What are the possible causes of thick black‑brown patches on the grayish skin surrounding a chest tattoo in a corpse?

Postmortem Skin Discoloration Around Tattoos on a Corpse

The thick blackish spots on grayish skin around a chest tattoo in a corpse are most likely postmortem decomposition pigments that obscure the underlying tattoo, though differential considerations include postmortem blood extravasation, pre-existing infectious complications, or tattoo pigment migration.

Primary Consideration: Decomposition Changes

Postmortem decomposition produces dark red-black pigments that accumulate in the skin and subcutaneous tissues, creating thick discolorations that can completely obscure tattoo designs. 1

• The accumulation of decompositional pigments is a normal postmortem process that creates dark patches, particularly prominent around areas with existing pigmentation like tattoos 1
• These decomposition products can be temporarily removed with 3% hydrogen peroxide to reveal underlying tattoos for identification purposes 1
• Infrared reflectography demonstrates that skin discoloration from decomposition greatly affects conventional photography but does not obscure tattoos when using infrared imaging techniques 2
• Decomposition changes including partial mummification and skin discoloration occur progressively, with discoloration significantly impacting visual appearance within days 2

Secondary Consideration: Postmortem Blood Extravasation

Postmortem extravasation of blood can create bruise-like discolorations that appear as dark patches, particularly in dependent body positions or after body manipulation. 3

• Florid postmortem blood extravasation can simulate antemortem bruising and create considerable apparent discoloration 3
• The degree of extravasation relates to loose subcutaneous tissues (particularly in head/neck/chest regions), dependent body position, and any postmortem trauma 3
• Thumb-sized or larger discolorations resembling bruising can appear postmortem, especially when bodies are grasped or moved 4
• These discolorations can be significant in size and may be mistaken for antemortem injuries 4

Antemortem Pathology Considerations

Infectious Complications

If the tattoo was recent or the individual died from sepsis, consider pre-existing tattoo-related infections:

• Pyogenic infections (Staphylococcus aureus, Streptococcus pyogenes) can cause cellulitis, pustules, or abscesses with surrounding inflammation and discoloration 5, 6
• Nontuberculous mycobacterial infections (M. chelonae, M. abscessus) can cause severe abscesses with surrounding tissue changes, requiring 4+ weeks to develop 5, 6
• Necrotizing fasciitis presents with skin necrosis, ecchymoses, and bullous lesions with a "hard, wooden feel" extending beyond visible involvement, though this would show characteristic tissue destruction at autopsy 5

Tattoo Pigment-Related Changes

• Tattoo inks contain metal salts including iron, mercury, chromium, cobalt, and titanium that can create dark pigmentation 5
• Black tattoo pigments may contain charcoal powder or other dark materials that could appear as thick spots if there was pigment migration or inflammatory reaction 5
• Histopathologic reactions to tattoo pigments can include various immune-mediated responses, though these typically occur antemortem 7

Diagnostic Approach

To differentiate these possibilities:

1. Apply 3% hydrogen peroxide to the affected area - decomposition pigments will temporarily clear, revealing underlying tattoo 1
2. Use infrared reflectography - decomposition discoloration becomes insignificant while tattoo and other features remain visible 2
3. Assess distribution pattern - decomposition pigments diffusely obscure tattoos; blood extravasation follows gravity/dependent areas; infections would show localized inflammatory changes 3, 1
4. Examine tissue planes at autopsy - necrotizing infections show characteristic fascial involvement with gray, swollen fascia and brownish exudate 5

Critical Pitfall

Do not assume all dark discoloration around tattoos on corpses represents antemortem pathology - postmortem changes are the most common explanation and can be dramatic in appearance, potentially leading to incorrect conclusions about cause or manner of death 3, 4.