Computed tomography imaging of the paranasal sinuses: direct versus reformatted coronal images

Reduction of Radiation Dosage in Visualization of Paranasal Sinuses in Daily Routine

Background. Preoperative imaging of the nose and paranasal sinus is standard in otorhinolaryngology. Previous studies on phantoms demonstrated the potential for dose reduction of cone beam computed tomography (CBCT) by varying the application parameters. Methodology. Based on previous studies, the standard protocol of paranasal sinus imaging by CBCT was altered. One hundred and fifty examinations using the old protocol (01/2010–01/2011, high dosage) and 150 examinations using the new protocol (09/2012–09/2013, low dosage) were evaluated and compared for the visibility of 17 anatomical structures, the Lund-Mackay Score, and technical parameters. Results. Alteration of the protocol resulted in a significant reduction in dosage (6.64 mGy versus 2.88 mGy). Both groups showed the same amount of pathology (Lund-Mackay Score: 4.95 ± 3.79 versus 5.26 ± 5.77; p = 0.558). There was a significant better visibility of the anatomical structures (all visible = 1, nothing visible = 4) (results: 1.25 versus 1.17; p = 0.001) in the low-dosage group. Conclusion. Despite a significant reduction in the applied dosage, reliable visualization of the bony anatomy of the anterior skull base is possible by CBCT. This demonstrates the need for the discussion of the required clinical imaging quality.

Don't sue the surgeon: remineralisation of the skull base or a defect that never existed?

INTRODUCTION

Intracranial complications are recognised as rare, but serious, sequelae of endoscopic sinus surgery.

CASE REPORT

A 56-year-old woman was referred after developing meningitis following elective functional endoscopic sinus surgery. Computed tomography demonstrated a significant defect of the skull base in the right posterior ethmoid, clearly visible on both coronal and sagittal sections. Operative exploration demonstrated the skull base to be intact in the posterior ethmoid area identified on the scan, and the overlying mucosa appeared undisturbed. Scans were reviewed in the light of operative findings; coronal and sagittal images were found to be reconstructions. Directly acquired coronal computed tomography, undertaken three weeks after surgery, demonstrated a complete bony plate in the right posterior ethmoid at the site previously identified as dehiscent.

DISCUSSION AND CONCLUSION

We speculate that the posterior ethmoid defect was actually an artefact of reconstruction. We cannot exclude the alternative possibility of remineralisation, but given the time frame this seems unlikely. This case highlights the need for caution when interpreting reconstructed images of the thin bony plates of the skull base and lamina papyracea, as regards both clinical significance and medicolegal reporting. While virtual defects have been reported in the superior semicircular canals as a result of reconstructed images, we believe this to be the first reported case demonstrating a similar problem in the anterior skull base.