irregular, without collars.
- Skull shows internal bevelling at entry and external bevelling at exit.
📚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
Range of fire is the distance between the muzzle and the victim, estimated from the pattern of flame, gas, soot and powder around the entry wound.
Rifled Weapon Ranges
- Contact — muzzle against skin: muzzle imprint, cruciate/stellate wound over bone, soot and gases inside the track, cherry-red carboxyhaemoglobin discoloration
- Close (near contact, within a few cm) — singeing (burning) of hair and skin, dense blackening
- Intermediate — tattooing (stippling) from unburnt powder grains, up to about 60–75 cm
- Distant — only the bullet reaches: entry wound with abrasion collar, but no blackening, tattooing or singeing
Key Signs and Their Limits
- Flame (singeing) — up to about 15 cm
- Smoke (blackening) — up to about 30 cm; washable
- Unburnt powder (tattooing) — up to about 60–75 cm; not washable — a vital sign
- Beyond this only the projectile causes injury
- Test firing with the same weapon and ammunition gives the most accurate estimate
Each component travels a different distance, marking the range. Sign Range Singeing Up to ~15 cm Blackening Up to ~30 cm Tattooing Up to ~60–75 cm Applied
- Tattooing cannot be washed off — distinguishes it from blackening
- A contact wound over bone gives the classic stellate tear from gas expansion
🔑KEY POINTS TO REMEMBER- Range assessed from singeing, blackening and tattooing around the entry wound.
- Singeing ~15 cm, blackening ~30 cm, tattooing ~60–75 cm.
- Distant shots show only the bullet wound with an abrasion collar.
📚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
Head injury is trauma to the scalp, skull or brain, and is the commonest cause of death in road traffic accidents and assaults.
Scalp and Skull Injuries
- Scalp: abrasion, contusion, laceration, avulsion
- Fissured (linear) fracture — commonest; depressed fracture — localised heavy blow, may reproduce the weapon
- Comminuted, gutter and ring fracture (around foramen magnum, from a fall on the feet or vertex)
- Contrecoup fracture; hinge fracture of the base
- Pond fracture — in infants, from the elastic skull
Intracranial Haemorrhage
- Extradural — middle meningeal artery tear with temporal bone fracture; lucid interval; biconvex (lentiform) on CT
- Subdural — tear of bridging veins; common in the elderly and alcoholics; may be chronic; crescentic on CT
- Subarachnoid — trauma or ruptured berry aneurysm
- Intracerebral — contusion, laceration
- Coup — injury at the site of impact; contrecoup — opposite side, typical of a fall on a moving head
Contrecoup injury suggests a fall; coup injury suggests a blow. Haemorrhage Vessel CT shape Extradural Middle meningeal artery Biconvex Subdural Bridging veins Crescentic Subarachnoid Aneurysm/trauma Diffuse Applied
- Lucid interval is characteristic of extradural haemorrhage
- Diffuse axonal injury causes prolonged coma with little visible damage
🔑KEY POINTS TO REMEMBER- Fissured fracture is commonest; depressed fracture may reproduce the weapon.
- Extradural: middle meningeal artery, lucid interval, biconvex.
- Subdural: bridging veins, crescentic; contrecoup injury suggests a fall.
📚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
Regional injuries are those affecting the spine, chest and abdomen, each with characteristic mechanisms and medicolegal significance.
Spinal Injuries
- Mechanisms: hyperflexion, hyperextension, rotation, compression
- Whiplash injury — cervical, from rear-end collision
- Fracture-dislocation commonest at the mobile cervical and thoracolumbar junctions
- Hangman’s fracture — fracture of C2 pedicles
- Cord injury → quadriplegia (above C5), paraplegia; above C4 → respiratory paralysis and death
- Spinal shock; delayed death from urinary infection and bedsores
Chest and Abdominal Injuries
- Rib fractures — direct or indirect; flail chest with paradoxical movement
- Pneumothorax, haemothorax, cardiac tamponade, aortic rupture (deceleration, at the isthmus)
- Commotio cordis — fatal arrhythmia from a blow to the precordium
- Abdomen: liver and spleen most commonly injured; ruptured spleen may bleed late (delayed rupture)
- Blunt abdominal trauma may show no external mark despite fatal internal injury
- Hollow viscus rupture → peritonitis; retroperitoneal haemorrhage
Absence of external injury never excludes fatal internal damage. Region Common injury Spine Fracture-dislocation Chest Rib fracture, tamponade Abdomen Liver, spleen rupture Applied
- A blow to the epigastrium may cause vagal inhibition and instant death
- Delayed splenic rupture may follow apparently trivial trauma
🔑KEY POINTS TO REMEMBER- Spinal injury above C4 causes respiratory paralysis and death.
- Chest: flail chest, tamponade, aortic rupture at the isthmus.
- Liver and spleen are most often injured; external marks may be absent.
📚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
Shotgun injuries are produced by smooth-bore weapons discharging multiple pellets, with wound features that vary greatly with range.
