Soft Tissue Neck & Paranasal Sinuses Protocols

Acquisition settings and contrast timings below are illustrative adult protocol examples. Select the authorized protocol for the indication, scanner, body size, access device, and clinical condition. Treatment decisions belong to the responsible clinical team.

Paranasal Sinus CT & FESS Pre-Operative Navigation

Computed tomography of the paranasal sinuses is the pre-eminent imaging examination for evaluating chronic rhinosinusitis refractory to medical therapy, sinonasal polyposis, recurrent acute infections, inverted papillomas, and fibro-osseous lesions. Foremost among its clinical roles is serving as a definitive anatomical roadmap for otolaryngologists performing Functional Endoscopic Sinus Surgery (FESS).

Technical Acquisition & Multiplanar Reconstruction

• Non-Contrast Acquisition: Routine pre-FESS sinus CT is performed without intravenous contrast media, as the primary diagnostic objective is defining bony architecture, drainage pathways, and mucosal thickening against air-filled cavities. Contrast may be indicated for suspected invasive fungal sinusitis, orbital cellulitis, intracranial abscess, or sinonasal malignancies.
• Submillimeter Collimation & Low-Dose Protocols: Acquired using thin submillimeter helical collimation ($0.5\text{ to }1.0\text{ mm}$) from the superior frontal sinuses down through the hard palate. Because the physical contrast between air ($-1000\text{ HU}$) and bone ($>+1000\text{ HU}$) is immense, modern protocols employ low-dose techniques ($100\text{ to }120\text{ kVp}$, $40\text{ to }80\text{ mAs}$), achieving significant radiation reduction without compromising bony resolution.
• Direct Coronal & Sagittal Reformations: Direct coronal reformations perpendicular to the hard palate are vital: the endoscopist views the nasal cavity in the coronal perspective through the endoscope. Multiplanar reformations are displayed using a dedicated Bone Window (WW 2000 to 2500, WL 300 to 400) with an edge-enhancing sharp algorithm, complemented by a soft-tissue series (WW 350, WL 40) to assess mucosal polypoid disease.

The Osteomeatal Complex (OMC)

The osteomeatal complex is the common functional drainage pathway and aerodynamic drainage bottleneck for the anterior group of paranasal sinuses (frontal sinus, anterior ethmoid air cells, and maxillary sinus). Any anatomical distortion or mucosal edema within this narrow crossroad halts mucociliary clearance, resulting in chronic stagnant sinusitis:

1. Maxillary Sinus Ostium: The primary natural drainage opening located high on the superomedial wall of the maxillary sinus.
2. Ethmoid Infundibulum: A narrow, funnel-shaped passage connecting the maxillary ostium to the middle meatus.
3. Uncinate Process: A thin, curved, knife-like mucosal bone leaf running anterosuperior to posteroinferior, forming the medial boundary of the ethmoid infundibulum.
4. Hiatus Semilunaris: The crescent-shaped spatial groove or gap between the uncinate process and the ethmoid bulla.
5. Ethmoid Bulla: The largest, most prominent and constant anterior ethmoid air cell, protruding inferomedially into the middle meatus above the infundibulum.
6. Middle Meatus: The air-filled drainage channel situated beneath the middle nasal concha (turbinate).

High-Risk Surgical Anatomical Variants (The Pre-FESS Checklist)

The otolaryngologist operating with rigid micro-endoscopes works within millimeters of the anterior skull base, orbital contents, and carotid arteries. The CT technologist and radiologist must meticulously identify and report critical surgical hazard variants:

