My study notes for forensic pathologists

1. Hazem Ali

2. Hazem Ali

3.  Low-Voltage Lines (Domestic): varies from country to country
 USA: 110 – 120 V, 60 Hz “cycles per second” (AC)
 Egypt, Europe: 220 – 240 V, 50 Hz (AC)
 High-Voltage Lines
 1ry distribution power lines: up to 20,000 V
 High tension power lines (towers): up to 100,000 V
 Industrial:
 Very high voltage: up to 400,000 V
 Natural:
 Lightning

4.  Direct current (DC):
 Flows constantly in the same direction
 Less commonly used (some industries)
 Alternating current (AC):
 reverses its direction at regular intervals
 Commonly used in household devices
 Why AC is more dangerous than DC?
 More commonly used (more accidents)
 More risk for muscle spasm “hold-on” and cardiac arrhythmia
 The danger to the body exists when the rate lies between 40 and 150 Hz “cycles
per second”
 An increase/decrease in rate above/below this range decreases the danger.
 E.g. at 1720 cps the heart is 20 times less likely to fibrillate than at 150 cps

5. 𝑰 =
𝑽
𝑹
 (I) amount of current flow
 (V) electromotive force
 (R) resistance to the conduction of electricity

6. Amperage (Current):
 The actual amount of electricity flow (number of electrons per unit
time)
 Current is the most important factor in electrocution:
 A current of high voltage with low amperage can be less dangerous than one with
moderate voltage but high amperage
 Factors affecting amperage:
 Voltage (direct relation)
 Resistance of the tissue (inverse relation)
 Time for which the current is flowing (affects degree of tissue damage)

7. Amperage (Current):
 Current of 1 mA  tingling sensations
 Current of 5 mA  muscle tremors
 Current of 8-20 mA  muscular spasm “hold-on”
 Current around 40 mA  loss of consciousness
 Current of 75-100 mA  ventricular fibrillation
 Current above 1 ,000 mA (1 A)  cardiac arrest
 In this case, the heart should start beating normally after the circuit is broken (provided
no irreversible damages occurred to the heart)
 Current above 4 A is used to arrests ventricular fibrillation “defibrillator”

8. Voltage (Tension):
 The “Force” required to produce 1 ampere of intensity when passed
through a conductor having the resistance of 1 ohm
 Most fatalities follow shocks from currents of 220–250 V, which is the
usual range of household supply
 Low voltage (below 50 V) usually non-fatal
 Voltage below 500 V  muscular spasm and “hold-on” effect
 Voltage above 500 V  severe muscular contractions that throw the
victim away

9. Duration of Contact:
 The longer the contact, the greater will be the damage
 Low-amperage current needs longer time (i.e. minutes) to be lethal
 By respiratory muscle spasm
 High-amperage current needs shorter time (i.e. seconds) to be lethal
 By ventricular fibrillation

10. Resistance of tissues:
 The major barrier to the electric current is the skin
 The blood vessels in the dermis serves as a favorable medium for the
passage of current
 filled with electrolyte rich fluid
 Factors affecting resistance of skin:
 Thickness of the keratin-covered epidermis:
 palms and soles are more resistant than thin skin
 Dryness of skin:
 dry hands/feet can offer up to 1 million ohms of resistance
 Wet skin (from sweating or external moisture) offers 1000 ohms or less
 Area of contact

11. Area of Contact of the Body:
 The smaller area of contact between the skin and the electric supply
will exert more resistance than the larger area
 Tip of dry finger > palm of wet hand > wet body in a bath
 Passage of a current through a localized area of contact also generate
sufficient heat to burn the skin
 This is why electrocution in a bathtub may occur without any external mark
 The current passage through vital organs (e.g. heart, brain) is more
dangerous

12.  The current tends to run from the point of contact to the point of grounding,
following the shortest path, not necessarily the path of least resistance
 Common entry site: hand
 Common exit site: foot, other hand
 1ry causes of death:
 Ventricular fibrillation (most common)
 Spasm of the respiratory muscles
 Paralysis of the brainstem centers
 2ry causes of death:
 Head/Body injuries from falling from height
 Complications of severe burns (high-voltage lines)

13.  Ventricular fibrillation:
 When the current passes through the thorax, from hand to hand or from hand to leg
routes
 Cardiac arrest  Pallor (No cyanosis)
 Spasm of the respiratory muscles:
 When the current passing through the thorax may lead to tetanic contraction of the
muscles of respiration
 Respiratory arrest  Cyanosis (congestive hypoxia)
 Paralysis of the brainstem centers:
 when the current passes through the head (rarely when unprotected head touch the
source)
 The current can damage brainstem and leads to paralysis of cardiac and/or respiratory
centers

