CT Temporal Bones — High Resolution
From the arcuate eminence above to below the mastoid tip, covering both temporal bones for comparison.
Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.
When to use it
- Suspected cholesteatoma and pre-operative mapping of its extent, ossicular erosion and tegmen or facial canal dehiscence.
- Conductive hearing loss with an intact drum, for ossicular fixation, otosclerosis or congenital anomaly.
- Temporal bone trauma, including suspected fracture involving the otic capsule or facial nerve canal.
- Cochlear implant planning and post-operative electrode position.
- Complicated mastoiditis, particularly where coalescence or intracranial extension is suspected.
Technique
- Collimation wider than about 1 mm does not resolve the ossicular chain; sub-millimetre detector configuration is the defining feature of the protocol.
- Both sides are scanned and reviewed side by side even for a unilateral question.
- A very wide window (of the order of a 4000 HU width) is the standard review setting.
- Contrast belongs to a separate soft-tissue or vascular protocol; it is not added to this one.
Where it goes wrong
- Reconstructing at standard head slice thickness discards the entire point of the acquisition.
- A soft-tissue kernel blurs the stapes and the scutum, which is where cholesteatoma is called.
- Motion in a small child is the usual failure mode; feed-and-wrap or an age-appropriate immobilisation plan should be arranged before the appointment rather than after a failed attempt.
- CT shows bone, not tissue type: it cannot separate cholesteatoma from granulation or effusion, which is the routine reason for a subsequent non-echo-planar diffusion MRI.
Clinical questions that reach this study
Contrast
Acquisition
- Reconstruction
- Sub-millimetre acquisition, commonly reconstructed at around 0.6 mm section thickness in a sharp bone algorithm, with axial and coronal (and often Poschl and Stenvers oblique) reformats reviewed on a wide window.
- Preparation
- No preparation. Absolute stillness matters more than on any other head CT because the structures of interest are sub-millimetre.
Phases
Each phase is authored once and shared across every protocol that uses it, so the physiology below is the same wherever you meet it.
- Non-contrast (unenhanced)No injection. Acquired before any contrast is given.
Shows intrinsic tissue attenuation, and nothing else. The transferable principle is that contrast is anti-signal for anything that is already dense: calcification, acute haemorrhage, urinary and biliary calculi, iodine-containing or haemorrhagic fluid, and intrinsic fat all lose conspicuity, or become uninterpretable, once surrounding tissue enhances. It is also the only baseline against which enhancement can be measured, so any protocol that quantifies enhancement or washout (a lesion "enhances by X HU", adrenal absolute washout, renal mass characterisation) is arithmetically impossible without it. Conversely, an unenhanced series adds dose and no information whenever the question is purely about vascularity or perfusion.
Safety checks this protocol carries
Derived from the contrast agent and phases above, not authored here — which is why they cannot drift apart from what the protocol actually does.
- Child-sized technique and contrast dose· radiographer at scan
- Sedation or anaesthesia for a child· nurse pre scan