1. Keros Classification of the Olfactory Fossa: Measures the vertical depth of the olfactory fossa—the vertical distance between the cribriform plate of the ethmoid bone and the higher ethmoid roof (fovea ethmoidalis formed by the orbital plate of the frontal bone), determined by the height of the paper-thin lateral lamella of the cribriform plate:
   • Keros Type I ($1\text{ to }3\text{ mm}$ depth): Shallow fossa; the lateral lamella is short and robust. Carries the lowest risk of intracranial penetration.
   • Keros Type II ($4\text{ to }7\text{ mm}$ depth): Intermediate depth; frequency varies across studied populations.
   • Keros Type III ($8\text{ to }16\text{ mm}$ depth): Deep olfactory fossa with an extremely long, delicate, wafer-thin lateral lamella. Major Surgical Hazard: The thin lateral lamella provides limited structural protection to endoscopic micro-debriders. Accidental surgical perforation into the anterior cranial fossa results in dura laceration, substantial cerebrospinal fluid (CSF) rhinorrhea, tension pneumocephalus, frontal lobe laceration, and bacterial meningitis.
2. Lamina Papyracea Dehiscence: The lamina papyracea is the paper-thin bony lateral wall of the ethmoid sinus separating it from the orbit. Dehiscence (focal thinning or congenital/traumatic bone absence) allows orbital fat or the medial rectus muscle to prolapse directly into the ethmoid sinus lumen. If unrecognized, endoscopic resection can transect the medial rectus muscle or tear orbital vessels, causing blindness or acute intraorbital hematoma requiring immediate lateral canthotomy.
3. Onodi (Sphenoethmoidal) Cells: The posterior-most ethmoid air cell that pneumatizes superiorly and laterally over the sphenoid sinus. Extreme Surgical Hazard: The optic nerve ($CN\ II$) and internal carotid artery frequently run directly through or along the lateral wall of an Onodi cell. If the surgeon mistakes an Onodi cell for the sphenoid sinus, instrument insertion into the cell can blind the patient (optic nerve avulsion) or puncture the carotid artery, causing fatal exsanguination.
4. Haller (Infraorbital Ethmoid) Cells: Ethmoid air cells that pneumatize along the medial orbital floor immediately inferior to the ethmoid bulla. When enlarged, Haller cells mechanically compress the maxillary sinus ostium and infundibulum, causing refractory maxillary sinusitis.
5. Concha Bullosa: Extensive pneumatization of the middle nasal concha (turbinate). When massive, it can obstruct the middle meatus and lateral nasal wall.
6. Agger Nasi Cells: The most anterior ethmoid cells located anterior-superior to the attachment of the middle turbinate, forming the anterior floor of the frontal recess.

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Soft Tissue Neck CT Protocols

Computed tomography of the soft tissue neck is the primary diagnostic imaging modality for evaluating mucosal head and neck squamous cell carcinomas (HNSCC) of the oral cavity, pharynx, and larynx; cervical lymphadenopathy; deep neck space infections and abscesses; thyroid and parathyroid pathologies; and salivary gland neoplasms.

Anatomical Coverage Boundaries

• Superior Limit: Skull base / sella turcica (to capture the nasopharynx, retropharyngeal nodes of Rouvière, and sphenoid sinus).
• Inferior Limit: Scanned continuously down to the thoracic inlet and aortic arch (level of T3–T4). Coverage through the thoracic inlet or superior mediastinum may be prescribed for oncologic assessment to evaluate supraclavicular lymph nodes (Level IV/V), paratracheal chains (Level VI), and superior mediastinal nodes (Level VII), A neck acquisition extending to the arch does not exclude a second primary cancer throughout the lungs.

Intravenous Contrast Administration & Timing

Accurate evaluation of the neck requires robust, homogeneous vascular opacification to distinguish enhancing blood vessels (carotid arteries, internal jugular veins) from non-enhancing cervical lymphadenopathy, and to detect the peripheral hypervascular rim enhancement of deep neck abscesses:

• Contrast Protocol: $75\text{ to }100\text{ mL}$ of non-ionic low-osmolar contrast media (LOCM, $300\text{ to }350\text{ mg I/mL}$) administered via a power injector at a flow rate of $2.0\text{ to }3.0\text{ mL/s}$ via an 18- or 20-gauge antecubital catheter, followed by a $40\text{ mL}$ saline flush.
• Scan Delay (Parenchymal / Venous Phase): An illustrative venous-phase delay is $65\text{ to }70\text{ seconds}$.
  • Why Arterial Timing Fails: If scanning begins too early (e.g., $25\text{ to }35\text{ seconds}$, arterial phase), the internal jugular veins are non-uniformly opacified, creating dense swirling flow artifacts that simulate acute thrombosis. Furthermore, cervical lymph nodes and mucosal tumors fail to reach peak parenchymal enhancement, making necrotic nodal metastases blend into surrounding muscular tissues.
  • Split-Bolus Technique: An alternative protocol utilized in select institutions: an initial bolus of $50\text{ mL}$ is injected at $t=0$, followed by a 90-second delay, after which a second bolus of $50\text{ mL}$ is injected at $2.0\text{ mL/s}$, with scanning initiated at $t=110\text{ seconds}$. This achieves simultaneous dense arterial and venous/mucosal enhancement in a single radiation pass.

