The meningeal veins are very thinwalled veins which lie between the meningeal arteries and the bone. They end either in the venous sinuses or in veins outside the skull by passing through forami
na with the corresponding arteries.
See Clinical Applications 8.1, 8.2, and 8.3 for the practical implications of the anatomy discussed in this chapter.
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The cranial cavity
CLINICAL APPLICATION 8.1 Cavernous sinus thrombosis A 52-year-old lady with dental caries and a persistent root
abscess presented to the emergency department with se- vere unilateral throbbing headache, double vision, loss of sensation over the upper face, periorbital swelling, and pain on the right side.
Study question 1: what is the likely diagnosis? (Answer:
cavernous sinus thrombosis (CST). Other differential diagno- sis includes migraine headache and orbital cellulitis.)
Study question 2: what is cavernous sinus thrombosis?
(Answer: CST is thrombosis—clot formation—in the cavern- ous sinus, resulting from spread of infection from the nose, paranasal air sinuses, tonsils, or tooth. It has high morbidity and can have residual visual impairment and cranial nerve deficits.)
Study question 3: what are the veins connected with the cavernous sinus? (Answer: the cavernous sinus receives the superior and inferior ophthalmic veins, the central retinal vein of the retina, the middle meningeal veins, and the pterygoid venous plexus via emissary veins. It also receives
venous blood from the brain through the superficial middle cerebral veins. It drains into the sigmoid sinus via the supe- rior petrosal sinus, and into the internal jugular vein via the inferior petrosal sinus.)
Study question 4: explain the anatomical basis for the symptoms experienced by this patient. (Answer: the head- ache is a result of meningeal irritation. Swelling and peri- orbital oedema occur due to venous congestion of the ophthalmic veins. Visual impairment may occur due to papilloedema and retinal haemorrhage secondary to reti- nal congestion. Other symptoms of CST occur because of the close relationship between the cavernous sinus and the third, fourth, fifth—ophthalmic and maxillary divisions—
and sixth cranial nerves in the lateral wall of the cavern- ous sinus. Pain and loss of sensation over the upper face are the result of stretching/pressure of the ophthalmic and maxillary divisions of the trigeminal nerve. Double vision (diplopia) usually persists due to involvement of the sixth cranial nerve.)
CLINICAL APPLICATION 8.2 Pituitary adenoma A 28-year-old unmarried woman presented with a history
of amenorrhoea (lack of menstruation) and spontaneous secretion of milk from her breasts for the past year. She also reported recent onset of headache and visual disturbances.
Testing for visual fields revealed bitemporal hemianopia—
loss of temporal field of vision. Computerized tomography (CT) scans showed a large pituitary adenoma [Fig. 8.18].
Study question 1: why does the patient experience visual disturbance? (Answer: a large pituitary adenoma can com- press the optic chiasma above and disrupt the nasal fibres from the retina. This causes bitemporal hemianopia.)
Study question 2: what cell type could this tumour be composed of? (Answer: the history suggests a prolactin- secreting tumour called prolactinoma. This causes secretion of breast milk, even in non-lactating women (galactorrhoea).
High content of prolactin in the circulating blood can cause suppression of the menstrual cycle (amenorrhoea) and ano- vular cycles leading to infertility.)
Study question 3: what are the other tumours of the pituitary gland? (Answer: other common hormone-secreting tumours are somatotrophic adenomas—secrete growth hormone;
corticotrophic adenomas—secrete adrenocorticotrophin; and
gonadotrophic adenomas—secrete follicle-stimulating hor- mone (FSH) or luteinizing hormone (LH).)
Study question 4: how are these tumours treated?
(Answer: most tumours resolve with medicines. Others can be treated with surgery. The endonasal trans-sphenoidal ap- proach to the pituitary is commonly used.)
Fig. 8.18 T1-weighted sagittal magnetic resonance imaging (MRI) of a pituitary macroadenoma, sagittal view. Arrows = boundary of macroadenoma; S = sphenoid air sinus.
S
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Dura mater of the base of the skull
CLINICAL APPLICATION 8.3 Intracranial haemorrhage—epidural vs subdural haematomas A 23-year-old man sustained a head injury in a road traf-
fic accident. He was conscious for a short while and then lapsed into a coma. He was suspected of having an intracra- nial haemorrhage. Intracranial haemorrhages can be classi- fied according to location as: (1) extradural; (2) subdural; (3) subarachnoid; and (4) intracerebral.
Study question 1: use your knowledge of anatomy and Figs. 8.1 and 8.3 to determine which vessels would be the source of bleeding in: (1) extradural; (2) subdural; and (3) subarachnoid haemorrhage. (Answer: (1) extradural haem- orrhage = meningeal vessels; (2) subdural haemorrhage = bridging veins as they run from the subarachnoid space to the superior sagittal sinus; and (3) subarachnoid haemor- rhage = cerebral vessels.)
With time, blood from ruptured vessels collects within the confines of the space and forms a haematoma. Epidural haematomas are formed by high-pressure arterial blood rapidly filling the space between the dura mater and bone.
On CT, they are shaped like a biconvex lens and are confined to the area bound by sutures (as the dura is firmly adherent to the bone at the sutures and does not separate easily). If the dura mater is torn, bleeding from extradural vessels can spread into the subdural space.
Subdural haematomas result in slowly developing brain compression and unconsciousness, and are formed by ve- nous blood. They lie between the dura and arachnoid mater.
On CTs, they are crescent-shaped and follow the contours of the brain.
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chapter 9
Deep dissection of the neck
across the midline by a narrow isthmus [Fig. 9.2].
It extends from the oblique line on the thyroid car- tilage down to the fifth or sixth tracheal ring. It is enclosed in a sheath of pre-tracheal fascia which is attached above to the oblique line of the thyroid cartilage and to the arch of the cricoid cartilage.
This attachment to the thyroid cartilage means that the thyroid moves with the larynx in swal- lowing and speaking—a feature which helps to differentiate swellings of the thyroid gland from those of adjacent structures. Deep to the covering formed by the pre-tracheal fascia is the fibrous capsule of the gland. Between the pre-tracheal fascia and the fibrous capsule are the arteries and veins. The gland varies greatly in size and is relatively larger in women and children than in men.