Histology of Skin

Layers Overview

1. EPIDERMIS

Layers of the Epidermis (deep to superficial)

Stratum Basale (Stratum Germinativum)

• Basophilic cytoplasm (closely spaced nuclei impart a deep blue stain)
• Connected to each other and overlying spinous cells by desmosomes
• Attached to the basal lamina by hemidesmosomes
• Contains scattered melanin granules transferred from neighboring melanocytes
• New keratinocytes generated here migrate upward, beginning their terminal differentiation journey

Stratum Spinosum (Prickle Cell Layer)

• Cytoplasmic spines (processes) linked to adjacent cells by desmosomes - visible as the "node of Bizzozero" (slight thickenings at desmosomal sites)
• Called "prickle cells" because cells shrink during histological processing, leaving expanded intercellular spaces between the spines
• Keratin intermediate filaments (tonofibrils) assemble here and converge at desmosomes
• Cells become progressively more flattened toward the surface

Stratum Granulosum

1. Keratohyalin granules - basophilic, irregular granules containing loricrin and profilaggrin, which cross-link keratin filaments
2. Lamellar bodies (membrane-coating granules / Odland bodies) - secreted at the interface with stratum corneum to form the epidermal water barrier (lipid-rich secretion). The turnover time through stratum spinosum + granulosum is ~31 days.

Stratum Lucidum

Stratum Corneum

• Cells (corneocytes) lack nuclei and organelles
• Packed with keratin filaments within a cornified envelope
• Cells are eventually shed (desquamation) from the surface
• Average thickness: 16-20 cell layers; turnover ~14 days in this layer
• The total epidermal turnover time is ~15-30 days

Non-Keratinocyte Cells of the Epidermis

1. Keratinocytes (~80%)

2. Melanocytes

• Dendritic cells of neural crest origin, located mainly in the stratum basale (1 per 4-40 basal keratinocytes - constant ratio across all skin types)
• Produce melanin in lysosome-related organelles called melanosomes (derived from Golgi)
• Synthesis pathway: L-tyrosine → L-DOPA → L-DOPAquinone → eumelanin (black-brown, when cysteine insufficient) or pheomelanin (yellow-red, when cysteine abundant), via the enzyme tyrosinase
• Mature melanosomes (Stage IV) travel to the tips of dendritic processes and are transferred to adjacent keratinocytes by a process called pigment donation - keratinocytes phagocytose the tips of melanocyte processes
• Melanosomes accumulate above and around keratinocyte nuclei, forming a "melanosome microparasol" that shields nuclear DNA from UV radiation
• Skin color differences arise from the number, size, and distribution of melanosomes - not the number of melanocytes
• Regulated by MSH (via MC1R receptor), ACTH, sex steroids, and UV exposure

3. Langerhans Cells

• Dendritic antigen-presenting cells (resident macrophages) of the epidermis
• Derived from erythro-myeloid progenitor cells of the yolk sac - self-renewing, cannot be replenished by bone marrow monocytes
• Located primarily in the stratum spinosum
• In H&E sections appear as clear cells (like melanocytes, they do not pick up conventional stains well)
• Identified by CD1a, CD207 (langerin), and Birbeck granules (racket-shaped, visible only on electron microscopy - pathognomonic)
• Function: immunosurveillance - extend processes through tight junctions to sample the epidermal microenvironment; process antigens and migrate to lymph nodes as immunostimulatory cells
• Respond to pathogens and contact sensitizers (relevant in allergic contact dermatitis)

4. Merkel Cells

• Located in the stratum basale, especially in touch-sensitive areas (fingertips, lips)
• Modified epithelial cells acting as mechanoreceptors for light touch
• Contain dense-core granules with neuropeptides
• Associated with disc-shaped terminals of myelinated sensory (Type II) nerve fibers
• The Merkel corpuscle = Merkel cell + associated disc receptor
• Clinically relevant: Merkel cell carcinoma is an aggressive neuroendocrine skin tumor

2. DERMIS

Two Layers

Papillary Layer (superficial)

• Loose connective tissue immediately beneath the epidermis
• Thin collagen fibers: predominantly type I and type III collagen (ratio of type III:I increases with age)
• Thread-like elastic fibers forming an irregular network
• Contains dermal papillae and dermal ridges that interdigitate with the epidermis (increasing surface area of dermal-epidermal junction)
• Rich in blood vessels (capillary loops supplying but not entering the epidermis), lymphatics, and nerve processes
• Sensory nerve endings and receptors are concentrated here (Meissner corpuscles in dermal papillae)

Reticular Layer (deep)

• Always thicker and less cellular than the papillary layer
• Thick, irregular bundles of predominantly type I collagen and coarser elastic fibers
• Collagen = tensile strength; Elastic fibers = elasticity and resiliency
• Collagen/elastic bundles run in regular Langer's lines (cleavage lines) - surgical incisions parallel to these lines heal with minimal scarring
• Contains adnexal structures (hair follicles, sweat glands, sebaceous glands), smooth muscle (arrector pili), blood vessels, and nerves