14.  It is very common for the individual receiving a fatal electric shock to
not lose consciousness immediately, but to yell out or state that he
just “burned” himself prior to collapse.
 This is because the brain has approximately 10–15 sec of oxygen
reserve, irrespective of the heart.
 Thus, an individual can remain conscious for 10–15 s after cessation of the heart
as a pumping organ

15.  Most common  accidental
 Rarely  suicide
 Extremely rare  homicide
 Some states in America  judicial “electric chair”

16.  Scene investigation is the key to the diagnosis of electrocution
 First step, be sure that electricity is turned off
 Victim status:
 Clothed/naked
 Simple cloths/protective gloves or shoes
 Dry/wet skin
 Points of contact with the source/ground.
 Clothes of the victim should also be described and preserved properly
 E.g. burn defects

17.  Pay attention to all electrical devices, tools, machines (especially
older or poorly maintained ones)
 Look for circuit defects
 Look for retained skin/hair of victim
 Pay attention in all work-related deaths
 Electrocution is a usual suspect
 Pay attention in all watery environment-related deaths (bathtubs,
swimming pools)
 Even if no suspicious lesions grossly

18.  In cases of cardiac arrest:
 Pallor (no cyanosis)
 In case of respiratory arrest:
 Cyanosis
 Visceral congestion
 Petechial hemorrhages
 In case of violent muscle contraction:
 Accelerated onset of rigor mortis
 Long bone fractures
 If the individuals are grasping something, they will continue to do so.

19. Entry marks:
(1) Collapsed blisters:
Mechanism:
 When firm contact to conductor
 Generated heat splits the skin layers  blister
 On cooling  collapse
Gross:
 Usually hands, fingers
 Small (few mm – 1 or 2 cm)
 Firm, Round –oval areas
 If the contact is with the long axis of the wire  linear groove
 Zones:
 Central depression ‘crater’
 Surrounded by raised edges of blanched skin
 Due to arteriolar spasm by effect of electricity
 Outermost intact skin may be mildly hyperemic

20. Entry marks:
(2) Spark nodule:
Mechanism:
 When loose contact to conductor
 the current “spark” jumps the gap between the source and the skin  melting of
keratin
 On cooling  nodule of condensed keratin
Gross:
 Usually hands, fingers
 Small (few mm – 1 or 2 cm)
 Hard, brownish nodule
 Surrounded by areola of blanched skin (due to arteriolar spasm)

21. contact blister and adjacent spark burn
In many electrical burns these two types are combined as a result of:
• Movement of the hand or body against the conductor
• Irregularity of the shape of the conductor.

22.  The strong flexion of rigor mortis may bring the fingers down to the
palms and obscure electrical marks
 So it is essential in all autopsies (when electrocution is a possibility)
to examine the flexor surface of the fingers by forcible breaking of
the rigor and even cut flexor tendons at the wrist to release the rigor
clenching of the fingers

23. Exit Marks:
 Usually feet
 Variable in appearance but usually have some of the features of entry
marks
 More tissue disruption, even skin laceration
 Burns and perforations of the clothing or shoes may be seen

24. So, is electric mark helpful and diagnostic? - NO
 Can varies in size and shape
 depending on many factors especially area of contact
 Can be absent
 If area of contact is large (as in deaths occurring in the bathtub)
 If area of contact in hidden place (as in deaths of children holding wire in their mouths)
 Can't be differentiated from thermal burn
 Can give similar gross and microscopic features
 Scanning E/M can be helpful in these cases
 Can’t differentiate ante-mortem from post-mortem injuries
 Gives the same picture (unless outside zone hyperemia)

25. High-voltage current
 Exposure:
 Direct contact
 Current “arcing” over several centimeters without real contact
 Effects:
 Multiple individual and confluent burns and charring
 High-voltage currents can produce extremely high temperature (up to 4000 C)
 Bone fractures
 Even loss of extremities or organ rupture can be seen
 “Crocodile skin” effect:
 Multiple, discrete, punched-out burns
 Dancing of current sparks over the body

26. Multiple individual and confluent burn areas
‘Crocodile skin’

27. Skin:
 Epidermis:
 Coagulative necrosis of epidermis and corium
 Separated epidermal layers from each other or from the corium
“blisters”
 Show variable sized micro-spaces in the corium and epidermis
“honeycomb appearance”
 Epidermis cells are flattened, elongated, with their nuclei become
horizontally stretched, streamed (especially basal cells)
 Blackish carbonization of the epidermis “electrical metallization”

