2. The meninges

Question 1

describe the meningeal layers

Answer 1

1. PIA: vascular layer tightly adherent to brain and spinal cord - protects brain from chemical insults
2. SUBARACHNOID SPACE: contains CSF to cushion brain
3. ARACHNOID: CT layer
4. SUBDURAL SPACE: between dura and arachnoid
5. DURA: thick and inextensible CT
   - MENINGEAL DURA: adjacent to arachnoid
   - PERIOSTEAL DURA: endosteum of skull bones

Question 2

what structures are formed between the periosteal and meningeal dural layers

Answer 2

dural venous sinuses, e.g. superior and inferior saggital sinuses

Question 3

name 2 important folds formed by meningeal dura and describe their attachments

Answer 3

• falx cerebri (sagittal plane): ethmoid bone anteriorly, skull vault superior and posterior and free inferior edge
• tentorium cerebelli (transverse plane): extends from ridge of petrous temporal bone and clinoid processes to occipital protuberance

Question 4

name and give 2 differences between these 2 types of bleed

Answer 4

1. EXTRADURAL HAEMATOMA
   - arterial blood from BVs within dura, e.g. middle meningeal artery
   - biconcave shape as is limited by suture lines
2. SUBDURAL HAEMATOMA
   - venous blood from bridging veins spanning subdural space (esp. after stretching in elderly)
   - ‘banana’ shape as isn’t limited by suture lines

Question 5

what is the weakest part of the skull and why is a fracture here particularly dangerous

Answer 5

• pterior: cross-section between frontal, parietal, temporal and sphenoid bones - thinnest area
• anterior division of middle meningeal a. runs beneath - risk of extradural haemorrhage

Question 6

describe the trilaminar arrangement of bones of the calvaria

Answer 6

• periosteum
• outer table (compact)
• diploeic cavity (spongy trabeculae)
• inner table (compact)
• endosteum/periosteal dura

Question 7

which structures are present at the intersection of skull bones - name the most important ones

Answer 7

• sutures: fibrous joints that ossify from inside out once growth has finished
• periosteum continuous throughout suture line - limits extradural haemorrhages and subperiosteal cephalohaematomas
• sagittal, coronal, lambdoid

Question 8

what are fontanelles, their function and where are these located

Answer 8

• fontanelles = large areas of unossified membranous gaps beween flat bones of calvaria
• allow for alteration of skull size and shape during birth and permit growth of infant brain
• anterior fontanelle at coronal suture level and posterior fontanelle at lambdoid suture level

Question 9

when do the fontanelles fuse, via which process does this occur and what are the vestigial areas named

Answer 9

fusion via intramembranous ossification

• anterior fontanelle: 18 mths-2 yrs (becomes bregma area)
• posterior fontanelle: 2-3 mths (becomes lambda area)

Question 10

what is a sunken or a bulging fontanelle a sign of

Answer 10

• sunken = dehydration
• bulging = raised intracranial pressure

Question 11

which symptoms/signs suggest a basilar skull fracture

Answer 11

1. battle’s sign (bruising over mastoid process)
2. raccon eyes (bruising around both eyes)
3. haemotympanum (blood behind eardrum)
4. CSH rhinorrhoea or otorrhoea