Dermatome (anatomy)
Dermatome | |
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![]() Dermatomes of the Upper and Lower Limbs (Modified, after Keegan, J. J., and Garrett, F. D.) | |
![]() Dermatomes of the Upper Parts of the Body, displaying significant overlapping (Modified, from Fender, after Foerster) | |
Anatomical terminology |
A dermatome is an area of skin that is mainly supplied by a single spinal nerve.[1] There are 8 cervical nerves (C1 being an exception with no dermatome), 12 thoracic nerves, 5 lumbar nerves and 5 sacral nerves. Each of these nerves relays sensation (including pain) from a particular region of skin to the brain.
A dermatome also refers to the part of an embryonic somite.
Along the thorax and abdomen the dermatomes are like a stack of discs forming a human, each supplied by a different spinal nerve. Along the arms and the legs, the pattern is different: the dermatomes run longitudinally along the limbs. Although the general pattern is similar in all people, the precise areas of innervation are as unique to an individual as fingerprints.
A similar area innervated by peripheral nerves is called a peripheral nerve field.
Clinical significance
![](http://upload.wikimedia.org/wikipedia/commons/thumb/a/a4/1506_Referred_Pain_Chart.jpg/220px-1506_Referred_Pain_Chart.jpg)
A dermatome is an area of skin supplied by sensory neurons that arise from a spinal nerve ganglion. Symptoms that follow a dermatome (e.g. like pain or a rash) may indicate a pathology that involves the related nerve root. Examples include somatic dysfunction of the spine or viral infection. Referred pain usually involves a specific, "referred" location so is not associated with a dermatome.
Viruses that lie dormant in nerve ganglia (e.g. varicella zoster virus, which causes both chickenpox and herpes zoster commonly shingles), often cause either pain, rash or both in a pattern defined by a dermatome. However, the symptoms may not appear across the entire dermatome.
Important dermatomes and anatomical landmarks
Following is a list of spinal nerves and points that are characteristically belonging to the dermatome of each nerve:[2]
![](http://upload.wikimedia.org/wikipedia/commons/thumb/6/6f/Grant_1962_665.png/250px-Grant_1962_665.png)
- C2 - At least one cm lateral to the occipital protuberance at the base of the skull. Alternately, a point at least 3 cm behind the ear.
- C3 - In the supraclavicular fossa, at the midclavicular line.
- C4 - Over the acromioclavicular joint.
- C5 - On the lateral (radial) side of the antecubital fossa, just proximally to the elbow.
- C6 - On the dorsal surface of the proximal phalanx of the thumb.
- C7 - On the dorsal surface of the proximal phalanx of the middle finger.
- C8 - On the dorsal surface of the proximal phalanx of the little finger.
- T1 - On the medial (ulnar) side of the antecubital fossa, just proximally to the medial epicondyle of the humerus.
- T2 - At the apex of the axilla.
- T3 - Intersection of the midclavicular line and the third intercostal space
- T4 - Intersection of the midclavicular line and the fourth intercostal space, located at the level of the nipples.
- T5 - Intersection of the midclavicular line and the fifth intercostal space, horizontally located midway between the level of the nipples and the level of the xiphoid process.
- T6 - Intersection of the midclavicular line and the horizontal level of the xiphoid process.
- T7 - Intersection of the midclavicular line and the horizontal level at one quarter the distance between the level of the xiphoid process and the level of the umbilicus.
- T8 - Intersection of the midclavicular line and the horizontal level at one half the distance between the level of the xiphoid process and the level of the umbilicus.
- T9 - Intersection of the midclavicular line and the horizontal level at three quarters of the distance between the level of the xiphoid process and the level of the umbilicus.
- T10 - Intersection of the midclavicular line, at the horizontal level of the umbilicus.
- T11 - Intersection of the midclavicular line, at the horizontal level midway between the level of the umbilicus and the inguinal ligament.
- T12 - Intersection of the midclavicular line and the midpoint of the inguinal ligament.
- L1 - Midway between the key sensory points for T12 and L2.
- L2 - On the anterior medial thigh, at the midpoint of a line connecting the midpoint of the inguinal ligament and the medial epicondyle of the femur.
- L3 - At the medial epicondyle of the femur.
- L4 - Over the medial malleolus.
- L5 - On the dorsum of the foot at the third metatarsophalangeal joint.
- S1 - On the lateral aspect of the calcaneus.
- S2 - At the midpoint of the popliteal fossa.
- S3 - Over the tuberosity of the ischium or infragluteal fold
- S4 and S5 - In the perianal area, less than one cm lateral to the mucocutaneous zone
Additional images
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Diagram of segmental distribution of the cutaneous nerves of the right upper extremity.
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Lower limb.
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Foot.
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Major dermatomes and cutaneous nerves (anterior view).
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Major dermatomes and cutaneous nerves. (posterior view).
See also
References
- ^ "Dermatomes Anatomy". eMedicine. Retrieved 10/9/2013.
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(help) - ^ Key Sensory Points from International Standards for the Classification of Spinal Cord Injury. June 200
External links
![](http://upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/30px-Commons-logo.svg.png)
- 3D Dermatomes Web App, Instamedic
- Hand kinesiology at the University of Kansas Medical Center
- Diagram "Adult Dermatome", The New York Times