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CHAPTER 24
horn area, while those for the sacral segments are situated closest to the dorsal medium
septum. In the cervical cord, there is also a clear division of the posterior column into
two parts demarcated by the posterior intermediate sulcus. The medial part, fasciculus
gracilis (Goll's tract), is composed of the long posterior root fibres for the lower part of
the body (T4 and below), while the lateral part, fasciculus cuneatus (Burdach's tract),
contains the fibres for the upper parts of the body (from T3 upwards). There is also
some segregation of the various modalities of posterior column sensibility (pressure,
vibration, position sense, kinaesthesia, touch). The predominant symptom of posterior
column involvement is ataxia, resulting in a positive Romberg's sign, if the disturbance
of postural sensibility affects both lower limbs. Knowledge of these anatomical arrange
ments, as shown schematically in Fig. 113, facilitates the understanding of the dissocia
tions in the clinical symptomatology of incomplete lesions of the spinal cord. All this
explains the often irregular and dissociated disturbances of sensibility in the later stages of
incomplete and in particular recovering cervical lesions (Fig. 132). This applies not only
to dissociation between pain and temperature sensibility but also to pain, tickling and
libidinous sensations and the various components of postural sensibility. In lesions with
interruption of the spino-thalamic tracts, the sensation of vibration, which is mediated
by the posterior column tract, is intact but the accompanying tickling sensation conducted
by the spino-thalamic tract is abolished. Moreover, it may be stressed that immediately
after injury certain types of sensibility may be spared in areas below the level of the
lesion, even in only a few dermatomes, which allows the correct diagnosis at once. Such
sparing occurs not infrequently in the lower sacral segment in incomplete lesions of the
cervical cord. Therefore, repeated sensory tests—preferably by the same investigator—
in the state of spinal shock and in the early days and weeks after injury are essential.
Sensory disturbances in lesions of posterior spinal roots
The area innervated by a single posterior root is termed dermatome. Detailed studies
have been carried out in the past in animals and man, following resection of single
posterior roots (Sherrington, 1898; Foerster, 1933, 1936; Keegan, 1943), by clinical
observations in herpes zoster or afflictions of internal organs (Head, 1893, I 9OI )j strych-
ninization of the root entry zone in the cat (Dusser de Barenne, 1935), vasodilatation
following electrical stimulation of the peripheral end of a divided posterior root (Bayliss,
1901; Foerster, 1933, I 936)3 and hyperaesthesia induced by injection of 5 per cent or
6 per cent saline solution (Kellgren, 1939; Lewis, 1942). As a result, charts of a derma-
tomal pattern of the whole body have been mapped out by various authors, the most
well known are those of Head (Fig. 1143) and Foerster (Fig. ii4b). While giving a rough
orientation of the metameric cutaneous arrangement and being sufficient for clinical
diagnosis, they do not give details of the true distribution of individual posterior roots
and their overlap with their neighbours, nor do they show the different areas of distri
bution of the various modalities of sensibility, in particular the relationship of the areas
of anaesthesia and analgesia. Although following resection of a single posterior root in
man, especially in the thoracic area, there is an immediate sensory loss for all qualities,
the area of sensory loss will shrink and altogether disappear within a very short time, not
