Page 363 - Clinical Anatomy

ECA6 7/18/06 6:54 PM Page 348

348 The central nervous system

dura mater (Fig. 215), with intercavernous sinuses communicating in front,
behind and below. The optic chiasma lies above, immediately in front of the
infundibulum.

Structure
The anterior lobe is extremely cellular and consists of chromophobe,
eosinophilic and basophilic cells. The pars intermedia contains large
colloid vesicles reminiscent of the thyroid. The posterior lobe is made up of
nerve fibres whose cell stations lie in the hypothalamus.

Development
The posterior lobe is a cerebral diverticulum. The anterior lobe and the
pars intermedia develop from Rathke’s pouch in the roof of the primitive
buccal cavity. Occasionally a tumour grows from remnants of the epithe-
lium of this pouch (craniopharyngioma). These tumours are often cystic
and calcified.

Clinical features

Tumours of the pituitary, as well as forming intracranial space-occupying
lesions, may have two special features; their endocrine disturbances and
their relationship to the optic chiasma.
Chromophobe adenoma is the commonest pituitary tumour. As it en-
larges it expands the pituitary fossa (sella turcica) and this may be demon-
strated radiologically. Compression of the optic chiasma produces the
very rapid typical bitemporal hemianopia (see ‘The optic nerve’, pages 365
and 366). The tumour itself is non-secretory and gradually destroys the
normally functioning gland. The patient develops hypopituitarism
with loss of sex characteristics, hypothyroidism and hypoadrenalism.
In childhood there is an arrest of growth. As the tumour extends there
may be involvement of the hypothalamus with diabetes insipidus and
obesity.
The eosinophil adenoma secretes the pituitary growth hormones. If it
occurs before puberty, which is unusual, it produces gigantism; after
puberty it results in acromegaly.
The basophil adenoma is small, produces no pressure effects and may be
associated with Cushing’s syndrome, although this more often results from
hyperplasia or tumour of the suprarenal cortex.
Pituitary tumours may be approached through a frontal bone flap or,
using the fibre-optic endoscope, through the nasal cavity and sphenoid
sinus.
The close relationship of the pituitary to the sphenoid sinus makes it
possible to insert fibre-optic instruments into the pituitary gland by a
transnasal, transsphenoidal approach. This is now the preferred approach
to surgery of pituitary tumours.