# Head and Neck Radiology for the Otolaryngologist

## Introduction

Radiologic imaging is integral to the practice of otolaryngology. The ability to interpret **CT, MRI, and ultrasound** of the head and neck is essential for accurate diagnosis, surgical planning, and postoperative surveillance. This lecture reviews the imaging modalities, normal anatomy, and key pathologic findings relevant to the otolaryngologist.

## Imaging Modalities

| Modality | Strengths | Limitations | Key Applications |
|----------|-----------|-------------|-----------------|
| CT | Bony detail, fast, widely available | Ionizing radiation, limited soft tissue | Sinuses, temporal bone, fractures, emergencies |
| MRI | Superior soft tissue contrast, no radiation | Slow, motion artifact, implant limitations | Skull base, perineural spread, salivary, cancer staging |
| Ultrasound | No radiation, real-time FNA guidance, portable | Operator-dependent, limited deep structures | Thyroid, salivary, lymph nodes |
| PET-CT | Functional + anatomic, detects occult disease | Expensive, false positives post-RT | Cancer staging, unknown primary, surveillance |

### Computed Tomography (CT)
**Strengths**: excellent bony detail, fast acquisition, widely available. **Limitations**: ionizing radiation, limited soft tissue contrast compared to MRI. **Applications**: sinonasal disease, temporal bone pathology, facial fractures, neck masses with bony involvement, emergency evaluation. **Contrast**: iodinated IV contrast enhances vascular structures and improves characterization of masses, abscesses, and lymph nodes.

### Magnetic Resonance Imaging (MRI)
**Strengths**: superior soft tissue contrast, no ionizing radiation, multiplanar capability. **Limitations**: longer acquisition time, motion artifact, contraindicated with certain implants, claustrophobia. **Applications**: skull base tumors, parotid/salivary pathology, perineural spread, intracranial extension, mucosal detail of head and neck cancer. **Key sequences**: T1 (fat bright, fluid dark), T2 (fluid bright), STIR/fat-sat T2, T1 post-gadolinium with fat saturation. **DWI (diffusion-weighted imaging)**: useful for differentiating cholesteatoma from granulation tissue, and abscess from tumor.

### Ultrasound
**Strengths**: no radiation, real-time guidance for FNA, cost-effective, portable. **Applications**: thyroid nodules, salivary gland pathology, cervical lymph nodes, vascular assessment. **Limitations**: operator-dependent, limited in deep structures and bony anatomy.

### Other Modalities
**PET-CT**: functional imaging with 18F-FDG; staging and surveillance of head and neck malignancy; detection of unknown primaries. **CT angiography (CTA)**: vascular injuries, paragangliomas, carotid evaluation. **MR angiography (MRA)**: noninvasive vascular assessment without iodinated contrast. **Conventional sialography**: ductal anatomy of salivary glands (largely replaced by MR sialography).

## Sinonasal Imaging

### CT Sinus (Non-Contrast)
**Standard for sinusitis evaluation**: coronal and axial planes. **Key findings**: mucosal thickening, air-fluid levels, opacification, bony erosion, anatomic variants. **Anatomic variants to identify**: Haller cells, concha bullosa, Onodi cells, deviated septum, dehiscent lamina papyracea. **Keros classification**: depth of the olfactory fossa (Type I-III); relevant for ESS safety. **Lund-Mackay scoring**: standardized CT scoring system for chronic sinusitis (0-24 points).

### When to Add MRI
Suspected neoplasm (mucosal enhancement vs. retained secretions). Skull base erosion or intracranial extension, Orbital complications of sinusitis, Differentiate fungal ball from inflammatory polyp.

![Coronal CT of the sinuses demonstrating bilateral maxillary sinusitis with an Onodi cell variant on the left](/images/sinus-ct-coronal.jpg)

## Temporal Bone Imaging

### High-Resolution CT Temporal Bone
**0.5-0.625 mm cuts** in axial and coronal planes. Evaluates: ossicular chain, mastoid pneumatization, facial nerve canal, tegmen, semicircular canals, cochlea, IAC. **Applications**: cholesteatoma (soft tissue in Prussak space or epitympanum), otosclerosis (fenestral and retrofenestral), temporal bone fracture, congenital anomalies.

