Diagnostic Radiology SC022: Imaging Of The Head And Neck Flashcards
Imaging of Neck mass
Considerations:
- Adult / Paediatric (congenital, developmental)
- Acute (infection) / Subacute (neoplasm) / Chronic (benign, congenital)
- Signs of infection?
- Location (upper, lower, midline)
3 main categories:
- Infection
- Cellulitis
- Abscess
- Reactive lymphadenopathy
- Dental infection
- Pharyngitis
- Sialadenitis - Neoplasm
- Malignant lymphadenopathy —> Oorpharyngeal, Nasopharyngeal, Parotid, Cystic nodal metastasis
- Benign —> Schwannoma, Paraganglioma, Lipoma - Congenital
- Branchial cleft cyst, Venous malformation (phleboliths within)
Modality:
- USG
- CT (+/- contrast)
- MRI (+/- contrast)
CT basics
CT: a grayscale representation of attenuation properties of different tissues
Dark (Hypodense / Hypoattenuating) on CT:
- Air
- Fat
Intermediate on CT:
- Soft tissue / Muscle
- Fluid
Bright (Hyperdense / Hyperattenuating (weaken X-ray beam)) on CT:
- Bone / Calcium (Stones)
- Metal
- Contrast
Hounsfield units:
- Quantify attenuation properties of tissues
- Arbitrary scale: Air (-1000), Water (0) —> Everything rated relative to air and water (bone: +1000, lung: -5000, fat: -50, soft tissue, blood: +50)
Radiation dose of Neck CT: 3 mSv (same as annual background radiation dose)
- Chest CT: 7 mSv, Abdomen / Pelvis CT: 14 mSv
- Thyroid is most radiosensitive organ in neck
MRI basics
Bright on T1:
- Fat —> Confirm it is fat with fat suppression
- Blood
- Melanin (melanoma)
- Protein (e.g. colloid cyst)
- Mineralisation
- Gadolinium
Contrast allergy
CT iodinated contrast:
- Premedicate 12 hours before CT (can start 5 hours before if earlier scan required)
—> 12 hours before: Methylprednisolone + Cetirizine
—> 5 hours before: Hydrocortisone + Diphenhydramine
MRI Gadolinium-based contrast:
- Extremely rare
- Could premedicate with Steroid (but no evidence)
Renal disease for contrast
CT iodinated contrast:
- > =30 GFR —> Low risk, little evidence that IV iodinated contrast is independent risk factor for AKI
- **<30 GFR —> Higher risk, do NOT give contrast unless patient on dialysis / anuric / contrast is critical + benefit > risk, document in chart, **IV fluid hydration
MRI Gadolinium-based contrast:
- ***Nephrogenic systemic fibrosis (progressive systemic fibrosis of skin, internal organs —> contractures / fatal)
—> Group 1 agents (e.g. Gadodiamide): NOT use if GFR <30
—> Group 2 agents (e.g. Gadobutrol, Gadoteric acid): May use if necessary when GFR <30
CT / MRI for Pregnancy
Use MRI ***NOT CT for H+N if imaging needed:
- No known risks to fetus with MRI in any trimester —> But generally good practice to avoid MRI in pregnancy if elective / 1st trimester
- Do **NOT give Gadolinium-based contrast —> Gadolinium **teratogenic!!!
Devices CI to MRI
May heat up
- Metallic foreign body in eye (screening orbit CT)
- Gastric reflux device
- Insulin pumps
- Temporary transvenous pacing leads
- Aneurysm clips
- Shrapnel (depending on location —> X-ray / CT)
- Implantable drug infusion pump (conditional)
- Epidural catheters (conditional)
- Feeding tubes (conditional)
- Neural stimulators e.g. VNS, DBS, SCS (conditional)
- Cochlear implants (conditional)
- Pacemaker / ICD (conditional)
Head and Neck infection
CT + Contrast:
- 1st line in acute setting if suspect infection
- Fast (∵ fear of airway compromise if infection)
- Accessible 24/7
- Good resolution (soft tissue, bone e.g. mandible) (can give bone window, soft tissue window)
- Excellent for evaluating infection source / bone (dental disease)
- Deep neck infection (better than USG: only good for superficial structures)
- Emit radiation —> principle of ***ALARA in paediatric group (As Low As Reasonably Achievable)
If there is infection / inflammation in neck —> check ***teeth!!! (∵ dental disease is very common source of infection)
- Other sources: Pharyngitis, Sialolith
Signs of infection:
- Rim-enhancing fluid collection = Abscess (simply fluid —> can be edema)
- Fat stranding (important imaging sign of infection / inflammation)
- Reactive lymphadenopathy (enhancing soft tissue masses)
CT without Contrast
NOT many situations not to order contrast!!!
- Renal disease (GFR <30) (such that contrast may precipitate renal injury)
- Documented contrast allergy + no time to premeditate with ***steroid (need >=5 hours)
Subacute mass
- CT + Contrast
- MRI +/- Contrast —> Good for intracranial / perineural disease
NB:
- New neck mass in **adult **without signs of infection should be considered **malignant **until proven otherwise
- In cases of malignant appearing cervical lymphadenopathy —> report should comment on primary —> important for TNM staging
- A new cystic neck mass in adult should NOT be dismissed as Branchial cleft cyst / Developmental lesion —> Must exclude ***Cystic nodal metastasis (look like cyst) from HPV +ve oropharyngeal SCC
HPV-associated oropharyngeal cancer
- Younger, male mostly, often non-smokers
- HPV: lodges deep within crypts of palatine tonsils, lingual tonsils —> cancers
- Primary cancer in Palatine / Lingual tonsil
—> may be small / ***occult (on both imaging / clinical exam) —> maintain high level of suspicion - Cervical nodes often **cystic —> do NOT assume a new cystic mass in adult is branchial cleft cyst —> must rule out **HPV +ve SCC / ***Thyroid cancer
- Better prognosis than alcohol / tobacco-associated oropharyngeal cancer —> separate AJCC cancer staging system (new)
- Need to know HPV status —> test for ***p16 (kinase inhibitor) —> p16 +ve is a surrogate marker for HPV +ve oropharyngeal cancer
MRI vs CT for tumours of the neck
MRI:
- NPC staging (intracranial, perineural invasion)
- Parotid tumours (perineural spread e.g. CN7)
- Oral cavity tumours (tongue)
- ***Suprahyoid neck in general
- No radiation but young child may require sedation
CT:
- ***Infrahyoid neck in general (e.g. larynx, hypopharynx) (∵ these structures are vulnerable to motions —> MRI takes too long —> motion artefact can obscure lesions)
- Radiation exposure
Carotid body paraganglioma vs Carotid space schwannoma
Paraganglioma: Flow void (indicate blood vessels feeding the tumour)
Schwannoma: No flow void
Branchial cleft abnormalities
- Developmental abnormality from branchial apparatus (which develops into various structures of H+N)
- Failure of branchial cleft to obliterate —> Cyst, Sinus, Fistula
- 4 types (differ in location) —> 2nd type most common
- Often increase in size after vira URTI
Typical location:
- Submandibular gland
- SCM
- Carotid vessels surrounding the cyst
Vascular abnormalities
- USG, MRI (both helpful)
- MRI to visualise full extent (deeper / extensive lesion)