Cells of the Dermis

• Fibroblasts - dominant structural cells; secrete collagen (types I, II, III, V, VII), proteoglycans, glycosaminoglycans, and multiadhesive glycoproteins; also have immune defense roles (express toll-like receptors)
• Dermal dendritic cells and resident macrophages (mononuclear phagocyte system)
• Mast cells - scattered throughout
• Lymphocytes - CD4+, CD8+, γ/δ T cells, regulatory T cells, NK cells, skin-resident memory T cells (Trm)
• Note: neutrophils are normally absent but infiltrate with injury or UV exposure

3. HYPODERMIS (Subcutaneous Layer)

• Equivalent to the subcutaneous fascia of gross anatomy
• Contains variable amounts of adipose tissue arranged in lobules separated by connective tissue septa
• Provides thermal insulation and energy reserve
• Contains the lower portions of hair follicles and sweat glands, larger blood vessels, and nerves
• The thin, largely vestigial panniculus carnosus (striated muscle) lies deep to the hypodermis; remnants persist as platysma and facial expression muscles in humans

4. SKIN APPENDAGES (Adnexal Structures)

5. SENSORY RECEPTORS OF THE SKIN

6. THICK SKIN vs. THIN SKIN

7. VASCULAR SUPPLY

Clinical Correlations

• Vitiligo: selective loss of melanocytes → depigmentation
• Albinism: normal melanocyte count but defective melanin synthesis pathway
• Psoriasis: keratinocyte hyperproliferation → loss of granular layer, parakeratosis
• Langerhans cell histiocytosis: clonal proliferation of Langerhans cells; diagnosed by Birbeck granules on EM or CD1a/CD207 on immunohistochemistry
• Merkel cell carcinoma: aggressive neuroendocrine tumour of skin
• Langer's lines: incisions parallel to these heal with minimal scarring - important in surgery
• Friction blisters: space formed between epidermis and dermis of thick skin; calluses represent protective hyperkeratosis

Note: "Renoria" appears to be a spelling variant or typo for rhinorrhea. This answer covers CSF rhinorrhea (cerebrospinal fluid leaking through the nose).

Cerebrospinal Fluid (CSF) Rhinorrhea

CSF Physiology (Background)

• CSF is produced by the choroid plexus in the ventricles at a rate of ~20 mL/hour in adults
• Total CSF volume = 140 mL: 20 mL in ventricles, 50 mL in intracranial subarachnoid space, 70 mL in paraspinal subarachnoid space
• Normal CSF pressure: 4 cm H₂O (infants) to 14 cm H₂O (adults)
• Pressure fluctuates with respiration, arterial pulsation, and head position
• CSF resorption by arachnoid villi plays the major role in maintaining ICP - disruption leads to elevated ICP

Classification (Ommaya et al.)

I. TRAUMATIC

1. Immediate (within 48 hrs)
2. Delayed (days to weeks after injury)

1. Neurosurgical procedures - transsphenoidal hypophysectomy, frontal craniotomy, other skull base procedures
2. Rhinologic procedures - endoscopic sinus surgery (ESS), septoplasty, combined skull base procedures

II. NONTRAUMATIC

• Hydrocephalus
• Intracranial masses
• Empty sella syndrome (ESS) - pulsatile CSF pressure transmitted through arachnoid herniation into sella

• Neoplasm (direct erosion of skull base)
• Infection (e.g., osteomyelitis)
• Granulomatous disease (granulomatosis with polyangiitis)

• Actually, most "idiopathic" cases have occult elevated ICP (mean 26-32 cm H₂O on lumbar puncture) - the CSF leak may serve as a pressure release valve

Epidemiology

• ~80% of CSF rhinorrhea results from accidental trauma (mostly closed head injury)
• CSF rhinorrhea occurs in only 2-3% of serious head trauma cases
• Skull base fracture is associated with a CSF fistula in 12-30% of cases
• More than 50% of traumatic CSF fistulas are at the anterior cranial base, mostly at the cribriform plate
• Only 4% of all CSF leaks are truly nontraumatic
• 16% result from intracranial/extracranial procedures
• Iatrogenic leaks are increasingly common: ~0.5% rate during endoscopic sinus surgery
• Most traumatic CSF leaks manifest within 2 days and almost all within 3 months of injury

Common Sites of Skull Base Defects

Clinical Features

Symptoms

• Watery, clear, unilateral nasal discharge - the hallmark; often described as salty tasting
• Volume increases with head-down position (Valsalva, straining, coughing, bending forward)
• Bilateral rhinorrhea suggests bilateral skull base defects
• Headache - positional, often relieved when lying flat (from intracranial hypotension when actively leaking)
• History of head trauma, prior skull base surgery, or trans-sphenoidal procedure is key

"Halo" or "Ring" Sign

• When CSF-containing nasal discharge drips onto a pillow or gauze, the CSF migrates further than blood/mucus, forming a pale outer ring around a darker central spot
• Not a specific test but raises suspicion