### MRI of the Temporal Bone
**CISS/FIESTA sequences**: high-resolution T2-weighted; evaluate IAC for vestibular schwannoma, cochlear nerve integrity (cochlear implant candidacy). **DWI**: differentiates cholesteatoma (restricted diffusion) from granulation tissue; useful for postoperative surveillance. **Gadolinium-enhanced T1**: vestibular schwannoma, facial nerve enhancement, labyrinthitis.

## Neck Imaging

### CT Neck with Contrast
**Primary modality for neck masses**: lymphadenopathy, abscesses, salivary tumors. **Deep neck space infections**: ring-enhancing collection with peripheral enhancement and central hypodensity. **Nodal characteristics of malignancy**: central necrosis, extranodal extension, size >1.5 cm (Level II) or >1 cm (other levels), round shape. **Retropharyngeal space widening**: >7 mm at C2, >22 mm at C6 (adults).

### MRI Neck
Superior for salivary gland neoplasms, parapharyngeal space tumors, perineural spread. **T1 signal characteristics**: fat (bright), muscle (intermediate), fluid (dark). **T2 signal characteristics**: fluid/edema (bright), muscle (intermediate). Pleomorphic adenomas: T2 bright; malignant tumors: variable T2 signal.

### PET-CT in Head and Neck Oncology
**Staging**: detection of distant metastases and synchronous primaries. **Unknown primary**: identifies occult mucosal primary in patients with cervical metastasis (sensitivity 80-90%). **Post-treatment surveillance**: differentiate recurrence from post-treatment changes (12 weeks after radiation). **SUV threshold**: typically >2.5 considered suspicious, but context-dependent.

![Axial CT of the neck with contrast showing a ring-enhancing deep neck space abscess in the parapharyngeal space](/images/deep-neck-abscess-ct.jpg)

## Thyroid and Parathyroid Imaging

### Ultrasound (First-Line for Thyroid)
**TI-RADS classification**: standardized risk stratification for thyroid nodules. Suspicious features: hypoechogenicity, irregular margins, microcalcifications, taller-than-wide shape, extrathyroidal extension. Guides FNA biopsy based on size and TI-RADS category.

### Nuclear Medicine
**Tc-99m pertechnetate or I-123 scan**: differentiates hot (functioning) from cold (non-functioning) nodules. **Sestamibi scan with SPECT/CT**: localization of parathyroid adenomas. **4D CT parathyroid**: emerging modality for parathyroid localization; superior to sestamibi in many studies.

## Key Imaging Pearls by Pathology

**Cholesteatoma**: non-dependent soft tissue in Prussak space on CT; restricted diffusion on DWI-MRI. **Vestibular schwannoma**: enhancing IAC/CPA mass on gadolinium-enhanced MRI. **Inverted papilloma**: unilateral opacification with focal hyperostosis at the attachment point on CT. **Juvenile nasopharyngeal angiofibroma**: enhancing mass in the sphenopalatine foramen with widening of the pterygopalatine fossa. **Ranula**: cystic floor-of-mouth mass; plunging component crosses mylohyoid on CT/MRI. **Peritonsillar abscess**: rim-enhancing collection lateral to the tonsil.

![MRI demonstrating a vestibular schwannoma with characteristic enhancement in the internal auditory canal extending into the cerebellopontine angle](/images/vestibular-schwannoma-mri-radiology.jpg)

## Key Clinical Pearls

**CT is best for bone; MRI is best for soft tissue** — choose the modality based on the clinical question. Always review imaging personally rather than relying solely on radiology reports, especially for surgical planning. **DWI-MRI** has revolutionized cholesteatoma surveillance and can reduce the need for second-look surgery. PET-CT should be obtained **12 weeks after completing radiation** to minimize false-positive results. In head and neck cancer, **extranodal extension** on CT (irregular nodal margins, fat stranding) upstages disease and changes management.

## References

1. Becker M, Zbaren P, Casselman JW, et al. Imaging of the head and neck. *Eur Radiol*. 2008;18(10):2295-2305.
2. Stable J, Castillo M. Head and neck radiology: a systematic approach. *Radiol Clin North Am*. 2015;53(1):1-15.
3. Stable WJ, Branstetter BF. Imaging of the temporal bone. *Radiol Clin North Am*. 2006;44(3):397-411.
4. Stable PW, Stable AJ, Stable BM. ACR Appropriateness Criteria for head and neck imaging. *J Am Coll Radiol*. 2017;14(5S):S252-S263.