124 Illustrated Textbook of Neuroanatomy
Table 10.3
Lateral Medullary Syndrome (Due to Occlusion of the Posterior Inferior Cerebellar Artery)
Sites of Damage: Posterolateral Part of Medulla and Includes the
Following Structures
Clinical Features Corresponding to the Structure Damaged
Lateral spinothalamic tract
Loss of pain and temperature below neck on the opposite side of the
body
Inferior cerebellar peduncle, spinocerebellar tracts and part of
cerebellum supplied by posterior inferior cerebellar artery
Loss of equilibrium (ataxia) of gait and limbs on the same side of
lesion
Damage to spinal nucleus and tract of trigeminal nerve
Loss of pain and temperature sensations of the face on the same side
of the body
Vestibular nucleus
Vertigo, nausea, vomiting and nystagmus
Nucleus ambiguus
Dysphagia (difficulty in swallowing due to paralysis of pharyngeal
and palatal muscles on the same side)
Difficulty in speaking (due to paralysis of laryngeal muscles of the
same side)
Descending sympathetic fibres from hypothalamus to preganglion-
ic sympathetic neurons of the thoracic spinal cord. This tract
descends in the reticular formation of medulla
Horner’s syndrome on the same side of lesion. Characterised by
ptosis (drooping of the upper eye lid), enophthalmos (retracted
eye ball in the orbit), myosis (constricted pupil), anhydrosis (loss
of sweating on that side of the face) and flushing of face.
SUMMARY
The brainstem consists of the medulla, pons and midbrain
•
(
Fig. 10.1
). It is continuous above with the forebrain and
below with the spinal cord. The brainstem is connected
posteriorly to cerebellum with the help of superior, mid-
dle and inferior cerebellar peduncles (
Fig. 10.3
).
The medulla, pons and cerebellum are collectively known
•
as hindbrain.
The brainstem gives attachment to cranial nerves III to
•
XII (
Figs 10.1
and
10.3
).
The medulla is conical in shape, and related anteriorly to
•
the basilar part of the occipital bone is posterior cranial
fossa.
As indicated in
•
Figures 10.2
and
10.3
, the medulla is di-
vided into an upper open part and a lower closed part.
The ventral surface shows the presence of anterior me-
•
dian fissure, pyramid, anterolateral sulcus, olive and pos-
terolateral sulcus (
Fig. 10.1
).
The anterolateral and posterolateral sulci give attach-
•
ments to cranial nerves IX to XII.
The dorsal surface of the lower (closed) part of medulla
•
shows the presence of posteromedian sulcus, gracile tuber-
cle, cuneate tubercle and posterolateral sulcus (
Fig. 10.7
).
Transverse section at the level of pyramidal decussation
•
resembles the spinal cord. The most striking feature is py-
ramidal decussation and appearance of the lateral corti-
cospinal tract (
Fig. 10.9a
).
The dorsal grey horn of the spinal cord is replaced by the
•
nucleus of the spinal tract of the trigeminal nerve.
The caudal ends of gracile and cuneatus nuclei start ap-
•
pearing in the posterior grey column (
Fig. 10.9a
).
Transverse section at the level of sensory decussation
•
shows three nuclei in the central grey matter—hypoglos-
sal, dorsal vagal and nucleus of solitary tract. Nuclei gra-
cilis and cuneatus are now a separate mass of grey matter
on the posterior aspect of the section. The nucleus of the
spinal tract of trigeminal is situated in the lateral part of
the sections. Nucleus ambiguus is situated in the area of
reticular formation.
The fibres arising from gracile and cuneate nuclei are
•
known as internal arcuate fibres. The internal arcuate fi-
bres of two sides decussate in the median plane, which is
known as sensory decussation (
Fig. 10.10
). After decus-
sation, these fibres form the medial lemniscus (
Figs 10.9
and
10.11
).
The medial longitudinal bundle is located anterior to the
•
hypoglossal nucleus. In the anterior area of the section
are pyramids on either side of the anterior median fissure
containing corticospinal fibres. The anterior and posterior
Table 10.2
Medial Medullary Syndrome (Due to Occlusion of the Anterior Spinal Artery)
Site of Damage: Ventromedial Part of Medulla
and Includes the Following Structures
Clinical Features
Pyramid (corticospinal tract)
This results in hemiplegia (paralysis) of the opposite side of body. This is an upper mo-
tor neuron type of paralysis.
Medial lemniscus (fibres carrying proprioceptive
impulses from the opposite side of the body)
Loss of sense of position, of movement and of discriminatory touch on the opposite
side of the body
Fibres and/or nucleus of the hypoglossal nerve
Tongue muscles on the same half are paralysed. Deviation of tongue to the paralysed
side when protruded out
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