Head and Neck Spaces in ENT

A Comprehensive 20-Mark Answer (MS ENT / PG Level)

INTRODUCTION

I. CERVICAL FASCIAE - THE FRAMEWORK

A. Superficial Cervical Fascia

• Envelops the platysma and muscles of facial expression
• Extends from the zygomatic arch superiorly to the clavicle inferiorly
• Acts as the main plane of resistance to deep spread of cellulitis
• Allows skin mobility over deep neck structures

B. Deep Cervical Fascia - Three Layers

• Envelops trapezius, sternocleidomastoid, strap muscles, submandibular and parotid glands, muscles of mastication (masseter, pterygoids, temporalis)
• Extends from mandible/zygoma superiorly to clavicle, acromion, and spine of scapula inferiorly
• Forms the stylomandibular ligament posteriorly (separates parapharyngeal and submandibular spaces)
• Splits anteroinferiorly to form the suprasternal space of Burns
• Outlines the masticator space superiorly

• Muscular division: envelops strap muscles
• Visceral division: pharynx, larynx, trachea, esophagus, thyroid, parathyroid, buccinator, pharyngeal constrictors
• Extends from base of skull to mediastinum
• Forms pretracheal fascia anteriorly
• Forms buccopharyngeal fascia over the pharyngeal wall (this is the anterior border of the retropharyngeal space)

• Envelops paraspinous muscles and cervical vertebrae
• Extends from base of skull to coccyx
• Comprises two sub-layers:
  • Prevertebral layer: attaches to transverse processes, covers vertebral bodies, paraspinous and scalene muscles
  • Alar layer: covers cervical sympathetic trunk, extends from skull base to mediastinum
• The space between the alar and prevertebral layers is the danger space

• Formed from contributions of all three layers of deep cervical fascia
• Envelops: common carotid artery, internal jugular vein (IJV), vagus nerve (CN X)
• Extends from skull base to thorax

II. THE MAJOR HEAD AND NECK SPACES

• Suprahyoid spaces (above hyoid)
• Infrahyoid spaces (below hyoid)
• Spaces spanning both regions

SUPRAHYOID SPACES

1. Parapharyngeal Space (PPS) - The Pivotal Space

• Inverted pyramid (or "ice-cream cone") shape
• Extends from the petrous temporal bone (skull base) superiorly to the hyoid bone inferiorly
• Bilateral symmetry; triangular configuration on axial imaging; hourglass shape on coronal imaging

• Superior: base of skull (middle cranial fossa)
• Inferior: hyoid bone
• Anterior: pterygomandibular raphe
• Posterior: prevertebral fascia
• Medial: pharyngobasilar fascia (superiorly), superior pharyngeal constrictor
• Lateral: deep lobe of parotid gland, mandible, medial pterygoid

• Pre-styloid lesion: displaces carotid sheath and PPS fat posteromedially (e.g., deep parotid lobe tumour)
• Post-styloid lesion: displaces PPS fat anteriorly (e.g., carotid body tumour, vagal schwannoma)

• Spread from the submandibular space (oro-dental source)
• Spread from the peritonsillar space
• Presents with medial displacement of tonsil and lateral oropharyngeal wall, trismus (pterygoid muscle involvement), and may or may not have neck swelling

2. Retropharyngeal Space (RPS)

• Lies between the two parapharyngeal spaces (communicates with both)
• Located posterior to the pharyngeal mucosal space, anterior to the prevertebral space, medial to the carotid space

• Anterior: buccopharyngeal fascia (overlying pharyngeal constrictors)
• Posterior: alar layer of prevertebral fascia

• Nodes of Rouvière (lateral retropharyngeal nodes) - classic; relevant to ENT malignancy staging
• Medial retropharyngeal nodes
• Up to 1 cm considered normal in children; >5 mm is suspicious in adults

• Primary pathway for spread of infection from neck to mediastinum (and vice versa)
• Retropharyngeal abscess: more common in children (2-4 years) due to active lymph nodes; causes dysphagia, muffled voice, neck stiffness, bulging posterior pharyngeal wall; can cause airway obstruction by anterior displacement of the airway
• In adults, RPS involvement with retropharyngeal LN enlargement should raise suspicion of head and neck malignancy (SCC with nodal metastasis)
• Mass in RPS displaces PPS anterolaterally

3. The Danger Space (Space 4 / Alar Space)

• Located posterior to the retropharyngeal space
• Between the alar fascia (anteriorly) and the prevertebral fascia (posteriorly)
• Extends from the skull base all the way down to the diaphragm
• Normally only visible on imaging if distended
• Named "danger space" because infections in the neck can track via this space into the posterior mediastinum as far as the diaphragm, causing life-threatening descending necrotizing mediastinitis

4. Prevertebral Space

• Posterior to the prevertebral fascia, anterior to the vertebral column and paraspinal musculature
• Contains: prevertebral, scalene and paraspinal muscles; brachial plexus; phrenic nerve; vertebral body; vertebral artery and vein

• Infection may result from traumatic pharyngeal perforation (foreign body, endoscopy) or breach of prevertebral fascia from retropharyngeal infection
• Can cause spinal osteomyelitis and spinal cord compression
• In head and neck malignancy, prevertebral space invasion signifies inoperable disease

