Hemifacial Spasm (HFS)

Definition

• Localization in Clinical Neurology, 8e, p. 802
• Adams and Victor's Principles of Neurology, 12th ed.

Epidemiology

• Prevalence: 14.5 per 100,000 in women, 7.4 per 100,000 in men
• Significantly higher prevalence in Asian populations
• Typical onset: 45-52 years (fifth to sixth decade)
• Women > Men
• Most cases are sporadic; rare familial cases exist
• Bradley and Daroff's Neurology in Clinical Practice

Clinical Features

• Begins insidiously in the orbicularis oculi (periorbital twitching)
• Gradually spreads over months to years to involve other ipsilateral muscles: orbicularis oris, buccinator, platysma
• Atypical cases (rare) begin in the orbicularis oris and spread upward

• May be clonic or tonic; often a paroxysm of clonic movements culminates in sustained tonic contraction
• Synchronous in all affected muscles on that side
• Spontaneous but worsened by voluntary facial movement, anxiety, stress, or fatigue

• Ipsilateral stapedius involvement - causes ear clicking
• Ipsilateral facial weakness may develop in chronic cases
• Some patients have regional cranial neuropathy (altered hearing, trigeminal function)
• Bilateral HFS occurs in ~5% of patients, but the two sides are always asynchronous (bilateral synchronous = not HFS)
• When coexistent with trigeminal neuralgia, the condition is called tic convulsif
• Localization in Clinical Neurology, 8e; Bradley and Daroff's Neurology

Etiology and Pathophysiology

Primary Cause

1. Posterior inferior cerebellar artery (PICA)
2. Anterior inferior cerebellar artery (AICA)
3. Vertebral artery
4. Internal auditory artery; veins at the REZ

Less Common Causes (~5% have structural lesion):

• Epidermoid tumor, vestibular schwannoma, meningioma, astrocytoma
• Parotid gland tumors
• Dolichoectatic basilar artery / fusiform aneurysm
• Multiple sclerosis (bilateral alternating HFS reported)
• Arachnoid cysts, lipomas, bony abnormalities
• Chiari type I malformation
• Post-Bell's palsy or traumatic facial nerve injury
• Very rarely: diabetic ketoacidosis, idiopathic intracranial hypertension

Two Competing Pathophysiological Theories

1. Ephaptic (false synapse) theory - compression-induced demyelination at the REZ allows formation of an ephapse. Ectopic activity is generated and conducted antidromically within the nerve fiber. This is the dominant/mainstream theory.
2. Kindling / facial nucleus reorganization theory - aberrant signals arise from the facial nerve nucleus, which undergoes reorganization due to deranged afferent input from the compressed nerve.

• Bradley and Daroff's; Adams and Victor's; Localization in Clinical Neurology

Investigations

• High-resolution MRI (T1- and T2-weighted spin echo or gradient echo with gadolinium) of the posterior fossa - identifies neurovascular compression at the REZ in most patients
• Dedicated sequences: CISS (Constructive Interference in Steady State) or FIESTA are preferred
• CT is less sensitive for soft tissue and vascular detail
• Routine imaging is not always mandatory in typical presentations, but is required before surgical planning

• EMG shows spontaneous activity; lateral spread response (LSR) - stimulating one branch of CN VII produces response in a non-stimulated branch - is a hallmark electrophysiologic marker of HFS and helps confirm the diagnosis
• Intraoperative EMG/LSR monitoring is used during MVD surgery to confirm adequate decompression

Differential Diagnosis

Treatment

1. Botulinum Toxin Injections (First-line)

• Injected into periorbital subcutaneous tissue and other affected muscles
• Produces clinically meaningful improvement in ~100% of patients
• Side effects: mild and transient (ptosis, local weakness)
• Must be repeated every 3-6 months
• Efficacy maintained for at least 15 years of follow-up
• This is the standard of care for most patients

2. Medical Therapy (less effective, now largely superseded)

• Carbamazepine 600-1200 mg/day - controls spasm in ~2/3 of patients
• Baclofen, gabapentin - second-line alternatives
• Clonazepam, anticholinergics - historically used, limited efficacy
• Many patients cannot tolerate medications long-term

3. Microvascular Decompression (MVD - Jannetta procedure)

• Gold standard surgical treatment; posterior fossa exploration with interposition of a pledget (Teflon) between the offending vessel and the facial nerve
• Success rates: ~84-90% of patients achieve excellent/cure result
• Long-term cure rates high (Barker et al., 705 patients, 8-year follow-up: 84% excellent)
• Complications (up to 15%):
  • Facial nerve weakness (sometimes permanent)
  • Sensorineural hearing loss (CN VIII injury)
  • CSF leak (requires tight dural closure)
  • Recurrence (usually within 2 years)
• Fully endoscopic MVD is an emerging approach (see recent systematic review below)

