HSC Section 8_April 2017

studies were poorly sensitive and MRI/A de-

tected only 68% of cases. Although contempo-

rary imaging is likely to be more diagnostically

accurate overall, catheter angiography may still

be needed for the diagnosis of AVFs.

Intrameatal vascular loops

Based on radiological and surgical data some

investigators hypothesize that there is a relation-

ship between vascular loops extending deep into

the internal auditory meati and PT (

Fig. 10

). There

are reports relating neurovascular contact with the

vestibulocochlear nerve to non-PT and microvascu-

lar decompression has abolished tinnitus in some

cases.

23,24

Other studies found no significant rela-

tionship between intrameatal vascular loops and

tinnitus and a similar incidence of vestibuloco-

chlear neurovascular contact in the asymptomatic

population.

25,26

More recently, there have been

data specifically related to patients with PT.

Nowe´ et al.

found a significantly higher number

of vascular loops in the IAC (as opposed to within

the cerebellopontine angle) on MRI in patients

with PT compared with those with continuous tin-

nitus. It is proposed that turbulent flow within

the arterial loop creates sound waves that are con-

ducted within the cerebrospinal fluid and then

through the perineural spaces, via the fundus of

the IAC to the cochlea (by bone conduction).

Bone dysplasia

Otospongiosis (commonly called otosclerosis) is the

replacement of the normally dense middle layer of

the bony labyrinth with areas of ‘‘spongy’’ haver-

sian bone. Fenestral otospongiosis, which affects

the lateral bony labyrinth, is the most common

type and most frequently manifests as spongiosis

in the area anterior to the oval window (fissula

antefenestrum) with or without involvement of the

stapes footplate (

Fig. 11

). The condition is the

most common cause of mixed hearing loss in adults

and is bilateral in 85% of cases.

There is a 65

85%

reported prevalence of tinnitus (usually continu-

ous but occasionally pulsatile), which improves in

85% of patients following stapes surgery.

28,29

Paget’s disease may cause demineralization

of the temporal bone resulting in hearing loss,

vestibular dysfunction, or tinnitus.

Continuous

Figure 10

Three-dimensional, T2-weighted, turbo

spin-echo, driven equilibrium (TSE DRIVE) transverse im-

age in a patient with continuous left-sided tinnitus. The

presence of bilateral deep intrameatal vascular loops

(seen to arise from the anterior inferior cerebellar ar-

teries) are most likely incidental.

Figure 11

Transverse CT section demonstrates conflu-

ent pericochlear radiolucency in a patient with cochlear

otospongiosis.

Figure 12

Transverse CT section in a patient with ex-

tensive lytic Paget’s disease of the skull base and vault

with biochemical and isotope bone scintigraphy features

of the disease. Note the lucency on the right petrous

temporal bone (arrowhead), basisphenoid, and left pe-

trous apex. Bone thickening and heterogeneity is more

typical in the later phases.

Imaging in pulsatile tinnitus