Head & Neck Cancer
FDG PET/CT for staging, post-chemoradiation surveillance timing, and NI-RADS
Quick Answer
FDG-PET/CT stages head-and-neck squamous cell carcinoma (nodal and distant disease, and occult primaries) and — most importantly for daily practice — guides post-chemoradiation surveillance. A negative PET/CT at the right interval (about 12 weeks after treatment, to let inflammation settle) safely allows surveillance instead of planned neck dissection, as shown in the randomized PET-NECK trial. Structured reporting with NI-RADS standardizes interpretation and follow-up.
Definition
Head-and-neck cancer here refers principally to squamous cell carcinoma (HNSCC) arising from the mucosal epithelium of the oral cavity, oropharynx, larynx, and hypopharynx, plus nasopharyngeal carcinoma (a distinct, EBV-associated entity). Salivary-gland and thyroid cancers are covered separately.
Synonyms
HNSCC; squamous cell carcinoma of the upper aerodigestive tract; oropharyngeal squamous cell carcinoma (OPSCC); nasopharyngeal carcinoma (NPC).
Epidemiology
Two dominant etiologic groups define modern epidemiology: the classic tobacco/alcohol-driven HNSCC (older, often keratinizing, TP53-mutated) and the rising HPV-associated oropharyngeal cancer (younger patients, distinct biology, markedly better prognosis). Nasopharyngeal carcinoma is EBV-associated and endemic in parts of Southeast Asia and North Africa. Incidence and site distribution track regional smoking, alcohol, and HPV prevalence.
Etiology & Risk Factors
- Tobacco and alcohol (synergistic) — classic HNSCC.
- HPV-16 — oropharyngeal (tonsil, base of tongue).
- EBV — nasopharyngeal carcinoma.
- Betel-nut/areca, prior radiation, and occupational exposures (e.g. wood dust — sinonasal).
Pathophysiology
Carcinogen exposure produces field cancerization, explaining synchronous/metachronous second primaries across the aerodigestive tract. HPV-driven cancers act through viral E6/E7 oncoproteins (degrading p53 and Rb), yielding p16 overexpression (an IHC surrogate for HPV) and a more radiosensitive, better-prognosis phenotype. HPV-negative disease is typically TP53-mutated and more aggressive.
Genetics & Molecular Biology
- HPV/p16 status — the single most important prognostic and staging discriminator (AJCC 8th edition stages HPV-positive OPSCC on a separate, more favorable scale).
- TP53 mutation (HPV-negative), CDKN2A loss, EGFR overexpression/amplification, PIK3CA.
- PD-L1 expression guides immunotherapy; EBV DNA (plasma) is a nasopharyngeal biomarker.
Histopathology
Squamous cell carcinoma, ranging from keratinizing (HPV-negative) to non-keratinizing/basaloid (HPV-positive). p16 immunohistochemistry is the routine HPV surrogate. Nasopharyngeal carcinoma is often non-keratinizing/undifferentiated with EBV-encoded RNA positivity.
Clinical Presentation
Neck mass (often the presenting sign), sore throat, dysphagia, odynophagia, hoarseness (glottic), otalgia (referred), and cranial-nerve deficits (nasopharyngeal/skull base). HPV-associated oropharyngeal cancer classically presents as a cystic cervical node with an occult mucosal primary.
Laboratory Findings
No routine serum marker for mucosal HNSCC. p16/HPV on tumor and plasma EBV DNA (nasopharyngeal) are the key molecular tests; PD-L1 for advanced-disease therapy selection.
Imaging Findings by Modality
- Contrast CT / MRI: primary local staging — tumor extent, cartilage/bone invasion, perineural spread (MRI), and nodal mapping.
- FDG-PET/CT: whole-body staging (nodal, distant, second primaries), occult-primary localization, and post-treatment surveillance — the decisive nuclear-medicine role.
- Ultrasound ± FNA: nodal assessment and sampling.
Timing After Chemoradiation
Scanning too early captures treatment-related inflammation and mucositis, producing false positives. The convention is to wait roughly 12 weeks post-treatment, balancing inflammation resolution against not delaying salvage in true residual disease. A negative 12-week PET has a high negative predictive value.
Radiopharmaceutical Uptake Mechanisms
FDG reflects tumor glucose metabolism. Interpretation is dominated by physiologic uptake in muscles (laryngeal, mylohyoid, sternocleidomastoid with tension), lymphoid tissue (Waldeyer ring, palatine/lingual tonsils — often asymmetric), salivary glands, and brown fat, plus post-treatment inflammation — the reason structured, interval-appropriate reading matters.
Typical PET Tracers
| Tracer | Role |
|---|---|
| ¹⁸F-FDG | Staging, occult primary, 12-week post-CRT surveillance |
| (research) ¹⁸F-FMISO / hypoxia tracers | Tumor hypoxia mapping for radiotherapy |
Typical SPECT Tracers
- Sentinel-node lymphoscintigraphy (Tc-99m-sulfur colloid / tilmanocept) for early oral-cavity cancer nodal staging.
- Salivary scintigraphy (Tc-99m-pertechnetate) for post-radiation gland function (see the salivary studies page).
Therapy Indications
- Early disease: single-modality surgery or radiotherapy.
- Locally advanced: concurrent chemoradiation (cisplatin), or surgery with adjuvant (chemo)radiation; cetuximab as a radiosensitizer alternative.
- Recurrent/metastatic: immunotherapy (checkpoint inhibitors by PD-L1) and chemotherapy.
