Why use a CISS/FIESTA sequence for the IACs?

It is a heavily T2-weighted steady-state sequence in which fluid is bright and nerves are black. That creates a 'myelogram' effect inside the fluid-filled internal auditory canal, so the tiny VII and VIII nerves stand out and a small tumour shows as a filling defect.

Why does head symmetry matter for IAC imaging?

The two sides are compared directly. A tilted head makes one canal look different from the other, which can mask or mimic a lesion — so the head is repositioned straight rather than corrected by angling slices.

How does an acoustic neuroma appear?

As a dark filling defect within the bright CSF of the canal, classically 'ice-cream-cone' shaped where it extends into the cerebellopontine angle, and it enhances vividly on post-contrast T1.

Resources/Protocols

Internal auditory canals (IAC)

The hearing-loss protocol. You are imaging cranial nerves VII and VIII inside a fluid-filled canal — so a heavily T2-weighted steady-state sequence makes the nerves black against bright CSF, a 'myelogram' of the canal.

Protocols/Brain

When this study is used

Sensorineural hearing loss or tinnitus.
Suspected acoustic neuroma (vestibular schwannoma).
Facial-nerve symptoms or vertigo.

Patient & coil positioning

Head-first supine in a high-channel head coil; head straight so the two canals are symmetric for comparison.
Centre on the glabella; immobilise firmly for the thin high-resolution slices.
Warn the patient this is a still, quiet-demanding exam.

Localizer

Three-plane localizer; the axial must be straight through both IACs — reposition the patient if tilted rather than relying on angling alone.

Sequence planning

Each sequence below lists how the slice group is positioned — the reference line it follows, its coverage, and why it earns its place in the protocol. Plan against the localizer, not by eye.

Axial high-res T2 (CISS / FIESTA)

Axial

Planning — Thin sub-millimetre steady-state slices angled to the nerve bundle as it exits the brainstem; both canals.

Why — The VII/VIII complex as black filling-defects inside bright CSF — the core sequence.

Axial T1 + contrast fat-sat

Axial

Planning — Matched coverage.

Why — Schwannomas enhance vividly against suppressed fat.

Coronal T1 + contrast

Coronal

Planning — Through the canals.

Why — Second plane confirming an enhancing lesion and its extent.

Representative parameters

Ranges, not commandments — field strength, coil and vendor move the numbers. What must not move is understanding why each sits where it does.

Sequence	Slice	Notes
CISS / FIESTA	≤1 mm	Steady-state; nerves black in bright CSF
T1 +C fat-sat	≤3 mm	Schwannoma enhancement
Coronal T1 +C	≤3 mm	Second plane

Artifacts & how to fix them

Artifact	Typical cause	Mitigation
Pulsation over brainstem	Basilar-artery / CSF pulsation	Phase A–P; flow compensation; presaturation over the neck
Asymmetric canals	Tilted head	Reposition straight before scanning
Susceptibility (petrous)	Air in the mastoid	Steady-state tolerates it; keep TE short on T1

What am I looking at?

You are not reporting the study, but recognising pathology helps you keep it in the field of view and know when to add a sequence or contrast. How the common findings read on the console:

Finding	Sequence to check	How it reads
Acoustic neuroma	Axial CISS / T1+C	Dark 'ice-cream-cone' filling defect in the bright canal; enhances on T1
Nerve asymmetry	Axial CISS	One nerve bundle thinner or displaced versus the other side

Review checklist

Axial straight through both IACs, symmetric.
Sub-millimetre steady-state acquired for the nerve complex.
Post-contrast in two planes if a lesion is suspected.
Pulsation artefact steered away from the brainstem.

Mistakes that cost repeats

A tilted head making the canals asymmetric and hard to compare.
Slices too thick to resolve the individual nerves.
Pulsation ghosts smearing the brainstem and canals.
Skipping contrast when a small schwannoma is possible.

Common questions

Why use a CISS/FIESTA sequence for the IACs?: It is a heavily T2-weighted steady-state sequence in which fluid is bright and nerves are black. That creates a 'myelogram' effect inside the fluid-filled internal auditory canal, so the tiny VII and VIII nerves stand out and a small tumour shows as a filling defect.
Why does head symmetry matter for IAC imaging?: The two sides are compared directly. A tilted head makes one canal look different from the other, which can mask or mimic a lesion — so the head is repositioned straight rather than corrected by angling slices.
How does an acoustic neuroma appear?: As a dark filling defect within the bright CSF of the canal, classically 'ice-cream-cone' shaped where it extends into the cerebellopontine angle, and it enhances vividly on post-contrast T1.

Try it in ScanFlo: Acquire a thin CISS through the IACs and look for the black nerves against bright CSF, comparing left with right. That symmetry check is how a small filling defect becomes obvious.

← All brain studies