4. Other Surgical Options (historical/secondary)

• Selective destruction of parts of the facial nerve
• Radiofrequency thermocoagulation
• Decompression of the facial canal
• Bradley and Daroff's Neurology; Adams and Victor's

Recent Evidence (2024-2025)

1. Reoperation for residual/recurrent HFS after MVD (Li et al., 2024 - PMID 39414678): Meta-analysis showing that reoperation carries reasonable efficacy with acceptable risk profile in patients with residual or recurrent spasm.
2. Fully endoscopic MVD (Ansari et al., 2025 - PMID 40050528): Systematic review supports endoscopic MVD as a feasible alternative to microscopic approach, with comparable outcomes.
3. HFS due to vertebrobasilar dolichoectasia (Pour-Rashidi et al., 2025 - PMID 40889404): Case series + systematic review on this specific challenging etiology.

Summary Table

Fine Needle Aspiration Cytology (FNAC) - Principles and ENT Applications

Definition and Overview

• Rapid, inexpensive, and well-tolerated
• Minimal complications compared to large-bore Tru-cut or Vim-Silverman needle biopsies
• Can be performed in an outpatient setting
• Does not require general anaesthesia
• Reduces unnecessary surgery by 35-75% in thyroid disease
• Nearly triples the malignancy yield in patients proceeding to surgery
• S. Das: A Manual on Clinical Surgery; Cummings Otolaryngology

Technique

Equipment

• Needle: 22 or 23 gauge (fine needle)
• Syringe: 10-20 mL, tightly fitted to the needle; a syringe holder/pistol gun may be used for single-handed operation
• Sterile gloves, antiseptic swabs, glass slides, fixative (absolute alcohol)

Steps

1. Patient positioning: Comfortable position with the target lesion accessible and stabilized
2. Skin preparation: Clean the overlying skin with antiseptic
3. Stabilization of the lump: The lesion is fixed between the index finger and thumb of the non-dominant hand
4. Needle insertion: The needle is inserted into the lesion without applying negative pressure first
5. Aspiration: Strong negative pressure is applied by withdrawing the plunger; the needle is moved back and forth (fanning motion) within the lesion in 2-3 different directions to sample multiple areas
6. Release of suction: Before withdrawing, suction is released to prevent the aspirate from being sucked into the barrel of the syringe
7. Withdrawal: The needle is withdrawn while maintaining released suction
8. Smear preparation: The needle is detached, air is drawn into the syringe, then needle is reattached and material is expelled onto a glass slide; a smear is made immediately
9. Fixation and staining:
   • Air-dried smears: stained with Giemsa / Diff-Quik (rapid, for on-site assessment)
   • Wet-fixed smears: fixed in absolute alcohol and stained with Papanicolaou (Pap) stain (preferred for detailed nuclear morphology)
   • Cell block preparation can be done from residual material

Ultrasound Guidance

• The lesion is deep, non-palpable, or heterogeneous
• Previous palpation-guided attempts were non-diagnostic
• Targeting a specific component of a complex lesion (e.g., solid area within a cystic nodule)
• US guidance improves overall sensitivity, specificity, and accuracy of the procedure
• KJ Lee's Essential Otolaryngology; Cummings Otolaryngology

General Cytological Assessment

• Cellularity (adequate vs. non-diagnostic)
• Cell type and architecture
• Nuclear features: size, chromatin pattern, nucleoli, mitoses
• Cytoplasmic features
• Background: colloid, lymphocytes, inflammatory cells, necrosis

• Immunocytochemistry (ICC)
• Flow cytometry (lymphoma immunophenotyping)
• FISH / PCR / molecular testing (e.g., BRAF, RAS, RET/PTC for thyroid; HPV status)
• Microbiological culture (TB, fungal)
• PTH assay from aspirate (for parathyroid localization)

ENT-Specific Applications

1. Thyroid Nodules (Most Common ENT Application)

Indications for FNA based on nodule characteristics (ATA Guidelines):

The Bethesda System for Reporting Thyroid Cytopathology (6-category system):

Key points:

• Papillary carcinoma: diagnostic accuracy of FNAC is ~99%, false-positive rate < 1%
• Follicular carcinoma: CANNOT be diagnosed by FNAC alone - capsular/vascular invasion requires histology of the entire specimen
• Hurthle cell neoplasm: same limitation as follicular lesions
• Non-diagnostic aspirates account for ~15% of cases; repeat US-guided FNA is mandatory (a non-diagnostic result must never be interpreted as negative)
• Molecular testing (Afirma, ThyroSeq) can be applied to indeterminate (Bethesda III/IV) aspirates to refine malignancy risk
• Cummings Otolaryngology; KJ Lee's Essential Otolaryngology

