A Computed Tomography (CT) scan uses X-rays and computer processing to create detailed cross-sectional pictures of the body’s internal structures. When a CT scan is ordered specifically for the sinuses, its primary focus is the air-filled cavities within the face and skull. Although the standard protocol prioritizes upper facial anatomy, the physical area covered almost always includes the very top part of the throat, known as the nasopharynx. Other throat structures, such as the oropharynx and the voice box (larynx), are typically located outside the focused scan area and are usually not fully or clearly visualized.
Primary Focus of Paranasal Sinus CT
The main purpose of a paranasal sinus CT is to evaluate the four pairs of major sinus cavities: the maxillary, frontal, ethmoid, and sphenoid sinuses. These scans are most frequently performed to diagnose and evaluate conditions like chronic sinusitis. The CT provides a clear picture of the bony walls and air spaces, helping physicians identify blockages, fluid collection, or growths like nasal polyps.
This imaging protocol is optimized to distinguish between air, bone, and soft tissue within the nasal cavity and the sinuses. The high-resolution images are particularly useful for mapping the complex anatomy of the ostiomeatal unit, which is the common drainage pathway for the frontal, maxillary, and anterior ethmoid sinuses. Detailed visualization of these structures is paramount when planning for functional endoscopic sinus surgery (FESS).
By focusing on bone and air, the scan helps to quickly identify anatomical variations that might predispose a person to sinus problems, such as a deviated nasal septum or an enlarged middle turbinate. A non-contrast study is generally sufficient for these diagnostic purposes, as the goal is to look at the air-filled spaces and the surrounding bone rather than the blood flow within soft tissues.
Defining the Scan Field of View
The Field of View (FOV) is the physical area selected by the technician to be included in the CT image, and this parameter determines what parts of the throat are incidentally captured. For a standard sinus CT, the scan range typically extends from the top of the frontal sinuses down to the floor of the maxillary sinuses or the hard palate. This vertical range is chosen to encompass all the paranasal sinuses and the nasal passage.
Because the scan extends downward through the nasal cavity, it naturally includes the nasopharynx, the uppermost section of the throat located directly behind the nose and above the soft palate. This area is often visible because it falls within the cone of X-ray beams necessary to image the posterior sinuses, such as the sphenoid sinus. Therefore, the nasopharynx is usually well-visualized on a sinus CT.
The scan is intentionally limited in its downward extent to minimize unnecessary radiation exposure to the neck and lower structures. The oropharynx, which contains the tonsils and the back of the tongue, and the hypopharynx and larynx (voice box) are located below the typical caudal boundary of the sinus protocol. These lower structures usually fall outside the focused FOV, meaning they are either partially excluded or are only seen at the very edge of the image where image quality may be compromised.
The slice thickness and resolution are also optimized for the fine bony architecture of the sinuses, not the dense soft tissues of the lower throat. Standard sinus protocols often use very thin slices, which is excellent for bone detail but can result in a more limited vertical coverage compared to a dedicated neck scan.
Dedicated Imaging for Throat Structures
When a comprehensive evaluation of the lower throat is required, a standard sinus CT is inadequate due to its limited coverage and technical settings. The structures of the lower pharynx and larynx are best imaged using a distinct protocol known as a “CT Soft Tissue Neck” or “CT Neck.” This dedicated scan is specifically designed to visualize the oropharynx, hypopharynx, larynx, and the surrounding soft tissues and lymph nodes.
A primary difference in the neck protocol is the routine use of intravenous (IV) contrast material, an iodine-based dye injected into a vein during the scan. This contrast agent enhances blood vessels and highlights masses, infections, or enlarged lymph nodes, which is important for diagnosing many conditions found in the lower throat. In contrast, the standard sinus CT is most often performed without any contrast material, as the primary targets are air and bone.
The technical parameters of a CT Neck are optimized for soft tissue resolution, allowing better differentiation between muscles, glands, and potential masses. The scan extent is significantly broader, often running from the base of the skull down to the top of the chest, ensuring full coverage of the voice box and surrounding neck structures. This positioning and coverage allows for the detection of conditions such as vocal cord paralysis, thyroid abnormalities, or cancerous masses that originate in the tonsils or larynx.
If a physician suspects a problem in the oropharynx or larynx based on symptoms like persistent hoarseness or difficulty swallowing, they will order the dedicated CT Neck scan. The differences in patient positioning, scan boundaries, and the frequent use of contrast material make the neck protocol a specialized tool for evaluating the soft tissue anatomy of the lower throat.