The T9 dermatome is a band that wraps around the trunk over the upper abdomen just above the umbilicus. Like other thoracic dermatomes, it slopes slightly downward from the back to the front. Its skin is supplied by the ninth intercostal nerve through its lateral and anterior cutaneous branches.
| Nerve root | T9 |
|---|---|
| Area | Band around the trunk over the upper abdomen just above the umbilicus |
| How to test | Light touch and pinprick are compared side to side at the ISNCSCI key sensory point: in the midclavicular line midway between the T8 and T10 points. |
| Nerve Supply | Ninth intercostal nerve (lateral and anterior cutaneous branches); Posterior rami of thoracic spinal nerves |
Carries touch, pain and temperature sensation from this strip of skin to the spinal cord through the T9 dorsal root.
Abdominal wall pain in this band can come from the thoracic root or the intercostal nerve rather than an abdominal organ, for example in shingles before the rash appears, diabetic thoracic radiculopathy or anterior cutaneous nerve entrapment. Visceral pain from upper abdominal organs is also referred to roughly the T6-T9 levels. 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 T9 dorsal root ganglion causes a painful band of blistering rash confined to this dermatome, sometimes followed by postherpetic neuralgia.
A diabetic nerve root disorder that causes burning band-like pain and numbness across the trunk, sometimes with bulging of the abdominal wall.
Trapping of an anterior cutaneous branch where it passes through the rectus sheath causes sharp, localised abdominal wall pain.
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