Diagnosis

1. Confirm the presence of CSF in the nasal secretion
2. Localize the skull base defect

Step 1 - Confirm CSF

Beta-2 Transferrin (β-2 transferrin)

• Gold standard chemical marker
• A isoform of transferrin found almost exclusively in CSF (also in perilymph and aqueous humor - not in nasal secretions, serum, or saliva)
• Highly specific and sensitive
• Method: fluid is collected, sent for protein electrophoresis
• Limitations: requires ~0.5 mL of fluid; result may take days

Beta-trace Protein (β-TP / prostaglandin D2 synthase)

• Another highly specific CSF marker
• Faster turnaround than β-2 transferrin
• Both tests have significantly replaced older, less specific cisternography tests

Glucose Testing

• A nasal secretion glucose >30 mg/dL suggests CSF, but this is non-specific (glucose is also elevated in hyperglycemia, secretory rhinitis) - not reliable

Intrathecal Fluorescein

• Fluorescein dye injected intrathecally (into CSF)
• Used intraoperatively (and sometimes preoperatively) for precise localization of the leak
• Nasal endoscopy reveals a greenish hue at the defect site
• Confirms active leak and guides repair
• Not FDA-approved for intrathecal use but widely employed off-label

Step 2 - Localize the Defect

High-Resolution CT (HRCT) of the Skull Base

• First-line imaging after chemical confirmation
• 1 mm direct coronal images (or reformatted from 1 mm axial data)
• Identifies bony skull base dehiscences, fracture lines
• Provides excellent bony anatomical detail
• A bony defect on CT alone (without positive β-2 transferrin) is insufficient to diagnose active CSF leak

MRI of the Skull Base

• Complementary to CT
• Superior soft tissue detail
• Identifies meningoceles and meningoencephaloceles herniating through defects
• Detects empty sella (suggesting elevated ICP as etiology)
• MR with gadolinium or MR angiography helps identify vessels within encephaloceles (to avoid stroke during repair)

CT/MR Fusion

• Hybrid technique combining CT bony detail with MR soft tissue signal
• Emerging tool for complex defects

Cisternography (Radionuclide or CT)

• Now relegated to selected cases only due to high specificity of β-2 transferrin and β-TP
• CT cisternography: intrathecal iodinated contrast + CT; useful for large defects or when multiple potential sites are present

Management

Conservative (Non-Surgical)

• Bed rest with head of bed elevation (30°)
• Avoidance of nose-blowing, Valsalva, straining
• Lumbar drainage (CSF diversion) - reduces ICP and flow through the defect
• Most traumatic leaks resolve spontaneously within 1 week with conservative measures
• Prolonged CSF leak > 7-10 days increases meningitis risk - earlier surgical intervention warranted

Surgical Management

• All spontaneous/idiopathic leaks (will not resolve without repair)
• All iatrogenic leaks
• Traumatic leaks that fail conservative management (>7-10 days)
• Leaks with pneumocephalus
• Prevention of ascending meningitis

Endoscopic Repair (Primary Surgical Approach)

1. Standard endoscopic dissection for exposure of defect
2. Intrathecal fluorescein administered to identify the defect
3. Preparation of defect margins: mucosa within 5 mm of the defect removed (to allow graft adherence)
4. Fulguration of any herniated meningocele/meningoencephalocele (never push it intracranially - risk of CSF gush and pneumocephalus)
5. Graft placement

• Temporalis fascia, fascia lata
• Pedicled middle turbinate flaps
• Free cartilage/bone grafts (nasal septum, calvarium)
• Autogenous fat ("bath-plug" technique for small defects)
• Acellular dermal allograft
• Xenogeneic collagen dural substitutes (Durepair, Dura-Gen) for larger defects
• Meta-analysis (Hegazy et al., 289 fistulae): graft material choice does not significantly alter outcome

• Underlay technique: graft placed on the intracranial side of the defect - ambient ICP holds it in place
• Bath-plug technique (Wormald): intracranial fat graft anchored by ICP
• Free grafts generally preferred over pedicled grafts (lower failure rate)

Intracranial (Open) Repair

• Reserved for complex, large, or posterior defects not accessible endoscopically
• Involves frontal craniotomy with direct dural repair
• Higher morbidity; anosmia risk (if cribriform plate dissected)
• Transglabellar subcranial approach allows direct access to anterior fossa floor with less frontal lobe retraction

Management of Elevated ICP

• All nontraumatic/idiopathic CSF rhinorrhea should be evaluated for occult raised ICP (even after successful repair)
• Lumbar puncture opening pressure measurement is essential post-repair
• If elevated ICP confirmed: treat with acetazolamide, weight loss (if obese), or CSF diversion (ventriculoperitoneal shunt, lumboperitoneal shunt)
• Failure to address elevated ICP leads to recurrence of the CSF leak after repair