Patient Motion Artifact Mitigation: The Breathing & Swallowing Mandate

Motion artifacts represent the greatest single obstacle to diagnostic neck CT:

• The Swallowing Prohibition: Swallowing causes rapid, dramatic vertical translation of the hyoid bone, larynx, and pharyngeal musculature by up to $2\text{ to }3\text{ cm}$. If the patient swallows during the scan pass, massive band-like motion streak artifacts radiate across the laryngeal cartilages, obliterating the true vocal cords, epiglottis, and pyriform sinuses. Technologists must deliver strict pre-scan instructions: "Breathe gently through your nose, and DO NOT SWALLOW during the scan."
• Quiet Breathing vs. Breath-Hold: The patient is instructed to breathe quietly. A forced deep inspiration or Valsalva maneuver distorts mucosal landmarks and can induce coughing. For dedicated vocal cord evaluation, phonation protocols ("saying 'eeee' continuously during scan acquisition") may be utilized to adduct the true cords and assess mobility.
• Dental Filling Artifacts: Metallic dental restorations generate severe beam hardening and streak artifacts that obscure the oral cavity, tongue base, and tonsillar pillars. To mitigate this, the patient's head is tilted or the scan plane is angulated when feasible to pass the dental plane separately from the soft palate and oropharynx.

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Cervical Lymph Node Classification (Levels I through VII)

Accurate localization of cervical lymphadenopathy according to the American Joint Committee on Cancer (AJCC) imaging classification system is essential for surgical neck dissection planning and oncologic staging:

1. Level I (Submental and Submandibular Groups):
   • Level IA (Submental): Situated between the medial anterior bellies of the digastric muscles, superior to the hyoid. Drains anterior floor of mouth, lower lip, and tongue tip.
   • Level IB (Submandibular): Bounded by the anterior belly of the digastric medially, the stylohyoid muscle posteriorly, and the body of the mandible laterally. Surrounds the submandibular gland. Drains oral cavity, oral tongue, and lips.
2. Level II (Upper Internal Jugular Chain): Extends from the skull base down to the inferior border of the hyoid bone, bounded anteriorly by the posterior margin of the submandibular gland and posteriorly by the posterior border of the sternocleidomastoid (SCM) muscle.
   • Level IIA: Situated anterior/medial to the spinal accessory nerve ($CN\ XI$) or adjacent to the internal jugular vein.
   • Level IIB: Situated posterior/lateral to the spinal accessory nerve, separated by a thin fat plane.
3. Level III (Middle Internal Jugular Chain): Extends from the inferior border of the hyoid bone down to the inferior margin of the cricoid cartilage ring.
4. Level IV (Lower Internal Jugular Chain): Extends from the inferior margin of the cricoid cartilage down to the superior margin of the clavicle and sternal notch.
5. Level V (Posterior Triangle Group): Bounded anteriorly by the posterior border of the SCM, posteriorly by the anterior margin of the trapezius muscle, and inferiorly by the clavicle.
   • Level VA: Superior to the inferior cricoid cartilage border (spinal accessory nodes).
   • Level VB: Inferior to the cricoid cartilage down to the clavicle (supraclavicular nodes).
6. Level VI (Anterior / Central Visceral Compartment): Extends between the medial margins of the bilateral carotid sheaths, bounded superiorly by the hyoid bone and inferiorly by the suprasternal notch. Contains the prelaryngeal (Delphian), pretracheal, and paratracheal nodes surrounding the thyroid gland.
7. Level VII (Superior Mediastinal Group): Situated below the suprasternal notch between the carotid arteries down to the level of the innominate (brachiocephalic) vein.

Evaluate nodes by more than diameter

Short-axis size, distribution, shape, enhancement, necrosis and surrounding changes inform nodal assessment. A node above a conventional size threshold is not proof of malignancy, and a small node can contain tumor. Central low attenuation can occur in malignant nodes, infection and other processes; it is not 100% specific. Relate each node to the correct cervical level and compare with the primary lesion and prior studies.

