The T12 dermatome is the lowest thoracic band, covering the lower abdomen just above the groin and the inguinal ligament. Its skin is supplied by the subcostal nerve, the ventral ramus of T12, with help from the iliohypogastric nerve. At the back it reaches toward the upper buttock.
| Nerve root | T12 |
|---|---|
| Area | Lower abdomen just above the inguinal ligament |
| How to test | Light touch and pinprick are compared side to side at the ISNCSCI key sensory point: in the midclavicular line at the midpoint of the inguinal ligament. |
| Nerve Supply | Subcostal nerve; Iliohypogastric nerve; Posterior rami of thoracic spinal nerves |
Carries touch, pain and temperature sensation from this strip of skin to the spinal cord through the T12 dorsal root.
The midpoint of the inguinal ligament is the ISNCSCI landmark for T12. Lower abdominal wall pain or numbness in this band after surgery, such as a hernia repair or kidney approach, may reflect injury to the subcostal or iliohypogastric nerves. Dermatome maps differ between sources (Foerster, Keegan and Garrett, and modern evidence-based maps disagree), and neighbouring dermatomes overlap, so borders are approximate.
Reactivated varicella zoster virus in the T12 dorsal root ganglion causes a painful band of blistering rash confined to this dermatome, sometimes followed by postherpetic neuralgia.
Damage during flank or lower abdominal surgery can cause numbness or pain in the lower abdomen and weakness of the lower abdominal wall.
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