Wound Pattern by Range
- Contact / very close (<30 cm) — single large circular hole with charred, blackened margins; wad enters the wound
- Close (30 cm–1 m) — single hole with scalloped (rat-hole/cribriform) margins from beginning pellet spread
- Intermediate (1–3 m) — central hole surrounded by satellite pellet holes
- Distant (>3 m) — separate individual pellet wounds, no central defect
- Rule of thumb: pellet spread in inches ≈ range in yards minus one
Other Features
- Exit wounds are usually absent — pellets lack the energy to leave the body
- The wad is important — its presence indicates close range; its recovery may identify the cartridge
- Massive local tissue destruction at close range
- Billiard-ball ricochet of pellets within the body
- Radiography shows the pellet distribution
Pellet dispersion widens predictably with distance, allowing range estimation. Range Wound <30 cm Single large hole 1–3 m Central + satellite holes >3 m Separate pellet wounds Applied
- Always recover and preserve the wad and pellets
- Test firing with the same weapon gives the most accurate range
🔑KEY POINTS TO REMEMBER- Close range gives a single large hole; distant range gives separate pellet wounds.
- Presence of the wad in the wound indicates close range.
- Exit wounds are usually absent in shotgun injuries.
📚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
Blast injuries result from the sudden release of energy in an explosion, causing injury through pressure waves, fragments, displacement and burns.
Classification
- Primary — blast (pressure) wave acting on air-containing organs: ruptured tympanic membrane (most sensitive), blast lung, bowel perforation
- Secondary — flying fragments and debris; commonest cause of injury and death; penetrating and lacerated wounds
- Tertiary — victim thrown against objects; blunt trauma, fractures, head injury
- Quaternary — burns, inhalation of gases and dust, crush injury from building collapse, psychological effects
Features & Medicolegal Aspects
- Blast lung — pulmonary contusion, haemorrhage and oedema; the commonest fatal primary injury
- Air embolism from alveolar rupture
- Body may be fragmented near the centre of the explosion
- Identification often requires DNA and dental comparison
- Collect clothing, fragments and residues for explosive analysis
- Position of the victim may be reconstructed from injury pattern
Fragments, not the pressure wave, cause most casualties. Type Mechanism Primary Pressure wave Secondary Fragments Tertiary Body thrown Applied
- Ruptured eardrum is a marker of significant blast exposure
- Mass casualty identification depends on DNA and dental records
🔑KEY POINTS TO REMEMBER- Four categories: primary (pressure), secondary (fragments), tertiary (displacement), quaternary.
- Blast lung and ruptured tympanic membrane are the key primary injuries.
- Secondary fragment injuries cause most deaths; identification needs DNA.
📚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
Road traffic accident injuries are injuries sustained by pedestrians, occupants and riders in vehicular collisions, with characteristic patterns.
Pedestrian Injuries
- Primary impact — bumper injury; fracture of tibia and fibula; height indicates the vehicle type and whether it was braking
- Secondary impact — body thrown onto the bonnet or windscreen; head and chest injuries
- Secondary (tertiary) injuries — from falling onto the road; abrasions and head injury
- Crush (run-over) injuries — tyre-mark imprint abrasion, flaying of skin, degloving
- ‘Bumper fracture’ is wedge-shaped, its base indicating the direction of impact
Occupant & Rider Injuries
- Driver — steering wheel injury to chest, dicing injuries from windscreen glass, dashboard injuries to knees and hip
- Seat-belt marks across the chest and abdomen — indicate who was driving
- Whiplash injury of the neck in rear-end collisions
- Two-wheeler riders — head injury commonest cause of death; helmet use decisive
- Alcohol is a major contributing factor — preserve blood for estimation
The sequence of impacts creates a recognisable pattern of injuries. Injury Indicates Bumper fracture Vehicle height, direction Seat-belt mark Occupant position Dicing injury Windscreen glass Applied
- Seat-belt marks and dicing injuries help identify the driver
- Preserve clothing and paint fragments for vehicle matching
🔑KEY POINTS TO REMEMBER- Pedestrian: primary bumper fracture, secondary bonnet impact, then road fall.
- Bumper fracture height indicates the vehicle type and direction.
- Seat-belt marks and dicing injuries help establish who was driving.
📚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
Cerebral concussion (commotio cerebri) is a transient, reversible loss of consciousness following head injury, without demonstrable structural damage.
Mechanism & Features
- Sudden acceleration-deceleration or rotational movement of the brain
- Transient disturbance of the reticular activating system
- Immediate loss of consciousness, usually brief (seconds to minutes)
- Retrograde amnesia — for events before the injury; anterograde amnesia for events after
- Headache, dizziness, nausea, vomiting, confusion on recovery
- No macroscopic lesion at autopsy — a functional disturbance
Complications & Medicolegal Importance
- Post-concussion syndrome — headache, poor concentration, irritability, insomnia lasting weeks to months
- Second impact syndrome — catastrophic swelling after a repeat injury
- Repeated concussion → chronic traumatic encephalopathy (‘punch-drunk’ syndrome in boxers)
- The person may perform purposeful acts during the amnesic period — relevant to responsibility
- Automatism may be pleaded as a defence
- Concussion may be feigned for compensation
The disturbance is functional, which is why autopsy shows nothing. Feature Detail Structural damage Absent Amnesia Retrograde + anterograde Late effect Post-concussion syndrome Applied
- Extent of retrograde amnesia roughly reflects severity
- Observe for delayed extradural haemorrhage after apparent recovery
🔑KEY POINTS TO REMEMBER- Concussion is transient loss of consciousness with no structural damage.
