Thyroglossal cyst differentials
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Differentials of Thyroglossal Duct Cyst (TDC)
A thyroglossal duct cyst (TDC) is the most common congenital cystic mass of the neck and the second most common benign neck mass after lymphadenopathy. It typically presents as a painless midline swelling that moves up on both swallowing AND tongue protrusion - the latter being the pathognomonic feature, as the thyroglossal duct runs from the foramen caecum to the thyroid isthmus. Differentials are best organized by midline vs. lateral position, then by characteristics.
Midline Neck Differentials (the most relevant group)
| Condition | Key Distinguishing Features |
|---|---|
| Dermoid Cyst | Also midline, also moves with tongue protrusion if attached to hyoid bone; doughy/putty consistency (sebaceous content); does NOT transilluminate; often suprahyoid; no tongue protrusion movement if not attached |
| Subhyoid Bursitis | Lies directly over the hyoid bone; fluctuant; moves with swallowing but NOT with tongue protrusion; no epithelial lining |
| Ectopic/Lingual Thyroid | Midline mass at base of tongue or along thyroglossal tract; NO normal thyroid tissue below on USS; can be the ONLY thyroid tissue - must confirm with imaging before any excision |
| Pyramidal Lobe of Thyroid / Goitre | Moves with swallowing; connected to thyroid gland; does NOT move with tongue protrusion; firm; thyroid tissue on USS |
| Enlarged Submental Lymph Node | Firm, discrete, often multiple; reactive to infection; does NOT move with tongue protrusion |
| Lipoma | Soft, lobulated, non-tender; does NOT move with swallowing or tongue protrusion; dull on percussion |
| Pre/Paratracheal Lymph Node | Firm, may be multiple; no tongue protrusion movement |
| Ludwig's Angina | Acute onset, diffuse, bilateral submandibular/sublingual space; systemic features of infection; woody-hard |
| Sebaceous Cyst | Skin-deep, attached to overlying skin (punctum present); no movement with swallowing or tongue protrusion |
| Thymic Cyst | Rare; suprasternal midline; extends into mediastinum; confirmed on CT/MRI |
| Ranula | Sublingual; fluctuant; transilluminates; "plunging ranula" can appear in midline submental region |
Key Clinical Pointer: The Tongue Protrusion Test
"The pathognomonic feature is that [the TDC] moves upwards with protrusion of the tongue since the thyroglossal duct extends downwards from the foramen caecum of the tongue to the isthmus of thyroid gland."
- S Das, Manual on Clinical Surgery
However, Bailey and Love cautions: "Classically, the cyst moves upwards on swallowing and with tongue protrusion, but this can also occur with other midline cysts such as dermoid cysts, as it merely indicates attachment to the hyoid bone." - Bailey & Love's Short Practice of Surgery, 28th ed.
Most Important Differential to Exclude: Ectopic Thyroid
As noted in Sabiston and Bailey & Love: a TDC-appearing mass may represent an incompletely descended thyroid containing the only functioning thyroid tissue. Inadvertent excision would render the patient permanently hypothyroid. Preoperative USS (or thyroid scan) to confirm a normal orthotopic thyroid is mandatory before surgery.
Cystic Differential Summary (by type)
Cystic chronic midline swellings:
- Thyroglossal cyst
- Dermoid cyst
- Cystic hygroma (more lateral/posterior triangle, but can be anterior)
- Sebaceous cyst
- Cold abscess (fluctuant, pointing, associated with TB)
Solid midline swellings:
- Thyroid goitre (isthmus/pyramidal lobe)
- Ectopic thyroid
- Lymphoma
- Branchiogenic carcinoma
Imaging Summary
On USS, TDCs appear as anechoic cystic masses with posterior wall enhancement infrahyoid; may be pseudosolid if proteinaceous. There is a ~1% incidence of papillary thyroid carcinoma within TDC - solid components on imaging should raise suspicion. - Scott-Brown's Otorhinolaryngology, Head & Neck Surgery
Cranial nerve examination
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I now have comprehensive material from Harrison's, Goldman-Cecil, Rosen's Emergency Medicine, and Neuroanatomy through Clinical Cases. I have everything needed for a thorough answer.
Cranial Nerve Examination
There are 12 cranial nerves (CN I-XII). They are examined in numerical order, with CN III, IV, and VI grouped together due to their shared function in eye movement.
