CBCT for Chronic Rhinosinusitis: How Cone Beam Imaging Supports FESS Planning and Sinus Assessment

CBCT chronic rhinosinusitis imaging gives ENT surgeons the sub-millimetre sinonasal detail they need before functional endoscopic sinus surgery (FESS). Until recently, traditional medical CT remained the default choice for pre-operative sinus assessment. However, cone beam computed tomography now offers comparable bony resolution at a fraction of the radiation dose. At 3Beam Imaging Centre, 86 Harley Street, our Planmeca ProMax delivers a 20 x 17 cm field of view that captures the full paranasal sinus anatomy in a single acquisition. Specifically, this article explains how CBCT chronic rhinosinusitis assessment supports safer, more precise FESS planning for referring ENT surgeons.

Quick Answer: When Is CBCT Chronic Rhinosinusitis Imaging Indicated?

The 2025 AAO-HNS Clinical Practice Guideline on the Surgical Management of Chronic Rhinosinusitis recommends that surgeons obtain a fine-cut CT scan of the paranasal sinuses before proceeding to FESS. CBCT satisfies this requirement. Specifically, it delivers coronal, axial, and sagittal reformats with isotropic voxel sizes as small as 0.075 mm. For most CRS patients who have failed maximum medical therapy, CBCT chronic rhinosinusitis imaging provides a radiation-efficient route to the anatomical road map that FESS demands.

In particular, CBCT is well suited when the clinical question centres on bony anatomy: ostiomeatal patency, ethmoid partitioning, skull base height, and the relationship of the optic nerve and internal carotid artery to the posterior ethmoid and sphenoid. It is less appropriate when soft-tissue contrast is the primary concern, such as staging intracranial or intraorbital complications of acute sinusitis.

What CBCT Chronic Rhinosinusitis Imaging Reveals for FESS Planning

Successful FESS depends on the surgeon knowing exactly what lies behind the next bony partition. Indeed, CBCT chronic rhinosinusitis scans map the structures that matter most.

Ostiomeatal complex (OMC). The OMC is the functional bottleneck of the anterior sinuses. Notably, CBCT visualises the uncinate process, ethmoid infundibulum, hiatus semilunaris, and maxillary sinus ostium in sub-millimetre detail. Consequently, the surgeon can determine whether OMC obstruction is mucosal, polypoid, or structural before entering the nose.

Ethmoid labyrinth. The anterior and posterior ethmoid air cells vary significantly between patients. Furthermore, CBCT delineates each cell boundary, including Agger nasi cells, Haller (infraorbital) cells, Onodi (sphenoethmoidal) cells, and supraorbital ethmoid cells. Most importantly, identifying an Onodi cell is critical because it brings the optic nerve into the surgical field at an unexpected level.

Skull base and fovea ethmoidalis. The Keros classification grades the depth of the olfactory fossa from Type I (1 to 3 mm) to Type III (8 to 16 mm). Significantly, a deep Keros III fossa raises the risk of skull base penetration during ethmoidectomy. CBCT renders the lateral lamella of the cribriform plate with sufficient clarity to classify Keros type on every scan.

Frontal recess. The frontal recess is the most anatomically variable part of the anterior ethmoid. Then, CBCT sagittal reformats trace the drainage pathway from the frontal sinus through the recess into the middle meatus. This information guides the surgeon in deciding between a Draf I, IIa, IIb, or III frontal sinusotomy.

Lamina papyracea. The medial orbital wall is paper-thin in many patients. Equally, CBCT identifies dehiscences or bowing of the lamina papyracea that could predispose to orbital fat prolapse during surgery.

CBCT vs Medical CT for Sinus Assessment: Dose, Resolution, and Access

ENT surgeons often ask whether CBCT is an acceptable alternative to multidetector CT (MDCT) for pre-FESS imaging. The evidence supports CBCT for most CRS indications.

