A New CT-Based Classification for Frontal Sinus Surgery: From Imaging to Instrument Selection

Frontal sinus surgery remains one of the most technically challenging areas of endoscopic sinus surgery. The frontal recess is narrow, highly variable between patients, and located close to critical structures including the orbit, skull base, and anterior ethmoidal artery. For this reason, even relatively small anatomical differences can substantially affect surgical access and the instruments required during an operation.

In a recently published study, Dr. Goran Latif Omer and an international team of collaborators introduced a new CT-based classification of the nasofrontal beak and frontal ostium clearance, with the aim of translating preoperative imaging into more practical surgical planning.

The study, titled “From Imaging to Instrument: A CT-Based Classification of the Nasofrontal Beak and Frontal Ostium Clearance with Prospective Surgical Correlation,” was published in the open-access journal Surgeries in July 2026.

From Anatomy to a Practical Surgical Classification

Preoperative CT is already fundamental to frontal sinus surgery. Existing systems, however, generally focus on identifying frontal recess cells and describing anatomical relationships rather than quantifying the actual bony corridor available to the surgeon.

The new classification focuses on two measurements with direct surgical relevance.

The nasofrontal beak (NFB) is the bony structure forming the anterior boundary of the frontal sinus ostium. Its anteroposterior length can influence how easily the frontal sinus can be accessed.

The frontal ostium clearance (FOC) represents the available working space between the tip of the nasofrontal beak and the skull base. A narrower clearance provides less space for instrumentation and may therefore increase the technical demands of surgery.

The researchers developed a standardised CT method for measuring both parameters and then grouped each measurement into three anatomical classes.

For the nasofrontal beak:

• Class A: 6 mm or less

• Class B: 6 to 12 mm

• Class C: 12 mm or greater

For frontal ostium clearance:

• Class A: 12 mm or greater

• Class B: 6 to 12 mm

• Class C: 6 mm or less

In practical terms, Class A generally represents more favourable access, while Class C corresponds to a longer nasofrontal beak or a narrower frontal ostium corridor.

A Two-Phase Study of Nearly 2,800 Frontal Sinuses

The study was conducted in two phases.

The first phase analysed CT scans from 1,383 patients, representing 2,595 frontal sinuses. Measurements of the nasofrontal beak and frontal ostium clearance were examined statistically to determine whether natural anatomical groups could be identified.

The 6 mm and 12 mm thresholds were supported by multiple analytical approaches, including histograms, kernel density estimation, and K-means clustering.

The measurement system also showed excellent reproducibility. Eight independent raters assessed a subset of CT scans, producing an intraclass correlation coefficient of 0.988, indicating very high agreement between observers.

The second phase prospectively included 100 patients undergoing frontal sinus surgery, representing 191 frontal sinuses. CT classifications were compared with direct intraoperative measurements to determine how closely preoperative imaging reflected the anatomy encountered during surgery.

Connecting CT Findings to Surgical Technique

A central aim of the study was to make the classification useful beyond radiological description.

The different nasofrontal beak classes were linked to specific surgical techniques and instruments.

With a Class A nasofrontal beak, the frontal sinus could generally be visualised without modifying the beak.

For Class B anatomy, shortening of the posterior portion of the nasofrontal beak using a frontal sinus punch was typically sufficient to improve access.

For Class C anatomy, where the beak was longer and access more restricted, straight or curved drilling was used to enlarge the surgical corridor.

The type of endoscope required also followed this anatomical progression. Class A cases could often be visualised using 0° or 30° optics, while increasingly angled 45° and 70° endoscopes were more commonly required in Class B and Class C cases.

This creates a direct connection between the preoperative CT scan and a practical question for the operating surgeon: what instruments are likely to be required to access this frontal sinus?

Prospective Surgical Correlation

The nasofrontal beak classification demonstrated the stronger relationship between CT and intraoperative anatomy.

Overall accuracy for CT-based NFB classification was 68.1%, with a quadratic-weighted Cohen's kappa of 0.55. Frontal ostium clearance showed more variable intraoperative measurement, with an overall classification accuracy of 61.3% and a quadratic-weighted kappa of 0.50.

Because the nasofrontal beak is a more stable bony landmark and could be measured more consistently, the study recommends prioritising the NFB class when the two measurements produce different classifications.

The results should not be interpreted as evidence that the system reduces complications or produces superior surgical outcomes. The prospective component was designed to examine anatomical-surgical concordance and feasibility rather than to compare the classification against another surgical strategy.

Complementing Existing Frontal Sinus Anatomy Systems

The proposed system is not intended to replace established classifications such as the International Frontal Sinus Anatomy Classification (IFAC).

IFAC remains important for identifying frontal recess cells and understanding their anatomical relationships. The NFB and FOC classification instead addresses a different aspect of surgical planning by quantifying the available working corridor and connecting those measurements with potential instrumentation.

The two approaches can therefore be considered complementary: one defines the anatomy, while the other helps translate that anatomy into operative planning.

International Collaboration in Frontal Sinus Surgery

The study was led by Dr. Goran Latif Omer, in collaboration with researchers and surgeons from several international institutions.

The author group included Sahand Soran Ali, Mario Turri-Zanoni, Paolo Battaglia, Iacopo Dallan, Andrea Gravina, Giuseppe De Donato, Paolo Castelnuovo, Roy R. Casiano, and Stefano Di Girolamo.

The collaboration brought together expertise from the University of Sulaimani, American University of Iraq Sulaimani, University of Rome Tor Vergata, University of Insubria, Azienda Ospedaliero-Universitaria Pisana, and the University of Miami Miller School of Medicine.

Towards More Structured Frontal Sinus Planning

Frontal sinus surgery cannot be reduced to two measurements, and a complete understanding of frontal recess anatomy remains essential. Nevertheless, the proposed classification offers a simple, reproducible way of adding an instrument-oriented dimension to routine CT evaluation.

By identifying a short, intermediate, or long nasofrontal beak and estimating the available frontal ostium clearance before surgery, the system may help surgeons anticipate the technical requirements of each case and prepare the appropriate instruments and optics in advance.

Further multicentre studies involving different surgeons and patient populations will be required to externally validate the classification and determine how broadly the proposed thresholds can be applied.