- Retrograde and anterograde amnesia are characteristic.
- Repeated concussion causes chronic traumatic encephalopathy.
📚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
Whiplash injury is a hyperextension-hyperflexion injury of the cervical spine, classically caused by a rear-end vehicle collision.
Mechanism
- Vehicle struck from behind → trunk thrust forward while the head lags
- Sudden hyperextension of the neck, followed by rebound hyperflexion
- Damage to anterior longitudinal ligament, muscles, intervertebral discs and facet joints
- May cause cervical vertebral fracture, disc prolapse and, in severe cases, cord or brainstem injury
- Worse without a properly adjusted head restraint
Features & Medicolegal Importance
- Delayed onset — pain and stiffness typically appear 12–24 hours later
- Neck pain, restricted movement, headache, dizziness, paraesthesia of the arms
- Radiographs are often normal — MRI may show soft-tissue injury
- Frequent subject of compensation claims, and commonly exaggerated or malingered
- Symptoms may persist for months (‘whiplash-associated disorder’)
- Severe cases may cause instant death from brainstem injury
The delay between injury and symptoms is characteristic. Feature Detail Mechanism Hyperextension then flexion Onset 12–24 hours X-ray Often normal Applied
- Head restraints markedly reduce the severity of whiplash
- Document objective findings carefully because of compensation disputes
🔑KEY POINTS TO REMEMBER- Whiplash is cervical hyperextension followed by hyperflexion in rear-end collisions.
- Pain and stiffness appear after 12–24 hours; X-rays are often normal.
- Commonly involved in compensation claims and may be exaggerated.
📚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
Firearm residue is the material deposited on the hands and clothing of a person who has discharged a firearm, and helps establish whether a person fired a weapon.
Nature and Detection
- Residue contains partially burnt and unburnt propellant, soot, and primer metals — lead, barium and antimony
- Dermal nitrate (paraffin/diphenylamine) test — warm paraffin cast of the hand, treated with diphenylamine reagent; blue specks indicate nitrites
- Highly non-specific — fertilisers, tobacco, urine, cosmetics and matches also give positive results; now largely obsolete
- Modern methods: atomic absorption spectrophotometry, scanning electron microscopy with energy-dispersive X-ray — detects characteristic spheroidal particles containing all three primer metals
Collection & Interpretation
- Swabs or adhesive stubs taken from the back of the hand, web space and thumb
- Collect as early as possible — residue is lost by washing, wiping and normal activity within hours
- Also collect the clothing and a control sample
- A positive result does not prove firing — may follow handling a weapon or being near a discharge
- A negative result does not exclude firing
- Must be interpreted alongside wound findings and the scene
SEM-EDX identifying lead, barium and antimony together is the reliable test. Test Value Dermal nitrate Obsolete, non-specific AAS Detects metals SEM-EDX Most specific Applied
- Bag the hands of the deceased at the scene to preserve residue
- Interpret cautiously — residue evidence is corroborative only
🔑KEY POINTS TO REMEMBER- Firearm residue contains lead, barium and antimony from the primer.
- The dermal nitrate test is non-specific and now obsolete.
- SEM-EDX is the most specific method; results are corroborative only.
📚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
Country-made (improvised or ‘katta’) firearms are crudely manufactured unlicensed weapons, encountered frequently in Indian medicolegal practice.
Forensic Characteristics
- Smooth or poorly rifled barrel — bullets carry few or no reliable rifling marks, hampering weapon identification
- Poor-quality, often handloaded ammunition → incomplete powder combustion
- Results in heavy blackening and extensive tattooing even at longer ranges than expected
- Range estimation is unreliable — standard distance tables do not apply
- Low and inconsistent muzzle velocity → bullets often lodge in the body (penetrating rather than perforating wounds)
- Irregular projectiles cause atypical, irregular entry wounds
Medicolegal Importance
- Common in India because they are cheap and easily obtained illegally
- Possession is an offence under the Arms Act
- Weapon may burst on firing, injuring the user — producing injuries on the hand and face of the assailant
- Test firing with the recovered weapon and similar ammunition is essential before opining on range
- The doctor should state that findings are consistent with a country-made weapon rather than being definitive
- Always recover the projectile and preserve clothing
Poor ammunition quality is why standard range estimates fail. Feature Effect Poor rifling No identifying marks Incomplete combustion Excess blackening Low velocity Bullet retained Applied
- Never apply standard range criteria to country-made weapons
- Examine the suspect for injuries from a bursting weapon
🔑KEY POINTS TO REMEMBER- Country-made firearms have poor rifling, so bullets carry few identifying marks.
- Incomplete combustion causes excess blackening and tattooing at greater distances.
- Standard range estimation is unreliable — test firing is essential.
📚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.