Radiation dose. Published data show that the mean effective dose for paranasal sinus CBCT ranges from 0.17 to 0.27 mSv. In comparison, standard MDCT sinus protocols deliver 0.5 to 0.87 mSv. Therefore, CBCT reduces the dose by approximately 40 to 70 percent while maintaining diagnostic bony detail.

Spatial resolution. CBCT systems achieve voxel sizes of 0.075 to 0.2 mm. Standard MDCT typically reconstructs at 0.5 to 0.625 mm slice thickness. As a result, CBCT provides finer osseous detail for structures like the lateral lamella, uncinate attachment, and posterior ethmoid septa.

Soft-tissue contrast. MDCT outperforms CBCT for soft-tissue discrimination. If the clinical question involves suspected mucocoele extension, orbital abscess, or intracranial complication, MDCT (or MRI) remains the appropriate modality. For routine pre-FESS anatomical mapping, this limitation is rarely relevant.

Access and speed. At 3Beam, same-day appointments are available including Saturdays. The scan itself takes approximately 20 seconds. Images are available immediately for review. In contrast, NHS MDCT appointments for CRS often carry waiting times of several weeks.

Key Anatomical Landmarks CBCT Identifies Before FESS

A structured approach to reviewing CBCT chronic rhinosinusitis scans ensures no critical landmark is overlooked. The following checklist reflects standard pre-FESS reporting practice.

Anterior skull base. Assess the Keros type bilaterally. Note any asymmetry in fovea height, which increases the risk of inadvertent penetration on the lower side.

Anterior ethmoidal artery. Generally, the artery runs along the skull base between the second and third ethmoid lamellae. CBCT identifies whether it courses through a bony mesentery (suspended below the skull base) or within the skull base itself. Obviously, a suspended artery is more vulnerable during surgery.

Posterior ethmoid and sphenoid. Look for Onodi cells and assess the relationship of the optic nerve canal and internal carotid artery to the sphenoid sinus walls. Particularly, CBCT shows bony dehiscence over these structures, which the surgeon must know about before dissection.

Maxillary sinus. Confirm the position of the natural ostium relative to the inferior turbinate. Also assess for accessory ostia, antrochoanal polyps, or infraorbital nerve (Haller) cells that narrow the infundibulum.

Frontal sinus. Evaluate the anteroposterior diameter of the frontal recess on sagittal views. Identify any frontal cells (Kuhn Type I to IV) that could obstruct the drainage pathway. For more detail on matching the field of view to your clinical question, see our guide to CBCT field of view selection.

Nasal septum. Finally, document any septal deviation, spur, or perforation that might require concurrent septoplasty or that could impede endoscopic access.

How CBCT Chronic Rhinosinusitis Scans Support the Lund-Mackay Score

The EPOS 2020 position paper and the 2025 AAO-HNS guideline both reference the Lund-Mackay scoring system for objective CT-based disease assessment. The score grades opacification in each of the anterior ethmoid, posterior ethmoid, maxillary, frontal, and sphenoid sinuses bilaterally (0 = clear, 1 = partial, 2 = total), plus the ostiomeatal complex (0 = not occluded, 2 = occluded). The maximum score is 24.

Research confirms that CBCT chronic rhinosinusitis imaging provides reliable Lund-Mackay grading. Studies comparing high-dose and reduced-dose CBCT protocols found equivalent pathology scores (mean 4.95 vs 5.26), demonstrating that dose-optimised CBCT maintains diagnostic accuracy for disease quantification.

Importantly, the 2025 AAO-HNS guideline advises against planning the extent of surgery solely on Lund-Mackay scores or arbitrary opacification thresholds. Instead, the score should be interpreted alongside symptoms, endoscopy findings, and response to medical therapy. CBCT supports this integrated approach by providing the anatomical context that pure scoring cannot capture.

When to Choose CBCT Over Medical CT for Sinus Disease

Not every CRS patient needs CBCT. Similarly, not every patient needs MDCT. The choice depends on the clinical question.