Complications of Untreated CSF Rhinorrhea

Antibiotic Prophylaxis

Hiatus Semilunaris

Definition

Location

Boundaries

• Medially: opens into the middle meatus
• Laterally: opens into the ethmoidal infundibulum (a 3D funnel-shaped space)

Relationship to the Ethmoidal Infundibulum

Endoscopic and CT Anatomy

Structures that Drain through / near the Hiatus Semilunaris

The Osteomeatal Complex (OMC)

1. Maxillary ostium - main drainage channel of maxillary sinus
2. Ethmoidal infundibulum - 3D corridor draining maxillary and anterior ethmoid sinuses
3. Hiatus semilunaris - the 2D slit connecting infundibulum to middle meatus
4. Uncinate process - sickle-shaped bone forming the anterior border of the hiatus
5. Bulla ethmoidalis - the largest anterior ethmoid air cell, forming the posterior border
6. Anterior ethmoid cells
7. Ostia of frontal, maxillary, and anterior ethmoid sinuses

The OMC is bounded laterally by the lamina papyracea and medially by the middle turbinate; superiorly by the fovea ethmoidalis; posteriorly by the basal lamella of the middle turbinate.

The Uncinate Process - Key Relationship

Embryological Origin

• The descending aspect of the first furrow forms the ethmoidal infundibulum, hiatus semilunaris, and middle meatus
• The maxillary sinus develops from the inferior aspect of the infundibulum

Clinical Significance

1. Chronic Rhinosinusitis (CRS)

• Mucosal inflammation → edema of uncinate/bulla → narrowing of hiatus → obstructed drainage
• Retained secretions → reduced aeration → mucosal hypoxia → ciliary dysfunction → mucus stasis → secondary infection → perpetuating cycle

2. Functional Endoscopic Sinus Surgery (FESS)

• Uncinectomy (removal of uncinate process) opens the hiatus and exposes the infundibulum
• This provides access to the maxillary sinus ostium, anterior ethmoid cells, and frontal recess
• Middle meatal antrostomy (widening of maxillary ostium) is performed after entering through the infundibulum

1. Uncinectomy → opens hiatus semilunaris
2. Anterior ethmoidectomy (bulla removal)
3. Posterior ethmoidectomy
4. Sphenoidotomy / frontal sinusotomy as required

3. Nasal Polyps

4. Accessory Maxillary Ostia (Nasal Fontanelles)

5. Imaging

• Look for infundibular width, uncinate position, and air-filled ethmoidal infundibulum
• Opacification of the infundibulum/hiatus region on CT is the hallmark of OMC obstruction
• OMC disease is a contraindication to non-surgical management in recurrent CRS

Summary Table

External Carotid Artery and Its Branches

Overview

Origin and Course

• Arises from the common carotid artery at the carotid bifurcation at the superior margin of the thyroid cartilage
• Initially lies anteromedial to the internal carotid artery; higher up it lies anterolateral to it
• Exits the carotid sheath and travels upward between the superior border of the thyroid cartilage and the neck of the mandible
• In the carotid triangle, it is crossed by the hypoglossal nerve (CN XII) and the facial and lingual veins
• Superior to the carotid triangle, it is crossed by the posterior belly of digastric and stylohyoid muscles
• Within the parotid gland, it is crossed by the facial nerve (CN VII)
• Divides into its two terminal branches (superficial temporal + maxillary arteries) at the neck of the mandible within the parotid gland

The Eight Branches - Grouped

Mnemonic: "Some Anatomists Like Freaking Out Poor Medical Students" = Superior thyroid, Ascending pharyngeal, Lingual, Facial, Occipital, Posterior auricular, Maxillary, Superficial temporal

Detailed Branches

ANTERIOR BRANCHES

1. Superior Thyroid Artery

• First and most inferior branch of the ECA (occasionally arises from the common carotid - an important anatomical variant)
• Origin: at or just below the level of the superior margin of the thyroid cartilage, close to the bifurcation
• Course: runs anteroinferiorly, deep to the infrahyoid muscles, to the superior pole of the thyroid gland
• The external branch of the superior laryngeal nerve runs in close proximity - at risk during thyroid surgery

• Infrahyoid artery - along the lower border of the hyoid
• Superior laryngeal artery - pierces the thyrohyoid membrane with the internal laryngeal nerve; supplies the interior of the larynx
• Sternocleidomastoid branch
• Cricothyroid artery - supplies cricothyroid muscle; anastomoses across the midline (clinically relevant in emergency cricothyrotomy)
• Glandular branches to the superior pole of the thyroid

2. Lingual Artery

• Second anterior branch
• Origin: from the anterior surface of the ECA at the level of the tip of the greater horn of the hyoid bone, just above the superior thyroid artery
• Course: loops superoanteriorly on the middle constrictor, runs deep to the hypoglossal nerve (CN XII), stylohyoid, and posterior belly of digastric; then passes deep to the hyoglossus muscle to reach the sublingual region and tongue
• The Pirogoff's triangle (or lingual triangle) - bounded by the hyoglossus, posterior belly of digastric, and hypoglossal nerve - is the surgical landmark for locating the lingual artery in the neck

