6. Head and Neck p314-326 (Skull Base and Sinuses)

Question 1

Petrous Apex - anatomic variants (3)

Answer 1

Asymmetric marrow,
Cephaloceles
Variant anatomy of the carotid artery

Question 2

Asymmetric marrow (3)

Answer 2

Typically petrous apex contains significant fat, closely following the scalp and orbital fat (T1 and T2 bright).
Asymmetry can mimic infiltrative process.
Could also overlook a T1 bright pathology (cholesterol granuloma) thinking it’s fat.
Key is to use STIR or fat sat.

Question 3

Cephalocele (4)

Answer 3

herniation of CNS content through a defect in the cranium.
In the petrous apex, they don’t contain brain tissue and represent cystic expansion and herniation of the posterolateral portion of Meckel’s cave into the superiomedial aspec of the petrous apex.
Usually unilateral and classically described as “Smoothly marginated lobulated cystic expansion of the petrous apex”

Question 4

Variant anatomy of the carotid artery (3)

Answer 4

2 main variants are persistent stapedal artery and aberrant internal carotid.
DONT biopsy them.
They can cause pulsatile tinnitus.

Question 5

Inflammatory lesions of the Petrous apex (4)

Answer 5

Cholesterol Granuloma
Cholesteatoma
Apical petrositis.
Grandenigo syndrome

Question 6

Cholesterol granuloma (7)

Answer 6

commonest primary petrous apex lesion.
Likely due to obstruction of the air cell, with repeated cycles of haemorrhage and inflammation, leading to expansion and bone remodelling.
Most common symptom is hearing loss.
CT: Margins sharply defined.
MRI: T1 and T2 bright, with T2 dark haemosiderin rim and faint peripheral enhancement.
No diffusion restriction.
Faster growing ones need surgery.

Question 7

Cholesteatoma (4)

Answer 7

Epidermoid (ectopic epithelial tissue).
They are congenital in the petrous apex.
Slow growing, with bony change similar to cholesterol granuloma.
MRI is T1 DARK, T2 bright, restricts diffusion.

Question 8

Apical petrositis (9)

Answer 8

Infection of petrous apex is a rare complication of infectious otomastoiditis.
Has complications if it progresses, including:
- osteomyelitis of skull base,
- ICA Vasospasm,
- subdural empyema,
- CVST,
- tempral lobe stroke and
- meningitis.
Can present as primary process in kids.
In adults, usually in setting of chronic otomastoiditis or recurrent mastoid surgery.

Question 9

Grandenigo syndrome (5)

Answer 9

Complication of apical petrositis, when Dorello’s canal (CN 6) is involved.
Causes lateral rectus palsy.
Classic triad of:
- Otomastoiditis
- Face pain (trigeminal neuralgia)
- Lateral rectus palsy

Question 10

Petrous apex tumours (2)

Answer 10

Endolymphatic sac tumour
Paraganglioma

Question 11

Endolymphatic sac tumour (5)

Answer 11

rare tumour of the endolymphatic sac and duct.
Most are sporadic, but also associated with VHL.
Usually grow into the CPA.
Internal amorphous calcifications on CT.
T2 bright with intense enhancement.
Very vascular, often with flow voids and tumour blush on angiography.

Question 12

Paraganglioma (5)

Answer 12

Paraganglioma of the jugular fossa (glomus jugulare or jugulotmypanic tumours) can invade the occupital bone and adjacent petrous apex.
Hereditary in 40%, with multiple tumours.
Most commonly presents with voice hoarseness, from vagal nerve compression.
Very vascular and enhance avidly with “salt and pepper” appearance on post contrast MRI with flow voids.
FDG avid.

Question 13

Large vestibuar aqueduct syndrome (6)

Answer 13

Vestibular aqueduct is a bony canal that connects the vestibule (inner ear) with the endolymohatic sac.
When it’s enlarged (>1.5cm), associated with sensorineural hearing loss.
This syndrome associated with absence of bony modiolus in more than 90%.
Result of failure of endolymohatic sac to resorb endolymph, leading to endolymphatic hydrops and dilatation.
Commonest cause of congenital sensorineural hearing loss.
Usually bilateral.
Associated with cochlear deformity

Question 14

Labyrinthitis (2)

Answer 14

Inflammation of the membranous labyrinth, most commonly due to viral infection.
Cochlea and semicircular canals enhance on T1 post contrast

Question 15

Labyrinthitis Ossificans (3)

Answer 15

Sequella of prior infection, usually meningitis.
Seen in kids 2-18 months.
CT: ossification of the membranous labyrinth.
Causes sensorineural hearing loss.