- HPV-positive OPSCC: subject of de-escalation trials aiming to reduce toxicity while preserving the excellent prognosis.
Theranostics
There is no established radioligand therapy for mucosal HNSCC — a useful contrast to prostate/NET disease. The nuclear-medicine contribution is diagnostic and management-defining (surveillance decisions, occult-primary localization), with hypoxia imaging as a research avenue for radiotherapy dose-painting.
Differential Diagnosis (of neck/upper-aerodigestive FDG uptake)
- Physiologic muscle, lymphoid (asymmetric tonsillar), salivary, and brown-fat uptake.
- Post-treatment inflammation/mucositis, infection, and surgical change.
- Second primary aerodigestive cancer (field cancerization) versus metastasis.
- Reactive nodes and granulomatous disease.
Reporting Checklist
- State the interval since chemoradiation (was the ~12-week rule met?).
- Use NI-RADS categories at the primary site and neck, each tied to a management step.
- Report nodal levels, distant sites, and any second primary.
- Explicitly address physiologic/inflammatory mimics and dental-artifact limitations.
NI-RADS (in Practice)
The Neck Imaging Reporting and Data System assigns a suspicion category — 1 (no/low suspicion → routine surveillance), 2 (equivocal → short-interval imaging or direct inspection), 3 (high suspicion → biopsy/intervention), and 4 (known/definite disease) — separately for the primary site and the neck. It standardizes a genuinely hard post-treatment read.
Prognosis
HPV/p16-positive oropharyngeal cancer carries a substantially better prognosis and is staged on a separate favorable AJCC scale. Otherwise, stage, site, smoking history, and nodal burden drive outcome. Post-treatment PET response (and NI-RADS category) is prognostic and guides salvage decisions. Nasopharyngeal outcomes correlate with stage and plasma EBV DNA kinetics.
Board Pearls
NI-RADS category → management (memorize the mapping — it is the actionable core of the post-treatment read):
| NI-RADS | Suspicion | Management |
|---|---|---|
| 1 | No/low | Routine surveillance |
| 2 | Equivocal | Short-interval re-imaging or direct inspection |
| 3 | High | Biopsy / intervention |
| 4 | Known/definite disease | Clinical management as indicated |
A negative FDG-PET/CT at ~12 weeks after chemoradiation has a high negative predictive value and supports active surveillance instead of planned neck dissection (PET-NECK) — imaging earlier captures treatment inflammation and causes false positives. Report with NI-RADS to turn impressions into standardized, actionable categories.
HPV-associated oropharyngeal cancer classically presents as a cystic cervical node with an occult primary — FDG-PET/CT is high-yield for localizing the tonsil/base-of-tongue primary of a neck carcinoma of unknown primary.
The neck is a minefield of physiologic mimics — asymmetric tonsillar/lymphoid tissue, tensed laryngeal/mylohyoid muscle, salivary glands, and brown fat — layered on post-treatment inflammation. Interval-appropriate timing plus NI-RADS discipline is what prevents both false alarms and missed residual disease. Unlike prostate or NET disease, HNSCC has no established theranostic radioligand therapy.
Related Pages
- Disease: Carcinoma of unknown primary (the neck-node/occult-primary overlap).
- Tracer: FDG (preparation, physiologic distribution).
- Related studies: Lymphoscintigraphy & sentinel node (oral cavity), salivary scintigraphy.
Figure / Diagram Suggestions
- A 12-week surveillance timeline showing why earlier imaging over-calls inflammation.
- NI-RADS category → management flow for primary site and neck.
- Annotated physiologic neck uptake plate (tonsils, muscles, salivary, brown fat).
Common Pitfalls
- Osteoradionecrosis of the mandible (and chondroradionecrosis of the larynx) is FDG-avid and closely mimics recurrent tumor — correlate with the radiation field, morphology, and clinical exam.
- Vocal-cord uptake from talking during the uptake phase, or compensatory contralateral cord uptake in unilateral cord paralysis, mimics a laryngeal lesion — enforce voice rest and check for asymmetry.
- Necrotic or cystic (often HPV-positive) nodes may show only faint rim uptake; low central SUV underestimates nodal disease and should not be read as benign.
- Benign FDG-avid salivary lesions — Warthin tumor and oncocytoma — are a classic false-positive in the parotid.
Self-Check (Board-Style)
Q1. Six weeks after chemoradiation, a PET shows diffuse uptake at the primary site and in the neck. How should this be interpreted?
Answer: With caution — imaging at 6 weeks is too early; treatment-related inflammation/mucositis causes false positives. The convention is to wait ~12 weeks for a reliable negative predictive value.
Q2. A young non-smoker presents with a cystic level-II neck node and no visible mucosal primary. What is the likely biology and the high-yield imaging test?
Answer: Likely HPV-associated oropharyngeal carcinoma with an occult tonsil/base-of-tongue primary. FDG-PET/CT is high-yield for localizing the primary and directing biopsy/radiotherapy.
Q3. What does a NI-RADS category 3 at the primary site imply?
Answer: High suspicion for residual/recurrent disease → proceed to biopsy/intervention (as opposed to routine surveillance for category 1 or short-interval imaging for category 2).
Q4. Why does HPV/p16-positive oropharyngeal cancer have its own AJCC staging?
Answer: Its markedly better prognosis means the same anatomic extent corresponds to better outcomes, so it is staged on a separate, more favorable scale than HPV-negative disease.
Evidence & sources
https://nuc.med/head-neck-cancer/ Report an issue