2. Salivary Gland Tumors

• Overall sensitivity: 85.5% to 99%
• Overall specificity: 96.3% to 100%
• Diagnostic accuracy higher for benign tumors
• False-negative for malignancy in up to 5% (malignant tumors can yield benign diagnosis)
• Non-diagnostic / inadequate sampling rate: ~5%
• Repeat FNAB after non-diagnostic result: 82% eventual success rate

• Helps plan the extent of surgery (superficial vs. total parotidectomy; need for frozen section)
• Identifies high-grade malignancy requiring wider resection and neck dissection planning
• Avoids surgery in non-neoplastic conditions (sialadenitis, sarcoid, lymphoma)
• US-guided FNAC improves accuracy for non-palpable or deep lobe parotid lesions

• Cummings Otolaryngology, p. 1505-1506

3. Neck Lymphadenopathy / Neck Masses

• Sensitivity: 89-98%
• Helps distinguish among:
  • Reactive lymphadenopathy
  • Metastatic carcinoma (SCC, thyroid, nasopharyngeal)
  • Lymphoma
  • Tuberculous lymphadenitis
  • HPV-associated oropharyngeal malignancy (p16 testing)

Metastatic Carcinoma in Neck Nodes:

• Most common malignant finding in neck nodes in adults over 40
• FNAC identifies squamous cells, adenocarcinoma cells, or poorly differentiated carcinoma
• p16 immunostaining on FNA material identifies HPV-positive oropharyngeal primaries
• EBV in situ hybridization (EBER) can identify nasopharyngeal carcinoma metastasis

Tuberculous Lymphadenitis:

• Smear shows caseous necrosis, epithelioid cell granulomas, Langerhans giant cells
• ZN stain may show acid-fast bacilli (AFB)
• Culture from aspirate material is diagnostic
• FNAC has high sensitivity for TB lymphadenitis in endemic areas

Lymphoma:

• FNAC alone is not sufficient for initial diagnosis of lymphoma
• Architectural pattern and immunophenotyping needed for WHO subclassification
• Accuracy of NHL subclassification by FNAC alone: only 50-70%
• Definitive diagnosis rate with FNAC ± core needle biopsy: ~65-75%
• Exception: Lymphoblastic lymphoma (high-grade, rapidly progressive) can be diagnosed by FNAC + flow cytometry urgently, allowing early initiation of therapy
• When adequate cells are aspirated and flow cytometry + FISH/PCR are combined with cytomorphology, sensitivity/specificity for distinguishing NHL from benign pathology reaches 95-97%
• Current recommendation: FNAC alone is not adequate for initial lymphoma diagnosis; open/core biopsy is preferred for initial workup
• Cummings Otolaryngology (Lymphoma chapter); Bailey and Love's Surgery

4. Parathyroid Glands

• US-guided FNAC with PTH assay from the aspirate is used in re-operative hyperparathyroidism to localize and confirm parathyroid tissue
• PTH level from aspirate is more sensitive than cytology alone because thyroid follicular cells and parathyroid chief cells can look similar on cytology
• Useful in pregnancy when sestamibi scanning is avoided
• Scott-Brown's Otorhinolaryngology

5. Other ENT Applications

Advantages vs. Disadvantages

Advantages

• Rapid (results often same day with rapid staining)
• Outpatient procedure; no anaesthesia required
• Minimal morbidity; very low risk of needle tract seeding (extremely rare with 22-23 G needles)
• Cost-effective; reduces unnecessary surgery by 35-75%
• Tripled malignancy yield in surgical specimens
• Multiple passes possible in the same sitting
• Can be combined with ancillary tests (flow cytometry, molecular testing, culture)

Limitations / Disadvantages

• Cytology only - no tissue architecture (unlike core needle biopsy/open biopsy)
• Follicular carcinoma cannot be distinguished from adenoma - capsular/vascular invasion requires histology
• Lymphoma subclassification is unreliable without architectural context
• Non-diagnostic rate: ~5-15% (sampling error, cystic lesions, fibrotic lesions)
• Highly operator-dependent (skill of aspirator) and interpreter-dependent (cytopathologist experience)
• Vascular lesions (e.g., paraganglioma, hemangioma) - risk of significant bleeding; FNAC is contraindicated in suspected vascular lesions
• Anticoagulated patients: a 2024 systematic review (Ahn et al., PMID 38536462) found FNAC for neck lesions in patients on antithrombotic/anticoagulant medications carries a low but manageable complication risk

Contraindications

• Suspected vascular lesion (paraganglioma, hemangioma, aneurysm) - risk of haemorrhage
• Overlying infected skin (relative contraindication)
• Uncooperative patient (relative)
• Bleeding diathesis (relative; may proceed with caution)
• Known hydatid cyst (risk of anaphylaxis from spillage)

Comparison: FNAC vs. Core Needle Biopsy (CNB) vs. Open Biopsy

Summary: FNAC in ENT at a Glance