CBCT is appropriate when:

• The primary question is pre-FESS anatomical mapping (OMC, ethmoid labyrinth, skull base, frontal recess)
• The patient has already had a diagnostic nasal endoscopy confirming CRS and the next step is surgical planning
• Dose reduction is a priority (for example, younger patients or those who have already undergone multiple imaging studies)
• Rapid access is needed and NHS MDCT waiting times are a barrier to timely surgery

MDCT or MRI is more appropriate when:

• Soft-tissue detail is essential (suspected orbital or intracranial complication, invasive fungal sinusitis, sinonasal tumour staging)
• The imaging is the primary diagnostic step before endoscopy (MDCT provides broader soft-tissue context)
• Contrast-enhanced imaging is required

For cases where the clinical picture suggests a dental origin of sinus symptoms, our article on CBCT for odontogenic sinusitis covers the specific imaging considerations. Additionally, when incidental findings arise in sinus CBCT scans, our guide to CBCT incidental findings outlines the reporting and referral pathway.

How 3Beam Supports ENT Sinus Referrals

3Beam Imaging Centre operates a dedicated ENT and sinus scanning service from 86 Harley Street. Our Planmeca ProMax 3D system captures the entire sinonasal anatomy, including the frontal sinuses, in a single 20 x 17 cm field of view. Scan time is approximately 20 seconds, and images are available for immediate review.

Where requested by the referrer, every CBCT includes a formal report from a UK Dental Radiologist. The structured report covers all the pre-FESS landmarks discussed in this article: Keros classification, OMC status, ethmoid cell variants, skull base integrity, lamina papyracea, and frontal recess anatomy. Referrers receive the report and DICOM dataset, typically within 24 hours.

ENT surgeons can refer patients using our ENT referral form or by calling 0207 637 8227. Same-day and next-day appointments are available, including Saturdays.

Frequently Asked Questions

Q: Does CBCT chronic rhinosinusitis imaging replace the need for nasal endoscopy?
A: No. CBCT and nasal endoscopy provide complementary information. Endoscopy shows the mucosal surface, polyp burden, and discharge patterns in real time. CBCT reveals the underlying bony anatomy and disease extent beyond what the endoscope can reach. Both are recommended before FESS.

Q: Can CBCT detect nasal polyps?
A: CBCT demonstrates sinus opacification and can show polypoid mucosal thickening. However, it does not differentiate polyp tissue from other causes of mucosal disease as effectively as MDCT or MRI. Therefore, polyp diagnosis is best confirmed by endoscopy.

Q: Is CBCT suitable for revision sinus surgery planning?
A: Yes. In revision cases, CBCT is particularly valuable because it shows residual bony partitions, neo-osteogenesis, and altered anatomy from previous surgery. The sub-millimetre resolution helps identify landmarks that may have been disrupted.

Q: How does the radiation dose of sinus CBCT compare to a chest X-ray?
A: A sinus CBCT at 3Beam delivers approximately 0.2 mSv, which is comparable to a single chest radiograph (approximately 0.02 mSv for PA only, or 0.1 mSv for PA and lateral). It is significantly lower than a standard MDCT sinus scan (0.5 to 0.87 mSv).

Q: Do I need to justify a CBCT referral under IR(ME)R 2017?
A: Yes. All CBCT referrals in the UK require clinical justification under the Ionising Radiation (Medical Exposure) Regulations 2017. For CRS patients who have failed medical therapy and are being considered for FESS, pre-operative anatomical imaging is a well-established clinical indication.

The Bottom Line on CBCT Chronic Rhinosinusitis

CBCT chronic rhinosinusitis imaging delivers the osseous detail that FESS demands at a substantially lower radiation dose than conventional MDCT. It maps the ostiomeatal complex, ethmoid labyrinth, skull base, and frontal recess with sub-millimetre precision. For ENT surgeons planning FESS in patients who have failed maximum medical therapy, CBCT provides a rapid, low-dose, high-resolution alternative to hospital-based CT. At 3Beam, same-day sinus CBCT with structured radiologist reporting is available six days a week from 86 Harley Street.