EurAsia Group Researchers Introduce New CT-Based Classification to Guide Frontal Sinus Surgery

Goran Latif Omer
2 days ago
4 min read

Frontal sinus surgery remains one of the most technically demanding procedures in endoscopic sinus surgery. The frontal recess, the narrow pathway leading to the frontal sinus, varies considerably between patients and lies close to critical structures including the orbit, skull base, and anterior ethmoidal artery. Even small anatomical differences can therefore influence surgical access, instrument selection, and operative complexity.

Preoperative CT imaging is essential for understanding this anatomy. However, most existing classification systems focus primarily on identifying anatomical structures and frontal recess cells. They provide less information about a more practical surgical question: how accessible is the frontal sinus, and what instruments may be required to reach it safely?

In a newly published study, EurAsia Group researchers and international collaborators introduced a CT-based classification designed specifically to address this gap. The system evaluates two surgically important anatomical features: the nasofrontal beak (NFB) and frontal ostium clearance (FOC).

The nasofrontal beak is the bony structure forming the anterior boundary of the frontal sinus opening. Frontal ostium clearance represents the available working space between the tip of this bone and the skull base. Together, these measurements provide an indication of the bony corridor through which surgeons must work during frontal sinus surgery.

Developing the Classification from More Than 2,500 Frontal Sinuses

The study was conducted in two phases.

In the first phase, researchers retrospectively analysed CT scans from 1,383 patients, representing 2,595 frontal sinuses. A standardised CT measurement technique was developed to determine the anteroposterior length of the nasofrontal beak and the available frontal ostium clearance.

Analysis of the measurements identified natural anatomical groupings around 6 mm and 12 mm, which were supported by histogram analysis, kernel density estimation, and unsupervised K-means clustering.

The nasofrontal beak was subsequently divided into three classes:

Class A: 6 mm or less
Class B: 6 to 12 mm
Class C: 12 mm or greater

Frontal ostium clearance was classified in the opposite direction because a larger clearance represents easier access:

Class A: 12 mm or greater
Class B: 6 to 12 mm
Class C: 6 mm or less

This created a simple measurement-based system in which Class A generally represents more favourable surgical anatomy, while Class C represents a longer nasofrontal beak or narrower working corridor.

The CT measurement technique also demonstrated excellent reproducibility. Assessment by eight independent raters produced an intraclass correlation coefficient of 0.988, indicating very high agreement between observers.

Taking the Classification into the Operating Room

The second phase prospectively evaluated the system in 100 patients undergoing frontal sinus surgery, representing 191 frontal sinuses.

CT-based measurements were compared with direct intraoperative findings, allowing the researchers to examine whether the anatomical classes seen on preoperative imaging corresponded to what surgeons encountered during surgery.

The nasofrontal beak classification showed the stronger radiological-to-surgical relationship, with an overall classification accuracy of 68.1% and a quadratic-weighted Cohen's kappa of 0.55. Frontal ostium clearance showed more modest agreement, with an overall accuracy of 61.3%.

These findings led the researchers to recommend prioritising the nasofrontal beak classification when the NFB and FOC classes do not correspond.

Importantly, the study was designed to demonstrate anatomical-surgical concordance and feasibility, rather than to claim that the classification improves outcomes compared with existing approaches. As a single-centre study, further multicentre validation will be necessary before the proposed cut-offs can be adopted more broadly.

Linking CT Anatomy to Surgical Instruments

One of the most practical features of the proposed classification is its connection to instrument selection.

For patients with a Class A nasofrontal beak, the frontal sinus could generally be visualised without altering the beak, with conventional angled endoscopes providing adequate access.

For Class B anatomy, the posterior two-thirds of the nasofrontal beak could be shortened using a frontal sinus punch to improve access.

For the more challenging Class C anatomy, a straight or curved drill was used to remove a greater portion of the nasofrontal beak and create sufficient access to the frontal sinus.

Endoscope requirements also followed the anatomical classification. Class A anatomy could generally be assessed using 0° to 30° optics, while Class B and particularly Class C cases more frequently required 45° and 70° endoscopes.

The system therefore attempts to move CT interpretation beyond anatomical description and towards operative preparation, allowing surgeons to anticipate the type of access and instrumentation that may be required before entering the operating room.

Complementing Existing Frontal Sinus Classifications

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

Instead, the two approaches address different questions. IFAC helps surgeons understand the arrangement of frontal recess cells, while the new NFB and FOC system focuses on the dimensions of the working corridor and their potential implications for instrumentation.

Used together, they may provide a more complete understanding of both the anatomical configuration and the practical accessibility of the frontal sinus.

An International Research Collaboration

The project brought together researchers and surgeons from institutions in Iraq, Italy, and the United States, reflecting a broad international collaboration in advanced rhinology and frontal sinus surgery.

The research team included Dr. Goran Latif Omer, Dr. Sahand Soran Ali, Prof. Mario Turri-Zanoni, Prof. Paolo Battaglia, Prof. Iacopo Dallan, Dr. Andrea Gravina, Prof. Giuseppe De Donato, Prof. Paolo Castelnuovo, Prof. Roy R. Casiano, and Prof. Stefano Di Girolamo.

The participating institutions included 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 Preoperative Planning

The study provides a new way of translating CT anatomy into practical surgical information. By measuring the nasofrontal beak and the available frontal ostium clearance, surgeons may be able to anticipate difficult anatomy, select appropriate endoscopes and instruments, and approach frontal sinus surgery with a more structured preoperative plan.

The authors stress that the classification remains a planning adjunct rather than a replacement for comprehensive anatomical assessment, and that external validation involving multiple centres and surgeons will be important.

The paper, “From Imaging to Instrument: A CT-Based Classification of the Nasofrontal Beak and Frontal Ostium Clearance with Prospective Surgical Correlation,” was published on 14 July 2026 in the open-access journal Surgeries, which has an impact factor of 1.5 and a CiteScore of 1.8.