5. Masticator Space

• Formed by the superficial layer of deep cervical fascia
• Contains: muscles of mastication (masseter, medial and lateral pterygoid, temporalis), ramus and posterior body of mandible, inferior alveolar nerve and vessels
• Infection source: odontogenic (especially lower 3rd molar)
• Presents with severe trismus

6. Peritonsillar Space

• Lies between the fibrous tonsillar capsule and the superior pharyngeal constrictor muscle
• Contains loose areolar tissue
• Site of peritonsillar abscess (quinsy) - the most common deep neck infection in adults
• Infection can spread from here to the parapharyngeal space

7. Submandibular Space

• Bounded by the investing layer of deep cervical fascia (floor) and the mucosa of the floor of the mouth (roof)
• The mylohyoid muscle divides it into:
  • Sublingual space (above mylohyoid): contains sublingual gland, Wharton's duct, lingual nerve, hypoglossal nerve
  • Submandibular space proper (below mylohyoid): contains submandibular gland, lymph nodes, facial artery and vein
• Both sublingual and submandibular spaces communicate around the posterior free edge of the mylohyoid muscle
• Infection source: mandibular molars (particularly lower 2nd/3rd molars)

8. Parotid Space

• Formed by the investing layer of deep cervical fascia splitting to encompass the parotid gland
• Contains: parotid gland, facial nerve (CN VII), retromandibular vein, terminal branches of external carotid artery, parotid lymph nodes

INFRAHYOID / SPANNING SPACES

9. Carotid Space

• A potential space within the carotid sheath, formed from condensation of all three layers of deep cervical fascia
• Extends from the skull base to the thoracic inlet
• Contents: common carotid artery, internal jugular vein, vagus nerve (CN X)
• In the suprahyoid neck, also contains internal carotid artery and cranial nerves IX, XI, XII
• Lesions: carotid body tumour (paraganglioma), vagal schwannoma, IJV thrombosis (Lemierre syndrome), neuroblastoma in children

10. Visceral Space (Pretracheal Space)

• Bounded by the middle layer of deep cervical fascia
• Contains: larynx, hypopharynx, cervical esophagus, proximal trachea, thyroid, parathyroid glands, lymphatics of Level VI
• Extends from hyoid to mediastinum
• Infection can spread from thyroid abscess or tracheal/esophageal perforation

III. CLINICAL CORRELATIONS AND SPREAD OF INFECTION

Routes of Spread

Peritonsillar/Submandibular space
          ↓
Parapharyngeal space
          ↓
Retropharyngeal space
          ↓
Danger space (alar space)
          ↓
Posterior mediastinum → Descending necrotizing mediastinitis

Source of Deep Neck Infections

1. Odontogenic (most common - lower molar teeth) → submandibular/masticator space
2. Pharyngitis/tonsillitis → peritonsillar → parapharyngeal → retropharyngeal
3. Foreign body/instrumentation → retropharyngeal or prevertebral
4. Parotitis → parotid space
5. Cervical lymphadenitis → any neck space

IV. DIAGNOSIS AND INVESTIGATION

• CT with contrast: Investigation of choice for deep neck space infections; demonstrates rim-enhancing collections, airway deviation, and extent of spread; "bow-tie" appearance of alar space involvement on axial imaging
• MRI: Better soft tissue resolution; useful for delineating PPS tumours; T1WI shows fat in PPS as bright signal
• Clinical assessment: trismus (masticator), muffled voice/bulging posterior wall (retropharyngeal), unilateral tonsillar displacement (peritonsillar/parapharyngeal)

V. MANAGEMENT OF DEEP NECK SPACE INFECTIONS

Priorities: Airway - Antibiotics - Abscess drainage

• Early endotracheal intubation (awake flexible intubation if possible)
• Tracheostomy if:
  • Worsening stridor/dyspnea, <50% normal airway diameter
  • Anticipated prolonged (>48 h) airway edema
  • Not easily intubatable

• Broad-spectrum empiric therapy immediately (do not wait for cultures)
• First-line: Ampicillin-sulbactam 1.5-3 g IV every 6 hours
• Penicillin allergy: Clindamycin 600-900 mg IV every 8 hours
• Clindamycin is first-line in children <2 years (increasing MRSA rates)
• If Eikenella suspected (bite wounds): Moxifloxacin 400 mg IV/PO daily
• Hospital-acquired/MRSA: Add vancomycin

• Mandatory indications: Abscess >2.5 cm, multiple space involvement, descending infection, failed medical therapy, immunocompromised patient, airway compromise

VI. COMPLICATIONS OF DEEP NECK SPACE INFECTIONS

1. Airway obstruction (most immediate life threat)
2. Descending necrotizing mediastinitis (via danger space) - mortality 20-40%
3. Jugular vein thrombosis / Lemierre syndrome (carotid space involvement)
4. Carotid artery erosion / rupture - "herald bleed" preceding massive hemorrhage
5. Aspiration pneumonia
6. Septicemia and septic shock
7. Cranial nerve palsies (IX, X, XI, XII from carotid space involvement)
8. Horner's syndrome (sympathetic chain involvement in post-styloid PPS)

SUMMARY TABLE