• Suprahyoid artery - along upper border of hyoid
• Dorsal lingual branches - to dorsum of tongue and tonsil
• Sublingual artery - to sublingual gland and floor of mouth
• Deep lingual artery - terminal branch; runs to tip of tongue on its inferior surface

3. Facial Artery

• Third anterior branch (arises just above the lingual artery - may share a common trunk with it: "linguofacial trunk")
• Origin: in the carotid triangle, just above the lingual artery
• Cervical course: passes deep to the stylohyoid and posterior belly of digastric, then deep between the submandibular gland and mandible, loops through a groove on the posterior surface of the submandibular gland
• Enters the face by hooking over the inferior border of the mandible just anterior to the masseter muscle (palpable pulse point)
• Facial course: ascends tortuously toward the medial angle (canthus) of the eye as the angular artery

• Ascending palatine artery
• Tonsillar artery (major blood supply to palatine tonsil)
• Glandular branches to submandibular gland
• Submental artery

• Inferior labial artery
• Superior labial artery (gives off septal branches to nasal septum/Kiesselbach's area)
• Lateral nasal artery
• Angular artery (terminal branch) - anastomoses with the ophthalmic artery (a branch of the internal carotid) at the medial canthus

POSTERIOR BRANCHES

4. Occipital Artery

• Origin: from the posterior surface of the ECA, near the level of origin of the facial artery
• Course: passes superoposteriorly, deep to the posterior belly of digastric (a key surgical landmark - the occipital artery is a guide to the posterior belly); crosses the internal carotid artery, glossopharyngeal, vagus, and spinal accessory nerves, and deep cervical muscles
• Emerges on the posterior scalp by piercing the attachment of trapezius/sternocleidomastoid to the occipital bone
• Terminal branches: medial and lateral branches to the posterior scalp

• Sternocleidomastoid branches (2)
• Auricular branch
• Mastoid branch - enters skull via mastoid foramen; supplies mastoid cells and meninges
• Descending branches - to deep muscles of the neck and back
• Meningeal branch - to posterior cranial fossa
• Terminal scalp branches

5. Posterior Auricular Artery

• Small branch from the posterior surface of the ECA
• Origin: at the level of the superior border of the posterior belly of digastric; arises just above the digastric/stylohyoid
• Course: passes superiorly between the external acoustic meatus and mastoid process

• Stylomastoid artery - enters the stylomastoid foramen; supplies the facial nerve canal, middle ear, mastoid air cells
• Auricular branch - to the posterior surface of the auricle (pinna)
• Occipital branch - to the scalp posterior to the ear

MEDIAL BRANCH

6. Ascending Pharyngeal Artery

• The smallest and most medial branch; often the second branch given off (between the superior thyroid and lingual)
• Origin: from the posterior (medial) surface of the ECA, just above the superior thyroid artery
• Course: a long, narrow vessel that ascends along the lateral wall of the pharynx, medial to the internal carotid artery, to the base of the skull

• Pharyngeal branches (3-4) - to pharyngeal constrictors, stylopharyngeus, soft palate
• Prevertebral branches - to prevertebral muscles
• Inferior tympanic artery - enters the tympanic canaliculus; supplies the middle ear (anastomoses with other tympanic branches)
• Posterior meningeal branches - pass through jugular foramen and hypoglossal canal to supply meninges of the posterior cranial fossa

TERMINAL BRANCHES

7. Superficial Temporal Artery

• One of the two terminal branches of the ECA; appears as a direct upward continuation
• Origin: behind the neck of the mandible within the parotid gland
• Course: emerges from the superior border of the parotid gland, passes anterior to the ear, crosses the zygomatic process of the temporal bone (palpable as a pulse just in front of the tragus)
• Divides above the zygomatic arch into anterior (frontal) and posterior (parietal) branches
• Gives off the transverse facial artery as it exits the parotid gland

• Transverse facial artery - runs horizontally across the face between the parotid duct and zygomatic arch; supplies the parotid, masseter, and overlying facial skin
• Anterior auricular branches - to the auricle and external acoustic meatus
• Middle temporal artery - pierces the temporal fascia; supplies the temporalis muscle
• Zygomatico-orbital artery - to the orbicularis oculi
• Frontal (anterior) branch - to the forehead and scalp
• Parietal (posterior) branch - to the temporal and parietal scalp regions

Clinical note: The superficial temporal artery is the site most often used for temporal artery biopsy in suspected giant cell (temporal) arteritis. It is also used for scalp flaps and free flap anastomosis in reconstructive surgery.

