6. Head and Neck p314-326 (Skull Base and Sinuses) Flashcards
Petrous Apex - anatomic variants (3)
Asymmetric marrow,
Cephaloceles
Variant anatomy of the carotid artery
Asymmetric marrow (3)
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.
Cephalocele (4)
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”
Variant anatomy of the carotid artery (3)
2 main variants are persistent stapedal artery and aberrant internal carotid.
DONT biopsy them.
They can cause pulsatile tinnitus.
Inflammatory lesions of the Petrous apex (4)
Cholesterol Granuloma
Cholesteatoma
Apical petrositis.
Grandenigo syndrome
Cholesterol granuloma (7)
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.
Cholesteatoma (4)
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.
Apical petrositis (9)
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.
Grandenigo syndrome (5)
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
Petrous apex tumours (2)
Endolymphatic sac tumour
Paraganglioma
Endolymphatic sac tumour (5)
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.
Paraganglioma (5)
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.
Large vestibuar aqueduct syndrome (6)
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
Labyrinthitis (2)
Inflammation of the membranous labyrinth, most commonly due to viral infection.
Cochlea and semicircular canals enhance on T1 post contrast
Labyrinthitis Ossificans (3)
Sequella of prior infection, usually meningitis.
Seen in kids 2-18 months.
CT: ossification of the membranous labyrinth.
Causes sensorineural hearing loss.
Otosclerosis (5)
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. If 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
Otitis media (3)
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.
Otitis media complications (5)
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.
Cholesteatoma (3)
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.
Cholesteatoma order of destruction (3)
The scutum,
The ossicles (long process of incus)
The lateral segment of the semi-circular canal
Pars flaccida vs Pars tensa cholesteatoma (6)
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
Labyrinthine fistula (3)
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.
Relevant anatomy for cholesteatoma (6)
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
Superior semicircular canal dehiscence (2)
Due to longstanding ICP.
Causes “noise induced vertigo” or “Tulio’s phenomenon”
