Dermatome Painting Session
A dermatome is defined as the cutaneous area supplied by one spinal nerve,
through both rami (Standring et al., 2005). An alternative kind of explanation is
that it is the tissue derived from the dermamyotome component of one somite
in the embryo(Anthoney, 1994).
Dermatomes are a clinically important concept in human anatomy highly
relevant to your future clinical practice. Knowledge of the dermatomal
distribution of referred pain from visceral disease is essential to diagnosis.
Familiarity with dermatome distributions is also essential in testing to
determine sensory limits in regional anaesthesia, such as before a Caesarean
section. They are key to determining the level of spinal cord injury or
pathology. However despite this, a recent unpublished study has observed
significant variation between published maps, with 14 different versions found
in 13 different textbooks (Gray’s Anatomy 39th Edition has two different
maps!). Even accounts of the development of the dermatome pattern are
fanciful in nature (McLachlan, 1990).
The original sources of most maps are Foerster 1933 and Keegan and Garret
1948, although inadequate referencing in anatomy textbooks may conceal
this. Foerster’s map was derived by mapping the area of sensation that
remained after sectioning the nerve roots above and below a single root.
Kegan and Garret studied pain distributions in patients about to undergo
surgery. Another important account came from Head and Campbell, 1900,
who mapped skin lesions in patients with Herpes zoster. These and other
studies have been combined in various ways to give the variety of maps
observed in textbooks.
Key messages to be borne in mind when viewing dermatome maps are as
follows.
1) Dermatome distributions are variable from individual to individual.
Published maps are ‘average’ values and may not describe any one
person
2) There is considerable overlap between dermatomes, which the
conventional ‘zebra stripe’ representation does not adequately reflect
3) Different ways of determining nerve distribution may give different
results (e.g. shingles rashes may not match sensory nerve distribution)
In this pilot practical session, we are aiming to discover
a) how long it takes to identify the clinical landmarks on the body that
enable a dermatome map to be identified
b) How long it takes to paint dermatome maps once the landmarks have
been identified
c) which colours are most suitable for dermatome mapping
d) how the overlap between dermatomes can best be represented
e) How the ‘fuzziness’ of dermatomes can best be represented
f) Explore the visual impact of dermatome models with a view to
contributing to a science and art project.
As part of the pilot process, we would like to be able to take photographs at
various stages of the process and we will ask you if you are happy for these
photographs to be used in academic presentations. They will not be used in
public presentations, or made available on line or through any other open
access media.
Activities
Tasks will be carried out in 3 pairs. Each pair should tackle one of the
following:
1. painting the dermatomes on the thorax, alternating dermatomes from
side to side, and representing the expansion of each dermatome
beyond its conventional distribution.
2. painting the dermatomes on the upper limbs, alternating dermatomes
from side to side, and representing the expansion of each dermatome
beyond its conventional distribution.
3. painting the dermatomes on the lower limbs, alternating dermatomes
from side to side, and representing the expansion of each dermatome
beyond its conventional distribution.
References
Anthoney TR. 1994. Neuroanatomy and the neurologic exam: a thesaurus of
synonyms, similar sounding non-synonyms, and terms of variable meaning.
BocaRaton: CRC Press. p185-189.
Foerster O. 1933. The dermatomes in man. Brain 56:1-39.
Head H, Campbell AW. 1900. The pathology of herpes zoster and its bearing
on sensory localisation. Brain 23:353-523.
Keegan JJ, Garrett FD. 1948. The segmental distribution of the cutaneous
nerves in the limbs of man. Anat Rec 102:409-437
McLachlan JC. 1990. Development of the dermatome pattern in the limb. Clin
Anat 3:41-49.
Standring S, Ellis H, Healy JC, Williams A, et al (eds). 2005. Gray's Anatomy:
The Anatomical Basis of Clinical Practice, 39th Ed. Philadelphia:
Elsevier/Churchill Livingstone. p 175, 734, 1413.