8. Maxillary Artery

• The larger of the two terminal branches of the ECA
• Origin: posterior to the neck of the mandible, within the parotid gland
• Course: passes horizontally and deep to the neck of the mandible (or sometimes superficial to the lateral pterygoid), through the infratemporal fossa, and continues through the pterygomaxillary fissure into the pterygopalatine fossa
• Divided into three parts by the lateral pterygoid muscle:

• Middle meningeal artery - enters skull via foramen spinosum; supplies dura (main supply) - torn in extradural haematoma
• Accessory meningeal artery - via foramen ovale
• Deep auricular artery - to external acoustic meatus and lateral surface of tympanic membrane
• Anterior tympanic artery - to medial surface of tympanic membrane
• Inferior alveolar artery - enters mandibular foramen; gives off mental branch (exits mental foramen); supplies mandibular teeth, chin skin

• Masseteric artery
• Pterygoid branches (medial and lateral)
• Deep temporal arteries (anterior and posterior) - to temporalis
• Buccal artery - to buccinator and buccal mucosa

• Posterior superior alveolar artery - to upper molar teeth and maxillary sinus
• Infraorbital artery - enters orbit via inferior orbital fissure; exits via infraorbital foramen; supplies infraorbital skin, lower eyelid, upper lip, and upper incisor/canine teeth
• Greater palatine artery - descends via greater palatine foramen; supplies hard palate
• Lesser palatine arteries - via lesser palatine foramina; to soft palate and tonsil
• Pharyngeal artery - to roof of pharynx and sphenoidal sinus
• Sphenopalatine artery (the largest terminal branch) - enters nasal cavity via the sphenopalatine foramen; the main blood supply to the nasal cavity; supplies nasal lateral wall and septum; a major source of posterior epistaxis - can be catheterized from the femoral route for embolization

Relationships of the ECA - Surgical Importance

Distinguishing ECA from Internal Carotid Artery

Anatomical Variants (Clinically Important)

• Superior thyroid artery may arise from the common carotid artery
• Lingual and facial arteries may arise from a common trunk (linguofacial trunk) - present in ~20%
• Posterior auricular artery may arise from the occipital artery
• Ascending pharyngeal artery may originate more superiorly than usual
• Middle meningeal artery occasionally arises from the ophthalmic artery (branch of internal carotid)

Summary Table

Cavernous Sinus

Definition

Location and Extent

• Lies in the middle cranial fossa, on either side of the body and greater wing of the sphenoid bone
• Extends from the apex of the orbit anteriorly to the apex of the petrous temporal bone posteriorly
• Medial wall is grooved into the body of the sphenoid (housing the sella and pituitary gland)
• Inferior wall grooves the base of the greater wing of the sphenoid
• The medial, upper, and lateral walls are formed by a fold of the inner layer of dura mater, which is medially continuous with the diaphragma sellae
• Posterolaterally, the wall is medial to the anterior part of Meckel's cave (which contains the trigeminal ganglion)

Contents

Within the Lateral Wall (from superior to inferior):

1. Oculomotor nerve (CN III) - most superior, in the upper lateral wall
2. Trochlear nerve (CN IV) - below CN III in the lateral wall
3. Ophthalmic nerve (V₁) - below CN IV
4. Maxillary nerve (V₂) - lowest in the lateral wall

Within the Sinus Itself (free in the venous blood):

1. Internal carotid artery (ICA) - runs an S-shaped course (the "carotid siphon") through the sinus
2. Abducens nerve (CN VI) - runs within the sinus (not in the lateral wall), directly lateral to the ICA - therefore most susceptible to raised ICP and most commonly affected in cavernous sinus pathology

Key memory aid: "O TOM CAT" - Oculomotor, Trochlear, Ophthalmic, Maxillary in the wall; Carotid Artery (and abducens nerve) Traversing the interior. Or: the structures in the lateral wall (III, IV, V1, V2) are embedded in dura and relatively protected; the ICA and CN VI are free in the venous blood and maximally exposed.

Also within or passing through:

• Sympathetic plexus around the ICA (postganglionic sympathetic fibers from the superior cervical ganglion)
• Branches of the meningohypophyseal trunk (first branch of the cavernous ICA)

Walls and Bony Relations

Arterial Relations

• Meningohypophyseal trunk - supplies meninges, posterior pituitary, and tentorium
• Inferolateral trunk - supplies cranial nerves within the sinus

Venous Connections (Tributaries and Drainage)

Tributaries (Inflow):

Drainage (Outflow):

Important: Cerebral veins and venous sinuses have no valves - blood can flow in either direction. This bidirectional flow allows facial/sinus infections to spread retrogradely into the cavernous sinus.

Routes of Infection to the Cavernous Sinus

1. Facial/orbital route: Facial/periorbital infection → angular vein → superior ophthalmic vein → cavernous sinus (the "danger area of the face" - central face, upper lip, nose)
2. Sinonasal route: Sphenoid or ethmoid sinusitis → small emissary veins → cavernous sinus (most common cause of septic CST)
3. Pterygoid plexus route: Dental infection / infratemporal fossa → pterygoid plexus → via foramen ovale to cavernous sinus

Cavernous Sinus Syndrome

Clinical Features

Key distinguishing feature: CN VI (abducens) palsy is often the earliest and most common finding because the abducens nerve runs free within the sinus (not in the protected lateral wall), making it the most vulnerable nerve.

