Despite advances in endoscopic techniques, there are still instances when the frontal sinus must be approached externally. Given its variable anatomy, the frontal sinus continues to present a challenge to the surgeon. Our rule of thumb capitalises on the consistent embryological development of the frontal sinus, aiding safe external access.

The presented stepwise approach includes trephination, fenestration, an osteoplastic flap and obliteration. The obliteration procedure has produced good results in managing those patients with disabling symptoms despite multiple endoscopic procedures.

The canal wall up bony obliteration technique lowers the incidence of recurrent cholesteatoma, but carries the potential risk of obliterating residual cholesteatoma. The objective of this study was to report long-term follow-up radiological findings after performing a canal wall up bony obliteration technique procedure, in order to detect residual and/or recurrent cholesteatoma.

Fifty-one patients presenting with a cholesteatoma or a troublesome cavity were operated upon using the canal wall up bony obliteration technique, and were evaluated by follow-up imaging a mean of 76.4 months post-operatively (range, 53.8–113.6 months).

All patients were evaluated with high resolution computed tomography and magnetic resonance imaging (including delayed contrast, T1-weighted imaging and non-echo-planar, diffusion-weighted imaging).

Imaging revealed the presence of one residual, one recurrent and one congenital petrosal apex cholesteatoma. On high resolution computed tomography, completely obliterated mastoid filled with bone was observed in 74.5 per cent (38/51) of patients, and an aerated middle-ear cavity in 64.7 per cent (33/51). High resolution computed tomography clearly detected any associated soft tissue present in the middle-ear cavity (18/51) and in the obliterated mastoids (13/51), but could not characterise this tissue. Non-echo-planar, diffusion-weighted magnetic resonance imaging clearly identified all three cholesteatomas, and differentiated them from other associated soft tissues. No cholesteatoma was found within the obliterated mastoids.

Long-term follow up indicated that the canal wall up bony obliteration technique is a safe method with which to treat primary and recurrent cholesteatoma and to reconstruct unstable cavities. Soft tissue was found quite often in the middle ear and obliterated mastoids. High resolution computed tomography identified its presence but could not further characterise it. However, non-echo-planar, diffusion-weighted magnetic resonance imaging succeeded in differentiating soft tissues, enabling detection of residual or recurrent cholesteatoma after a canal wall up bony obliteration technique procedure.