CT in Head & Neck Cancer

Michelle A. Michel, MD

Key Facts

Clinical Implications

CECT: Best initial modality for patient presenting with neck mass of uncertain etiology
Fast; good-quality imaging is readily reproducible
Less affected by breathing & swallowing artifacts than MR in infrahyoid neck/mediastinum
Superior for detecting cortical bone erosion & intratumoral calcification
Helpful for determining tumor extent & size, identifying nodal disease, assessing response to therapy, & restaging
CT also useful for image-guided biopsy
Preferred imaging modality for tumors of oropharynx, hypopharynx, & larynx
Tumor volume measurements with CT correlate with local control & outcome for supraglottic, glottic, pyriform sinus, & nasopharyngeal carcinoma

Imaging Approaches

MDCT: Scan from sella to thoracic inlet or to carina
Coronal & sagittal reconstructions aid in determining tumor extent

Special Techniques/Dynamic Maneuvers

“Puffed cheek”
Modified Valsalva
Phonation
Open mouth
3D endoscopic view

Risk Factors & Complications

Contrast reactions are uncommon, particularly with use of nonionic, low osmolality agents
Patients with renal insufficiency, dehydration, & paraproteinemias are at increased risk for contrastinduced nephropathy (CIN)

(Left) Axial CECT in a patient with left neck mass shows necrotic bilateral level II lymph nodes

. Primary SCCa is seen arising from the lower pole of the left palatine tonsil

. (Right) Axial CECT shows supraglottic SCCa

involving left paraglottic space. CT is preferred modality for imaging laryngeal cancers as it is less affected by motion artifacts. Although normal by size criteria, the small left III lymph node

shows prominent enhancement and was pathologic on biopsy.

(Left) Axial CECT shows classic maxillary SCCa. CT shows extension into soft tissues of cheek

. In this case, margin of the mass can be distinguished from low-density secretions

trapped behind the tumor. (Right) Axial bone CT in the same patient shows the bone destruction to better advantage. The tumor grossly destroys the anterior

and posterior

maxillary sinus walls. Although not subtle in this case, CT is superior for evaluating cortical bone involvement.

TERMINOLOGY

Definitions

• CT: Fundamental cross-sectional imaging modality for evaluating H&N cancer

CLINICAL IMPLICATIONS

Clinical Importance

CECT is best initial modality for patient presenting with neck mass of uncertain etiology
CECT is excellent modality for SCCa staging
- Determining tumor extent & size, identifying nodal disease, assessing response to therapy, & evaluating for recurrent disease
- Preferred by many for determination of pathologic lymph nodes
- CT is superior for detecting cortical bone erosion & intratumoral calcification
- Preferred imaging modality for tumors of oropharynx, hypopharynx, & larynx
- Fast & less affected by breathing & swallowing artifacts in infrahyoid neck/mediastinum
- Better detail of parathyroid glands than MR (less affected by breathing & pulsation artifacts)
- Good quality imaging readily reproducible

IMAGING APPROACHES

Multidetector Computed Tomography (MDCT) with Multiplanar Reformations

CECT with coverage from skull base to thoracic inlet required for SCCa staging; to evaluate left recurrent laryngeal nerve course, coverage must extend through carina
High-quality, thin-slice images reconstructed in multiple planes from single data set
- Permits high-resolution images unaffected by movement
- Decreased scan time allows for reduced contrast dose
- Minimizes radiation exposure
  - Bismuth shields may be used to ↓ thyroid & lens exposure
  - Slight neck extension allows exclusion of orbits
NECT with bone algorithm may be performed after MR in nasopharyngeal & oral cavity tumors to identify cortical bone invasion

Reformatted Images

Sagittal & coronal reformations are very helpful for assessing craniocaudal extent of hypopharyngeal, laryngeal, & tracheal lesions
Allows 3rd plane measurement of mass or nodes
Coronal
- Identifies skull base & orbital invasion
- Assesses transglottic extension of laryngeal tumors
Sagittal
- Best identifies invasion of preepiglottic fat by tongue base & supraglottic tumors

IMAGING PROTOCOLS

Neck

Craniocaudal helically acquired sections obtained from skull base (sella) through carina
- Coverage through carina necessary for evaluation of left true vocal cord (TVC) dysfunction
- Slice thickness ˜ 0.6-1.25 mm
- Head positioned with beam parallel to inferior orbitalmeatal line with no gantry tilt
- Additional scans angled above maxillary and below mandibular dentition to exclude amalgam artifact
- Images reconstructed with standard (soft tissue) algorithm & edge-enhancing (bone) algorithm
  - Soft tissue = ww 350/wl 40; 2.5 mm
  - Bone = ww 3,000/wl 800; 0.625-1.25 mm
- Other parameters: kVp = 120; mA range = 100-800; gantry rotation time ˜ 0.7 sec (↑ for larger patients); beam collimation = 20 mm; detector configuration = 32 × 0.625; pitch ˜ 1; table speed ˜ 20 mm/rotation
- Perform with patients in quiet respiration, not holding breath
Contrast
- Standard recommended dose = 90-120 mL
  - Standard dose administered if GFR > 60
  - Tissue enhancement affected by body weight (weight-adjusted dose recommended for higher body weights)
  - < 80 mL contrast (1.3 mL/kg with iodine concentration of 300 mg/mL) results in suboptimal vessel contrast
- Contrast rate ˜ 2 cc/sec after ˜ 60 second scan delay
- Split bolus technique for contrast administration may improve lesion/vascular enhancement
- Saline chaser technique (40 mL saline added on top of contrast in injector)
  - Clears IV catheter of contrast & keeps tighter contrast bolus
  - Avoids pooled contrast in arm veins, reducing perivenous artifacts
  - May not show any difference in neck vessel attenuation (arterial vs. venous)
- Side of injection may have little effect on mean attenuation value in vessels