28. Skin:
 Dermis:
 Homogenization (denaturation)
 Cells of the skin appendages may show similar damage as epidermis cells
 Subcutaneous fat:
 Fat cells in severe cases may appear to be “cooked” and display a
homogenous, golden color
ALL the previous features can be shown in thermal injuries (non-specific)
 Electron microscope and Chemical analysis can help solving these problems as it
can detect metallic deposits in electrical injuries

29.  Bubbly coagulation necrosis of the epidermis
 Blister formation

30.  Coagulative necrosis of the epidermis, with a glassy purple/pink appearance (asterisk)
 Large vacuoles (arrowhead)
 The nuclei become wavy and stretched out (arrow)

31.  Separation of the epidermis from the dermis (↑)
 Microblisters, best seen in the thick stratum corneum (→)
 Represent channels made by escaping steam.
 Dermal collagen is denatured, producing homogenous, pronounced hematoxylin staining (↓)
 Compare it with the dermal collagen on the right side of the photo.

32.  Microblisters at epidermis (arrow)
 Streaming of nuclei

33.  Microblisters in the stratum corneum
 Charring of the surface (arrow).
 Metal fragments from the point of skin contact
may be seen

34. Heart:
 Damage to Conductive system: (fatal arrhythmia)
 No Pathology (common)
 Waviness and fragmentation
 Damage to Vascular system:
 Rupture  Hemorrhage
 Spasm  Acute infarction
 Wall damage  Micro-thrombi
 Damage to Myocardium:
 Contraction bands
 Necrosis (+/- cellular reaction depending on survival time)
 Hemorrhage
Again, ALL these features are non-specific

35. Skeletal Muscle:
 Similar to cardiac muscle damage (hemorrhage, necrosis)
Lung:
 Congestion, petechial hemorrhage
 Bone marrow emboli (in cases of long bone fractures)
Kidney:
 Myoglobinuria from rhabdomyolysis
Brain:
 Congestion, petechial hemorrhage
 Axonal fragmentations
 Shrinkage of neural tissue with widening of perivascular spaces
Again, ALL these features are non-specific

36. Hazem Ali

37.  Benjamin Franklin (1706–1790) discovered that lightning flashes
were electrical discharges and not gaseous explosions
 In lightning, the discharge may be:
 From cloud to cloud
 From cloud to the earth (through tallest object in contact with earth)
 95% of lightning discharges are negative (only 5% are positive)
 Lightning chooses the path of least resistance (not the shortest)

38.  The lightning characterized by:
 Direct current
 with 20,000 amperes
 And a million volts
 Over an average period of 30 microseconds
 Lightning hits the victim by:
 Direct hit (strike)
 Indirect hit:
 Side-flash: lightning hits intermediate non-metal object (e.g. tree)
 arc to the victim (nearby one)
 Conduction: lightning hits intermediate metal object (e.g. water pipe)
 flows through it to the grounded victim (bathtub)

39.  Damaging mechanisms:
 Direct effect (strike itself)
 Burns (due to generation of huge amount of heat)
 Blast effect (due to rapidly expanding air by heat)
 Compression effect (due to return waves of air)
 Causes of death:
 Brain injury: paralysis of respiratory and/or cardiac centers
 Heart injury: arrest
 Electro-thermal injuries: burns and its complications
 Blast injuries: lacerations, fractures, and organs rupture

40.  Tearing, bursting or ripping of clothing or shoes
 Sometimes gives a false impression of criminal assault / rape
 Damage to the ground, houses, trees or animals
 Metallic objects in the area may get melted, fused
 Iron objects become magnetized
 History of thunderstorm could help solving the difficult cases

41.  Singing of the body hair
 Surface “Contact” burns:
• Due to molten or heated up metallic objects worn or carried by the victim
• Some melted metal may be implanted into the skin
 Linear burns:
 Due to current passage through area of the skin offers lesser resistance
 i.e. moist creases and folds of the skin
 Arborescent “Fern-like” burns:
 Unknown mechanism
 Seen in 1/3 of cases
• Patterned “fern-like” area of transient erythema over shoulders and flanks
• Starts after 1 hours and Fades within 24 hours if the victim survives

42. Arborescent or filigree burns

43. Blast effect:
 Severe lacerations, fractures, organs rupture
 Ruptured tympanic membranes (with blood flow from external ear)
 Can be misinterpreted as head trauma

44. Hazem Ali