CN V3 (mandibular) is not involved in cavernous sinus syndrome because V3 exits the skull via foramen ovale and does not pass through the cavernous sinus.

Causes of Cavernous Sinus Syndrome

Septic / Infectious

• Cavernous sinus thrombosis (CST) - bacterial: sphenoid/ethmoid sinusitis, dental abscess, facial cellulitis; fungal: mucormycosis (angioinvasive, particularly in diabetics/immunocompromised)
• Herpes zoster

Vascular

• Carotid-cavernous fistula (CCF) - direct (traumatic, high-flow) or indirect (dural, spontaneous)
• Internal carotid artery aneurysm
• ICA dissection, dolichoectasia
• Superior ophthalmic vein thrombosis

Neoplastic

• Pituitary adenoma (with lateral extension)
• Meningioma
• Nasopharyngeal carcinoma (direct extension)
• Lymphoma, plasmacytoma
• Skull base metastases
• Sphenoid sinus tumours

Inflammatory

• Tolosa-Hunt syndrome - painful idiopathic granulomatous inflammation; responds to corticosteroids; diagnosis of exclusion
• Granulomatosis with polyangiitis (Wegener's)
• Sarcoidosis

Other

• Pituitary apoplexy (sudden haemorrhage into pituitary tumour → bilateral CN palsies + visual loss)

Cavernous Sinus Thrombosis (CST)

Septic CST

• Most common sources: sphenoid and ethmoid sinusitis
• Also: orbital cellulitis, facial/dental infections
• Organisms: Staphylococcus aureus (most common), Streptococci, Gram-negatives, anaerobes; mucormycosis in immunocompromised

• Fever (often high, spiking), severe headache
• Frontal and retroorbital pain
• Diplopia (early - CN VI palsy commonest)
• Ptosis, proptosis, chemosis
• Extraocular dysmotility (CN III, IV, VI)
• Hyperesthesia of V1 and V2; decreased corneal reflex
• Dilated, tortuous retinal veins; papilledema
• If bilateral → bilateral proptosis/ophthalmoplegia (pathognomonic for CST)
• May progress to meningitis, brain abscess, septicaemia

Aseptic (Non-infectious) CST

• Hypercoagulable states (antiphospholipid antibodies, malignancy, pregnancy, OCP)
• Dehydration
• Inflammatory conditions

Diagnosis

• MRI brain with gadolinium + MR venography (MRV) - absent flow void in the cavernous sinus; enhancement of sinus walls
• CT venography - filling defect; also shows paranasal sinus disease
• Cerebral angiography (venous phase) - definitive but invasive

Treatment

1. IV antibiotics (6 weeks minimum) - directed at causative organism; empirically: broad-spectrum including MRSA cover
2. Drainage of source of infection (e.g., sphenoidectomy for sphenoid sinusitis)
3. Anticoagulation - heparin (controversial in septic CST but recommended for progressive neurological deterioration or aseptic CST)
4. For mucormycosis: amphotericin B + surgical debridement
5. Corticosteroids for Tolosa-Hunt syndrome

Carotid-Cavernous Fistula (CCF)

Summary of Contents (Memory Aid)

LATERAL WALL (superior → inferior):    |   WITHIN SINUS:
────────────────────────────────────   |   ──────────────
CN III  (Oculomotor)                   |   Internal Carotid Artery (ICA)
CN IV   (Trochlear)                    |   CN VI (Abducens) - lateral to ICA
CN V1   (Ophthalmic)                   |   Sympathetic plexus (on ICA)
CN V2   (Maxillary)                    |

CN V3 (Mandibular) does NOT pass through the cavernous sinus - it exits through foramen ovale directly.

Middle Meningeal Artery

Definition

Origin

• Branch of the maxillary artery (first part / mandibular part), given off in the infratemporal fossa
• The maxillary artery is itself a terminal branch of the external carotid artery
• MMA is thus ultimately a branch of: External carotid → Maxillary → Middle meningeal artery

Variant: The MMA occasionally arises from the ophthalmic artery (a branch of the internal carotid artery) rather than the maxillary artery.

