HSC Section 8_April 2017

Imaging in pulsatile tinnitus

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.

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

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

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)

Imaging algorithm for PT.

Figure 1

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