92 / 264
with one study.
7
If non-invasive imaging is negative
in the setting of arterial tinnitus (particularly if it
is objective) then conventional angiography should
be considered to exclude a small dAVF.
Fig. 1
sum-
marizes the suggested imaging algorithm.
Causes of PT and their radiological
manifestations
Table 2
summarizes the causes of PT.
Visible intratympanic or retrotympanic mass
The three entities that may be diagnosed in this
setting are arterial anomalies, exposed jugular
bulb, or an intratympanic tumour (most frequently
paraganglioma). An aberrant ICA is an uncommon
anomaly due to failure of formation of the prox-
imal ICA in foetal life. This is replaced by the
inferior tympanic artery and enters the skull
lateral to the expected position of the vertical
portion of the carotid canal (which is absent)
(
Fig. 2
). The artery then passes through an en-
larged inferior tympanic canaliculus along the me-
dial aspect of the middle ear where it forms the
petrous ICA. An aberrant course of the ICA mani-
fests as a vascular retrotympanic mass and may
provoke a biopsy with disastrous consequences.
5,6
An aberrant ICA may also be associated with the
rare finding of a persistent stapedial artery (PSA),
which arises from the petrous ICA, enters the
hypotympanum, courses through the obturator
foramen (between the stapes crura), and enlarges
the tympanic segment of the facial nerve.
10
As the
PSA replaces the normal middle meningeal artery,
the foramen spinosum is absent or hypoplastic.
10
A
normally sited ICA, which is dehiscent into the
mesotympanum, may also cause PT and present
a surgical hazard.
Jugular bulb anomalies may be associated with
PT and if the jugular plate is dehiscent, this
manifests as a bluish mass at otoscopy.
Paraganglioma or glomus tumour is the most
common neoplastic cause of PT.
6
This is a benign,
but locally aggressive, tumour which arises from
glomus bodies (chemoreceptor cells) at predict-
able locations along nerves. Glomus jugulare, tym-
panicum and jugulotympanicum (
Fig. 3
) are
associated with PT. Glomus jugulare arises along
the adventitia of the jugular bulb. The cochlear
promontory is the most common site of glomus
tympanicum.
11
On CT, glomus tumours cause per-
meative erosion of the skull base and CT is the
ideal technique for defining the extent of tumour.
Widening of the inferior tympanic canniliculus in
glomus jugulare, due to hypertrophy of the artery,
is a useful early sign of tumour.
12
The vascular
Persistent pulsatile tinnitus
Exclude non-structural causes
Intra/retrotympanic mass
Normal otoscopy
CT
Arterial
Venous
Non-pulse synchronous
MR&MRA or CTA/V MR&MRV or CTA/V
CT/MRI
If negative consider catheter angiography (especially if objective tinnitus)
Figure 1
Imaging algorithm for PT.
Imaging in pulsatile tinnitus
71