CN I - Olfactory Nerve
Function: Smell
How to test:
- Ask the patient to close their eyes
- Occlude one nostril at a time
- Present a non-pungent, familiar odorant (coffee, toothpaste, vanilla) to each nostril separately
- Ask them to identify the smell
Abnormality: Anosmia (loss of smell)
Clinical note: Often omitted in routine examination; test when inferior frontal lobe pathology is suspected (e.g., meningioma, head injury, early Parkinson's, COVID-19 sequelae)
CN II - Optic Nerve
Function: Vision
How to test:
| Test | Method |
|---|---|
| Visual acuity | Snellen chart at 6 metres, with correction if worn; near vision card for bedside |
| Visual fields | Confrontation testing - examiner sits 1 metre away, tests each eye individually; moves finger in all 4 quadrants; check for hemianopia, quadrantanopia |
| Pupillary light reflex | Direct and consensual responses (afferent = CN II, efferent = CN III) |
| RAPD (Marcus Gunn pupil) | Swinging flashlight test - if afferent defect exists in one eye, the pupil dilates rather than constricts when light swings to that eye |
| Fundoscopy | Examine optic disc (colour, margins, cup:disc ratio), retinal vessels, macula |
Key findings: Optic disc swelling (papilloedema = raised ICP), pale disc (optic atrophy), visual field defects localise the lesion along the visual pathway
CN III, IV, VI - Oculomotor, Trochlear, Abducens
Functions:
- CN III (Oculomotor): Elevates upper lid; moves eye up, down, medially; constricts pupil (parasympathetic); elevates lid (levator palpebrae)
- CN IV (Trochlear): Intorsion and depression of eye (superior oblique) - tested by asking patient to look down and in
- CN VI (Abducens): Lateral gaze (lateral rectus)
How to test:
- Pupils - size, shape, symmetry at rest; direct and consensual light reflex; accommodation reflex (convergence + pupil constriction)
- Ptosis - look for drooping of upper lid (CN III palsy, Horner syndrome)
- Eye movements - ask patient to follow your finger in an "H" pattern without moving their head; test all 6 positions of gaze
- Nystagmus - note direction of fast phase; observe at 45° lateral gaze (not extreme lateral); hold position for several seconds
Key findings:
- CN III palsy: "Down and out" eye, ptosis, dilated fixed pupil (if complete - surgical CN III palsy, e.g., PCA aneurysm compressing parasympathetic fibres on outside of nerve)
- CN IV palsy: Vertical diplopia worse on looking down and in; patient tilts head to opposite side
- CN VI palsy: Failure of abduction (lateral rectus palsy); horizontal diplopia; commonest false localising sign in raised ICP
- Horner syndrome (sympathetic): Miosis + ptosis + anhidrosis (not a direct CN palsy but clinically important)
CN V - Trigeminal Nerve
Functions: Sensation to face (3 divisions); motor to muscles of mastication
Sensory testing - 3 divisions:
- V1 (Ophthalmic): Forehead, cornea, anterior scalp
- V2 (Maxillary): Cheek, upper lip, upper teeth
- V3 (Mandibular): Lower lip, chin, lower teeth, anterior two-thirds of tongue (general sensation only)
Test light touch (cotton wool) and pain/temperature (pin or cold) in all 3 divisions on both sides - these travel in different anatomical pathways.
Motor testing:
- Ask patient to clench teeth - palpate masseters bilaterally
- Ask to open mouth against resistance - pterygoids; jaw deviates toward the weak side in pterygoid weakness
Reflexes:
- Corneal reflex: Touch cornea with cotton wisp - blink response uses CN V (afferent) and CN VII (efferent). Loss of corneal reflex with intact sensation = CN VII lesion; loss with reduced sensation = CN V lesion
- Jaw jerk: Tap chin with patient's mouth slightly open; brisk = UMN lesion above pons; absent = normal or LMN
CN VII - Facial Nerve
Function: Motor to muscles of facial expression; taste (anterior 2/3 tongue via chorda tympani); lacrimation; stapedius (hyperacusis)
How to test:
- Inspect face at rest - look for asymmetry, flattening of nasolabial fold
- Ask to: raise eyebrows, wrinkle forehead, close eyes tightly, show teeth, puff cheeks, whistle
Critical UMN vs. LMN distinction:
| Feature | UMN Lesion (cortex/internal capsule) | LMN Lesion (nerve, nucleus) |
|---|---|---|
| Forehead | Spared (bilateral cortical innervation) | Affected (complete ipsilateral weakness) |
| Lower face | Contralateral weakness | Ipsilateral weakness |
| Eye closure | Preserved | Weak (Bell's phenomenon visible) |
| Taste/lacrimation | Preserved | May be lost |
| Examples | Stroke, tumour | Bell's palsy, parotid tumour, Ramsay Hunt |
"Weakness of the lower two-thirds of the face with preservation of the upper third suggests an upper motor neuron lesion, whereas weakness of an entire side suggests a lower motor neuron lesion." - Harrison's Principles of Internal Medicine, 22nd ed.
