A Sinus Computed Tomography (CT) scan uses X-rays and computer processing to create detailed cross-sectional images of the paranasal sinuses and surrounding structures. This diagnostic tool is frequently used to investigate chronic sinusitis or to assess structural anomalies like a deviated septum. The CT scan provides superior visualization of bone and soft tissue interfaces.
Understanding the Image Views and Orientation
A Sinus CT scan presents the anatomy in a series of digital slices, reconstructed into three primary viewing planes. The axial view is a horizontal slice, cutting the head from top to bottom. The coronal view slices the head from front to back and is useful for assessing drainage pathways. The sagittal view offers a side-to-side profile of the nasal and sinus anatomy.
Understanding the orientation is necessary to correctly map the findings. Standard radiology convention displays images as if the viewer is looking at the patient’s feet. The patient’s right side appears on the left side of the image, and the left side appears on the right. Most digital images include an ‘L’ or ‘R’ marker to indicate the patient’s side. The coronal plane is often the most informative for sinus pathology, as it clearly visualizes the ostiomeatal complex.
Identifying the Major Sinus Structures
The four main paired paranasal sinuses should appear black on a healthy CT scan because they are filled with air:
- Maxillary sinuses, the largest, located in the cheekbones.
- Frontal sinuses, positioned within the forehead bone, above the eyes.
- Ethmoid sinuses, a cluster of small air cells situated between the eyes.
- Sphenoid sinuses, located deepest, behind the nasal cavity and ethmoid cells.
CT scans use different shades of gray to represent tissue density: air is black, bone is bright white, and soft tissues or fluid are various shades of gray. The thin bony walls separating the sinuses should be sharply defined and bright white. Normal sinus mucosa, the tissue lining the interior, is typically invisible, allowing the air-filled cavity to appear uniformly black.
The Ostiomeatal Complex (OMC) is the functional drainage unit for the frontal, maxillary, and anterior ethmoid sinuses. This complex network includes the uncinate process, the ethmoid bulla, and the middle meatus. Patency of the OMC, meaning it is open and clear, is a major indicator of sinus health. Blockage of this region due to inflammation or structural variation is often the underlying cause of chronic sinus disease.
Recognizing Signs of Sinus Disease
Pathology is recognized by material denser than air, appearing as shades of gray or white instead of black. Mucosal thickening is a common finding where the normally thin sinus lining swells due to inflammation. This appears as a circumferential gray layer along the bony walls of the sinus cavity.
Another distinct sign of acute inflammation is an air-fluid level, which presents as a straight horizontal line within a sinus cavity. This line indicates the surface where air rests above a collection of fluid or pus, suggesting acute bacterial sinusitis. Chronic inflammation can lead to complete opacification, where the entire sinus cavity is filled with fluid and thickened mucosa, appearing uniformly gray or white.
Nasal polyps and mucous retention cysts are visible as soft tissue masses. Retention cysts are usually dome-shaped, fluid-filled structures often considered incidental findings in the maxillary sinus. Polyps are extensive soft tissue growths, appearing as bulging, lobulated masses that may completely fill and remodel the sinus cavity.
In long-standing chronic sinusitis, the CT scan may show bony thickening of the sinus walls, a process called osteitis, resulting from prolonged inflammation. Signs like bony destruction or erosion of the sinus walls suggest more aggressive or invasive processes. This is a significant finding that requires immediate clinical attention.
Deciphering the Radiology Report
The radiology report organizes findings to communicate the radiologist’s interpretation. The report begins with the Technique section, detailing how the scan was performed, followed by the Clinical Indication, which states the reason for the exam. The Findings section provides a detailed description of the images, translating visual abnormalities into specific medical terminology.
An observation of a deviated septum points to an off-center nasal wall. The final section, the Impression or Conclusion, summarizes the most significant findings and provides a concise diagnosis or differential diagnosis. This conclusion guides the physician in determining the next steps for patient management and treatment.