Deep Cervical Fascia & Deep Neck Spaces

The soft tissues of the neck are partitioned into distinct compartments by the superficial cervical fascia and the three layers of the deep cervical fascia (DCF): the Superficial (Investing) Layer, the Middle (Visceral) Layer, and the Deep (Prevertebral) Layer. The displacement of fat within these spaces guides accurate differential diagnosis, while fascial planes dictate the route of life-threatening infection spread:

1. Parapharyngeal Space (PPS): A central, paired, fat-filled inverted pyramid extending from the skull base to the greater cornu of the hyoid bone. Its fat is the key radiological landmark of the suprahyoid neck. The direction in which PPS fat is displaced pinpoints tumor origin:
   • Displaced medially: Arises from the masticator space (mandible/masseter) or parotid gland.
   • Displaced anteriorly: Arises from the carotid space (e.g., schwannoma or paraganglioma pushing fat forward).
   • Displaced laterally: Arises from the pharyngeal mucosal space.
2. Masticator Space: Enclosed by the investing layer of the DCF, containing the ramus of the mandible, muscles of mastication (masseter, temporalis, medial and lateral pterygoids), and the mandibular nerve ($V_3$). Common site of odontogenic abscesses.
3. Carotid Space (Carotid Sheath): Extends from skull base to aortic arch. Encloses the common/internal carotid artery, internal jugular vein, vagus nerve ($CN\ X$), and the sympathetic plexus.
4. Retropharyngeal Space (RPS): A potential space situated behind the pharynx and esophagus, between the visceral fascia anteriorly and the alar fascia posteriorly. Extends from the skull base inferiorly to the level of T1 to T4 in the superior mediastinum, where the alar fascia fuses with the visceral fascia.
5. The Danger Space (Space 4): Situated immediately posterior to the retropharyngeal space, between the alar fascia anteriorly and the prevertebral fascia posteriorly. Critical Clinical Hazard: Unlike the retropharyngeal space which terminates at T1–T4, the Danger Space extends continuously from the skull base all the way through the posterior mediastinum down to the level of the diaphragm. Infections originating from odontogenic, tonsillar, or retropharyngeal sources that breach the alar fascia enter the Danger Space, providing a frictionless highway for rapid descending spread into the chest. This produces substantial descending necrotizing mediastinitis, empyema, purulent pericarditis, and septic shock requiring urgent clinical management.
6. Submandibular & Sublingual Spaces: Situated beneath the floor of the mouth, partitioned by the mylohyoid muscle. Rapidly spreading, bilateral cellulitis and gangrene involving both spaces is known as Ludwig's Angina—an emergency causing superior and posterior displacement of the tongue, culminating in fatal upper airway asphyxiation.

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Larynx, neck trauma and targeted parathyroid CT

The larynx contains the supraglottic structures, true vocal folds at the glottis and the subglottic airway below. Thin axial images and coronal reformations show the airway, pre-epiglottic and paraglottic spaces and thyroid/cricoid cartilage. In a mass examination, assess extension and airway compromise; cartilage invasion is not one universal stage across all primary sites. Treatment and formal staging belong to the interpreting and treating teams.

In neck trauma, preserve immobilization and airway support and tailor the ordered acquisition to soft-tissue, vascular or osseous injury. Suspected expanding hematoma or airway compromise requires prompt clinical communication. A routine venous neck examination does not automatically replace a dedicated arterial CTA for vascular injury.

Parathyroid localization CT, often called 4D CT, combines anatomy with enhancement over time. “4D” refers to temporal enhancement behavior, not a fourth spatial axis. The supervising protocol selects unenhanced and contrast-enhanced phases; the number and timing vary. Adenomas may show early enhancement and later washout, but a pattern is not independently diagnostic. Reconstruct thin multiplanar views to relate suspected tissue to thyroid, tracheoesophageal grooves, vessels and ectopic mediastinal sites. Cover the ordered potential ectopic locations, with range and phase count optimized because repeated neck acquisitions add dose. Imaging localizes suspected disease; laboratory assessment establishes hyperparathyroidism.

Reference: ACR parathyroid adenoma imaging criteria.