CN VIII - Vestibulocochlear Nerve
Function: Hearing (cochlear division); balance (vestibular division)
How to test:
| Test | Method | Interpretation |
|---|---|---|
| Whisper test | Whisper 2-syllable words/numbers 60 cm from each ear | Screens for significant hearing loss |
| Finger rub | Rub fingers near each ear | Simple bedside screen |
| Rinne test | 512 Hz tuning fork: mastoid (bone) then near ear (air) | Normal / sensorineural: AC > BC; Conductive: BC > AC |
| Weber test | 512 Hz tuning fork on centre of forehead | Lateralises to affected ear (conductive) or away from affected ear (sensorineural) |
Note: Rinne and Weber only performed if hearing loss is detected. Formal audiometry for any suspected abnormality.
CN IX & X - Glossopharyngeal & Vagus Nerves
Functions:
- CN IX: Taste and sensation posterior 1/3 tongue; stylopharyngeus; carotid sinus reflex
- CN X: Palatal and laryngeal motor; visceral autonomic; sensation from pharynx/larynx
How to test:
- Inspect the palate at rest - look for asymmetry or uvular deviation
- Ask patient to say "Ahh" - palate should rise symmetrically; uvula deviates away from the paralysed side (the intact side "pulls" it)
- Gag reflex: Stimulate posterior pharyngeal wall with tongue blade; CN IX = afferent, CN X = efferent; note - may be absent in normal individuals
- Listen for hoarseness or nasal quality of voice (vagal palsy)
- Ask about difficulty swallowing or regurgitation of fluids
Key findings: Unilateral vagal palsy - hoarse voice, fluid regurgitation through nose, uvular deviation away from lesion side
CN XI - Spinal Accessory Nerve
Function: Motor to sternocleidomastoid (SCM) and trapezius
How to test:
- Trapezius: Ask patient to shrug both shoulders; resist downward pressure - weakness causes ipsilateral shoulder droop
- SCM: Ask patient to turn head to each side against resistance; SCM contracts on the contralateral side (turning head right = left SCM contracts); weakness causes inability to turn head away from the lesion side
CN XII - Hypoglossal Nerve
Function: Motor to all intrinsic and extrinsic muscles of the tongue
How to test:
- Inspect tongue at rest in floor of mouth - look for fasciculations or wasting
- Ask patient to protrude tongue - note deviation
- Test strength by asking patient to press tongue against inner cheek; resist from outside
Key findings:
| Lesion | Tongue appearance | Deviation on protrusion |
|---|---|---|
| UMN (contralateral cortex) | Normal bulk | Deviates toward weak (contralateral) side |
| LMN (nerve itself) | Wasting + fasciculations (ipsilateral) | Deviates toward lesion side |
"Lower motor neuron lesion causes the tongue to deviate toward the side of the lesion, and the affected side atrophies over time." - Rosen's Emergency Medicine
Quick Reference Summary Table
| CN | Name | Function | Key Test | Key Reflex |
|---|---|---|---|---|
| I | Olfactory | Smell | Odour identification | - |
| II | Optic | Vision | Snellen, fields, fundoscopy | Pupillary light (afferent) |
| III | Oculomotor | Eye movement, pupil | H-test, pupil response | Pupillary light (efferent) |
| IV | Trochlear | Eye depression/intorsion | Look down and in | - |
| V | Trigeminal | Face sensation, mastication | Cotton wool, pin, jaw clench | Corneal (aff), Jaw jerk |
| VI | Abducens | Lateral gaze | H-test | - |
| VII | Facial | Facial expression, taste | Raise brow, close eyes | Corneal (eff) |
| VIII | Vestibulocochlear | Hearing, balance | Rinne, Weber, finger rub | - |
| IX | Glossopharyngeal | Taste posterior tongue, gag | Gag reflex | Gag (afferent) |
| X | Vagus | Palate, voice, viscera | Palate rise ("Ahh") | Gag (efferent) |
| XI | Spinal accessory | SCM, trapezius | Shoulder shrug, head turn | - |
| XII | Hypoglossal | Tongue | Protrusion, fasciculations | - |
Sources: Harrison's Principles of Internal Medicine 22nd ed.; Rosen's Emergency Medicine; Goldman-Cecil Medicine; Neuroanatomy through Clinical Cases 3rd ed.
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