Dermatomen

Dermatomen are anatomical skin regions that are innervated by sensory fibers from a single spinal nerve. Each dermatome corresponds to the sensory distribution of a dorsal root from a spinal segment, forming a segmental map of the body’s surface. There are 31 spinal nerves—8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal—each contributing to one or more dermatomes. In practice, the dermatomal map is an approximate representation; there is considerable overlap between adjacent dermatomes, which provides some redundancy for sensation if a single nerve is damaged.

Dermatomes are most easily observed on the trunk as broad, horizontal bands and on the limbs with more variable patterns shaped by nerve plexuses. Clinically, dermatomen are used to localize lesions along the spinal cord or nerve roots. Loss or alteration of sensation within a specific dermatome can indicate radiculopathy, while a rash restricted to a dermatomal pattern strongly suggests herpes zoster (shingles). Dermatomal information also aids in planning regional anesthesia and in interpreting neurological exams to distinguish peripheral nerve injury from more central causes.

The face is an important exception: it is innervated by the trigeminal nerve rather than spinal dermatomes, and has its own facial dermatomal distribution. Dermatomal maps are useful tools in neurology, dermatology, and anesthesiology, but individual variability and overlap mean the maps are approximate guides rather than precise boundaries.