Sinonasal

Thin-slice axial data set acquired with MDCT and reconstructed in coronal ± sagittal planes
Coronal reformations performed perpendicular to hard palate, extending from nasal vestibule through sella
- Reformat thickness: 1.0-1.5 mm
Sagittal reformations performed perpendicular to hard palate
Typically performed without contrast unless there is contraindication to gadolinium-enhanced MR for precise tumor mapping

Specific Techniques/Dynamic Maneuvers

“Puffed cheek”
- Improves visualization of oral cavity mucosal tumors along the typically apposed surfaces (gingival & buccal mucosa/oral tongue & gingivae)
- Cheeks, gingivae, lips, buccal vestibule, buccinator muscle, pterygomandibular raphe, and retromolar trigone better delineated
- Patient blows uniformly through pursed lips
  - 1 mm thick scans performed from hard palate to inferior edge of mandible
  - Optimized by moving tongue away from hard palate & teeth
Modified Valsalva
- Used to improve evaluation of location & extent of hypopharyngeal tumor due to apposition of mucosal surfaces or nasopharyngeal lesions when pharyngeal recesses (fossa of Rosenmüller) are collapsed
- Opens the glottis & distends the laryngeal vestibule & pyriform sinuses; improves separation of postcricoid & postarytenoid soft tissues from posterior pharyngeal wall
- True & false cords are abducted and poorly depicted
- Patient breathes out against resistance of pursed lips (for hypopharynx) or a pursed nose (for nasopharynx)
  - 1 mm thick scans performed from hyoid bone to trachea
  - Patient training improves success of maneuver
Phonation
- Used when true & false vocal cords are not clearly depicted (apposed) when scan performed during apnea or quiet respiration
- True & false cords and laryngeal ventricles better depicted
- Improves accuracy of determining supraglottic vs. glottic tumors
- Patient says “eeeeeeeee” for 10 seconds
  - 1 mm thick scans performed from hyoid bone to trachea
  - Patient training improves success of maneuver
Open mouth
- Used to improve visibility of oral cavity & oropharynx masses obscured by dental amalgam artifact
- Improves visualization of soft palate, cheeks, gingivae, mobile tongue
- Avoids “missing” areas and double irradiation of areas in the common procedure of tilting scanner gantry to avoid amalgam
- Patient opens mouth, and device (e.g., 50 mL syringe) is placed between teeth for stabilization
  - 1-3 mm thick scans obtained from maxilla to mandible in quiet respiration
3D endoscopic view
- “Virtual endoscopy”: High-resolution volumetric images processed to provide 3D rendering of mucosal surfaces
- Evaluates airway narrowing beyond a stricture not accessible via endoscopy
- Most helpful for evaluation of laryngotracheal stenosis
- Noninvasive, typically does not require sedation or IV contrast
  - Evaluation of pediatric subglottic stenosis post intubation
- 3D reconstructions processed using surface- or volume-rendered techniques
- Best for evaluating extent & shape of subglottic & tracheal stenosis
  - May overestimate stenosis at level of glottis due to adduction of vocal cords

CLINICAL INDICATIONS & UTILITY BY REGION

Role of CT in H&N Cancer Patient

Initial staging
- Evaluate size & extent of primary lesion
- Tumor volume measurements correlate with local control & outcome for supraglottic, glottic, pyriform sinus, & nasopharyngeal carcinoma
  - CT also helpful for identifying synchronous or metachronous neoplasms
  - Hypopharyngeal primaries most likely to have 2nd primary (1/3 synchronous with initial SCCa)
- Assess for nodal involvement
- Identify metastases: Lung apices, bone, thyroid
Image guidance for biopsy
- Directs to most accessible & highest yield site for tissue sampling
Treatment planning (type of surgery, radiation fields, ± chemotherapy)
- CT helps to determine resectability of T4 lesions
- Critical factors that should be sought on imaging
  - Tracheal & esophageal extension, laryngeal cartilage invasion, preepiglottic fat involvement
  - Bone invasion: Mandible, maxilla, & skull base
  - Dural spread, perineural tumor spread, orbital invasion, & brachial plexus invasion
  - Arterial encasement, prevertebral fascia involvement, mediastinal infiltration
Assess response to therapy & potential complications
- Baseline imaging after therapy used to assess for residual tumor & serves as roadmap for future studies
  - Performed 8-10 weeks post chemoradiation, 10-12 weeks post surgery
Surveillance
- Variable frequency of follow-up studies (3- to 6-month intervals)
- Compare to baseline examination to detect recurrent disease & re-stage
- Recurrence most often in 1st 2 years post treatment