Osteology, Radiology, Meninges, Dural Folds and Venous Sinuses

Question 1

What’s the difference between neuro and viscerocranium?

Answer 1

Neurocranium surrounds the brain and viscerocranium the face.

Question 2

He skull is made of 22 bones with different features. What do the following mean: fossae, canal, foramina and fissures?

Answer 2

Fossae are shallow depressions/ hollows (skull has ant, middle and post). A canal is a bony tunnel. Foramina are round and fissures are narrow holes.

Question 3

8 bones make up the neurocranium to encase and protect the brain, with the calvaria (skull cap), cranial floor and cranial cavity. How do these bones develop?

Answer 3

Cal aria bones begin through intramembranous ossification and the floor by endochondrial ossification.

Question 4

There are 14 bones in the viscerocranium (which develop mostly from the pharyngeal arches), making up the facial skeleton and jaw, what do they surround?

Answer 4

The oral cavity, pharynx and upper respiratory tract.

Question 5

Why does the cranial floor need holes in it?

Answer 5

For cranial nerve communication with the face and neck and blood vessels need to pass in and out.

Question 6

Internally the neurocranium has 3 fossae on the cranial floor to seat different parts of the brain (and associated structures), what features might be seen in them?

Answer 6

Each has a set of foramina, some have fissures and canals for communication and the bone is grooved by the location of sural venous sinuses.

Question 7

Describe and explain the function of the trilaminar arrangement of the calvaria.

Answer 7

Compact bone makes the outer table, then spongy for diploeic cavity and then compact inner table. This arrangement confers strength without adding significant weight.

Question 8

The edge of neurocranium bones are serrated at sutures, so there is not slippage or movement. Name 3 important duties in the skull.

Answer 8

Sagittarius, coronal, lambdoid.

Question 9

When do eps growth of skull sutures stop?

Answer 9

Growth is stopped around puberty and the obliterated inside to outside.

Question 10

What is the importance of suture lines in the boundaries of Cephalohaematoma?

Answer 10

This bleed between the periosteum and skull cannot pass intracranially over over suture lines, as the periosteum covers the outer table and strongly adheres at suture lines, continuing through to the periosteum on the inner table.

Question 11

What are fontanelles and their purpose?

Answer 11

Large areas of unossified membranous gaps between flat bones of the calvaria in an infant, that allow for skull shape/size alteration during birth and permit growth of the infant brain.

Question 12

When do fontanelles fuse in a healthy individual and what is Early sutures of fontanelles and sutures known as?

Answer 12

Anterior fusion occurs at 1.5-2 years and posterior fusion 1-3 months.
Craniosyntosis.

Question 13

What can examination of the fontanelles tell you?

Answer 13

Inspection and gentle palpation of anterior fontanelles is used to access intracranial pressure and state of hydration (in context) - healthy is slightly convex.

Question 14

What type of imaging is used in a ‘bone window’ to see the suture lines and layers of the bone at an axial view?

Answer 14

CT scan

Question 15

Significant force/ trauma is needed for a skull, is the same force needed the whole way around it?

Answer 15

No, the skull has variable thickness and so resistance to breaking.

Question 16

What is the main concern with a skull fracture and how can this be viewed?

Answer 16

Intracranial injury (skull doesn’t have to be fractured for it) of the brain, blood vessels or cranial nerves, so do a CT scan.

Question 17

What are the 2 types of skull fracture and how do they differ structurally?

Answer 17

Linear fractures pass the full thickness through the skull, so are fairly straight and there’s no displacement.
Depressed fractures involve a segment displaced inwards.

Question 18

What is a fracture involving the cranial base called and what may be associated?

Answer 18

Basilar skull fractures may have associated cranial nerve injury, CSF leakage and other signs (Racoon eyes or Battle sign-behind ear, also look in ear).

Question 19

What is the Pterion and what type of haemorrhage can injury to this site cause?

Answer 19

The Pterion is where many bones meet at the side of the skull and where it is at its thinnest, so easiest to fracture. The (anterior branch of the) middle meningeal artery sits underneath it and bleeding of this can cause an extradural intracranial haemorrhage.

Question 20

What will have if there is trauma to the supraorbital ridge and supracillary arch?