Question 16

Otosclerosis (5)

Answer 16

Bone becomes more lytic.
Usually the cause of conductive hearing loss in a female adult.
2 kinds:
Fenestral: Bony resorption anterior to the oval window, at the fussula ante fenestram. Of not addressed, the footplate will fuse to the oval window.
Retro-fenestral: more severe form which has progressed to have demineralisation around the cochlea. Usually has sensorineural component and is usually bilateral and symmetric

Question 17

Otitis media (3)

Answer 17

Common childhood disease, effusion and infection of the middle ear.
More common in children and Downs (more horizontal eustachian tube).
Chronic if fluid persisting for >6 weeks.

Question 18

Otitis media complications (5)

Answer 18

Coalescent mastoiditis - erosion of the mastoid space with or without intramastoid abscess.
Facial nerve palsy - Secodnary to inflammation of the tympanic segment
Dural sinus thrombosis - Adjacent inflammation may cause thrombophlebitis or thrombosis of the sinus. This itself leads to other complications (venous infarct, Otitic hydrocephalus due to poor CSF resorption)
Meningitis and labyrinthitis.

Question 19

Cholesteatoma (3)

Answer 19

Exfoliated skin debris growing in the wrong place, creating a ball of inflammation which damages the temporal bone and ossicles.
2 parts to the eardrum, pars flaccida (flaccid) and pars tensa (more rigid, inferior).
A “hole” with some inflammation or infection involving the pars flaccida can cause a cholesteatoma.

Question 20

Cholesteatoma order of destruction (3)

Answer 20

The scutum,
The ossicles (long process of incus)
The lateral segment of the semi-circular canal

Question 21

Pars flaccida vs Pars tensa cholesteatoma (6)

Answer 21

Pars flaccida
- Acquired is more common, typically involving pars flaccida. Can grow into Prissak’s space.
- Scutum is eroded early, considered specific sign of acquired cholesteatoma.
- Malleus is displaced medially.
- Long process of incus is most common segment of ossicular chain to be eroded.
- Fistula to semi-circular canal most commonly involves lateral segment
Pars tensa
- Inner ear structures are involved earleir and more often.
- Less common than flaccida type

Question 22

Labyrinthine fistula (3)

Answer 22

Complication of cholesteatoma, can also be congenital or iatrogenic.
Bony defect between the inner ear and tympanic cavity.
Lateral semicircular canal is most often involved.

Question 23

Relevant anatomy for cholesteatoma (6)

Answer 23

Coronal view of temporal bone:
Tympanic membrane usually too thin to see on CT.
Prussak’s space: space between incus and the lateral temporal bone. Most common location of pars flaccida Cholesteatoma. Incus is most commonly eroded bone.
Scutum is the first bone eroded by pars flaccida cholesteatoma.
Axial view:
Lateral portion of semicircular canal, first part the cholesteatoma will invade if it invades the semicircular canal

Question 24

Superior semicircular canal dehiscence (2)

Answer 24

Due to longstanding ICP.
Causes “noise induced vertigo” or “Tulio’s phenomenon”

Question 25

Necrotising Otitis Externa (2)

Answer 25

Aggressive infection, causing swollen external auditory canal tissues, with small abscesses and adjacent bony destruction.
Usually diabetic. Usually pseudomonas.

Question 26

Pagets of skull base (6)

Answer 26

Osteolysis - well defined large radiolucent region, favouring frontal and occipital bones.
Inner table is affected more than outer table.
“Osteolysis circumscripta”
Complications
- Deafness is most common.
- Cranial nerve paresis
- Basilar invagination
- Secondary (high grade) osteosarcoma

Question 27

Facial nerve trivia (5)

Answer 27

Cisternal, canalicular and labyrinthine segments should NOT enhance. The remainder will enhance, due to the perineural venous plexus.
Abnormal enhancement caused by Bell’s Palsy, Lyme’s, Ramsay hunt and cancer
Commonly damaged by transverse temporal bone fractures, more than longitudinal

Question 28

Chordoma and chondrosarcoma (3)

Answer 28

Can also affect skull base.
Chordoma is midline.
Chondrosarcoma is off midline

Question 29

Fibrous dysplasia (4)

Answer 29

Ground glass lesion, usually in younger person (30s) rather than pagets (80s).
Classically fibrous dysplasia of the skull spares the otic capsule.
McCune Albright syndrome: Multifocal fibrous dysplasia, cafe-au-lait spots and precocious puberty.

Question 30

Juvenile Nasal Angiofibroma (4)

Answer 30

Male teenager with nosebleeds. Obstruction is a common symptom.
Mass centered on the sphenopalatine foramen.
Expansion of the pterygopalatine fossa.
Very vascular, angiogram will blush.
Primary vascular supply from ascending pharyngeal artery and/or internal maxillary artery

Question 31

Antrochoanal polyp (6)

Answer 31

Seen in 30-40s, with nasal congestion and obstructive symptoms.
Arises within the maxillary sinuses and passes through and enlarges the sinus ostium (or accessory ostium).
“Widening of the maxillary ostium”.
No associated bony enlargement of the sinus.
Polyp extends into the nasopharynx.
Basically a large inflammatory polyp with a thin stalk arising from the maxillary sinus.