Answer 20

They are very tough, so likely that the skin will split.

Question 21

Which bones are commonly fractured in the face?

Answer 21

Fracture of nasal bone, zygomatic bones and arch are common, as well as the mandible.

Question 22

What are the meninges and their 3 layers?

Answer 22

Membranous layers that surround and protect the brain.
Pia - microscopically thin and adherent to brain surface, Arachnoid - soft, translucent membrane, Dura - tough, fibrous membrane.

Question 23

Where in relation to the meninges, do blood vessels and CSF run?

Answer 23

Blood vessels run in the subdural space and CSF with cerebral blood vessels Andre in the subarachnoid space.

Question 24

The arachnoid layer does not dip into the ______, but does between the ______________. The dura is strongly adhered to the _______ ________.

Answer 24

Sulci
Hemispheres
Inner table

Question 25

Give an example of a blood vessel that runs outside of the dura.

Answer 25

The meningeal arteries - supply dura and bones of the calvaria.

Question 26

Describe the relationship between the 2 layers of the dura - how do folds and sinuses fit in?

Answer 26

The periosteal and meningeal layers mostly stay adhered, but separation forms dural folds and dura venous sinuses - spaces become venous channels. A fold is from 2 fused meningeal layers.

Question 27

What do channels of venous blood from the brain ultimately drain into?

Answer 27

Internal jugular vein. (Cerebral veins->DVS->IJV)

Question 28

Name and describe the positions of 2 important dura folds.

Answer 28

The Falx cerbri has a triangular venous sinus and attaches to the crista galli in the ethmoid bone. It hooks up the Tentorium cerebelli sitting above the cerebellum, which has the tentorial notch for passage of the brainstem.

Question 29

Why are dural folds usually helpful and when can they become a problem?

Answer 29

Dural folds stabilise the brain as rigid dividers, but when there’s raised intracranial pressure (e.g. From tumour or haemorrhage) here may be compression and displacement of the brain against them / through the foramen magnum - herniation leads to neurological signs.

Question 30

Where do major dural venous sinuses tend to sit?

Answer 30

They tend to lie at the borders of Falx cerebri and Tentorium cerebelli, as well as the cranial floor.

Question 31

Describe the relationships and positions of the following dural venous sinuses: transverse, straight, petrosal, sagittal, cavernous, sigmoid.

Answer 31

Inferior and superior sagittal sinuses from FC are connected posteriorly by the straight sinus. The transverse sinuses comes round from the back of the skull to drain into the horizontal sigmoid sinus, which leads to a hole in the base of the skull and becomes the IJV. Also draining in are the cavernous sinuses from either side of the sella turcica, getting there by the superior and inferior patrosal sinuses.

Question 32

How do the cerebral veins connect with the dural venous sinuses?

Answer 32

Bridging veins transverse the subdural space and cerebral veins within the subarachnoid space drain into the dural venous sinuses. (Emissary veins bring scalp veins to sinuses)

Question 33

Blood vessels that run along or traverse meningeal layers may be injured and bleed, where might blood accumulate?

Answer 33

Extra dural, subdural or subarachnoid spaces. Blood from the brain itself - intracerebral haemorrhage.

Question 34

Pressure may damage tissue, brainstem and other structures (e.g. CNs). Give 2 features of an extradural haemorrhage.

Answer 34

Arterial blood, limited by suture lines, as dura strongly adhered.

Question 35

Describe a subdural haemorrhage.

Answer 35

Venous blood only stopped by Falx cerebri from travelling to contralateral hemisphere. Bridging veins are under more pressure with brain shrinkage.

Question 36

What might cause a subarachnoid haemorrhage?

Answer 36

An arterial bleed, secondary to trauma or spontaneous rupture (e.g. Aneurysm), usually of a branch of the Circle of Willis - blood mixes with CSF, sudden and often fatal.

Question 37

How are subarachnoid haemorrhages identified?

Answer 37

100% can be seen on a CT scan within 6 hours, 93% within 24 hours. A lumbar puncture is done if this is inconclusive to identify the presence of blood (Hb degradation products) - not if raised intracranial pressure.

Question 38

What is a haematoma?

Answer 38

A solid swelling of clotted blood in the tissues.