Course

Step-by-step course:

1. Infratemporal fossa: Arises from the first part of the maxillary artery, in the infratemporal fossa deep to the lateral pterygoid muscle
2. Foramen spinosum: Enters the middle cranial fossa through the foramen spinosum (in the greater wing of the sphenoid) - the only artery to enter through this foramen
3. Extradural space: Runs in the outer (periosteal/endosteal) layer of the dura mater, tightly adherent to the inner surface of the skull in the middle cranial fossa
4. Division: Divides into anterior (frontal) and posterior (parietal) branches at a variable point

Branches

1. Anterior (Frontal) Branch

• The larger and more important branch clinically
• Passes almost vertically upward toward the vertex of the skull
• Crosses the pterion during its course - the thinnest part of the skull (H-shaped junction of the frontal, parietal, temporal, and greater wing of sphenoid)
• Lies in a groove on the inner surface of the temporal/parietal bone - often runs in a bony canal in adults (especially after age 40), making it more vulnerable to tearing with skull fracture
• Supplies the dura of the anterior and lateral parts of the middle cranial fossa and the inferolateral convexity

2. Posterior (Parietal) Branch

• Passes posterosuperiorly toward the parietal and occipital regions
• Supplies the dura of the posterior part of the middle cranial fossa

Other branches from the MMA within the skull:

• Superior tympanic artery - to the tensor tympani muscle and mucosa of the tympanic cavity
• Orbital branch - passes through the superior orbital fissure (or a small canal) to supply the dura of the anterior cranial fossa and anastomose with the lacrimal artery
• Petrosal branch - travels with the greater petrosal nerve through the hiatus of the facial nerve canal; supplies the tegmen tympani and geniculate ganglion
• Temporal branches - to the overlying temporalis muscle (after piercing the dura)

Surface Marking / Position of the Anterior Branch

• Midway between the superior margin of the orbit and the upper part of the external ear
• At the pterion - a small circular area in the temporal fossa where the sphenoid, frontal, parietal, and temporal bones of the skull come together
• This corresponds roughly to 2.5 cm above the midpoint of the zygomatic arch and 4 cm posterior to the frontozygomatic suture

The Pterion - Key Concept

Supply

• It supplies the dura mater, periosteum of the inner skull, and the bone itself (diploic supply)
• It does not primarily supply the brain parenchyma - the brain is supplied by the internal carotid and vertebral arterial systems

Comparison of Meningeal Arteries

Clinical Significance: Extradural (Epidural) Haematoma

Mechanism

• A lateral blow to the temporal/pterion region fractures the thin inner table of the squamous temporal bone
• This tears the anterior branch of the MMA (most commonly) running in the outer dural layer
• Blood escapes under pulsatile arterial pressure and gradually strips the dura away from the bone, forming an expanding extradural haematoma
• The process is progressive because: (a) the source is arterial and high-pressure; (b) the dura initially resists stripping, requiring time and pressure to accumulate

Classic Clinical Presentation ("Talk and Die")

1. Initial loss of consciousness - from the primary brain injury (concussion)
2. Lucid interval - patient recovers and appears neurologically normal; headache may be present
3. Rapid deterioration - as haematoma expands and ICP rises beyond compensatory capacity:
   • Severe headache
   • Vomiting
   • Decreasing conscious level
   • Contralateral hemiparesis (corticospinal tract compression)
   • Ipsilateral fixed dilated pupil (CN III compression from uncal herniation - Hutchinson pupil)
   • Bradycardia + hypertension + irregular breathing (Cushing's response = late sign of severe ICP)

This "talk and die" pattern occurs in only one-third of cases. Many patients never have a clear lucid interval, and EDH can also occur with prolonged primary loss of consciousness.

CT Appearance

• Biconvex (lenticular/lens-shaped) hyperdense collection between skull and brain
• Constrained by the dural attachment to suture lines (dura firmly adheres at sutures - the haematoma cannot cross sutures)
• Mass effect: midline shift, brain compression
• Associated skull fracture usually visible on bone windows
• Areas of mixed density within the haematoma indicate active/ongoing bleeding

Management

• Urgent neurosurgical evacuation (craniotomy/burr hole) for deteriorating/comatose patients or large haematomas
• Prognosis is excellent if evacuated promptly before herniation occurs
• Close observation with serial imaging for small haematomas in neurologically intact patients

Persistent Stapedial Artery - Important Variant

• The foramen spinosum is typically absent (a useful radiological sign)
• The MMA instead arises from the internal carotid artery via the persistent stapedial artery
• Clinically important in middle ear surgery (risk of massive haemorrhage) and skull base surgery
• PSA appears as an anomalous vessel on the promontory in the middle ear

Summary

Lingual Artery and Its Branches

Overview

Origin

• Arises from the anterior surface of the external carotid artery, just above the superior thyroid artery
• Origin is at the level of the tip of the greater horn (cornu) of the hyoid bone (C3 vertebral level)
• May share a common trunk with the facial artery (linguofacial trunk) in ~20% of cases - an important surgical variant

Course

Segment 1: Original (Root) Segment

• Arises from the ECA and forms a characteristic upward loop (the "lingual loop") then turns downward and forward
• Lies consistently 3-4 mm superolateral to the greater horn of the hyoid bone
• Encountered when skeletonizing the greater horn of the hyoid deep to the hyoglossus muscle during neck dissection

Segment 2: Within the Hyoglossus

• Passes deep to (beneath) the hyoglossus muscle - this is the KEY anatomical relationship
• Passes obliquely from posterosuperior to anteroinferior under the posterior border of hyoglossus
• Lies medial to the hypoglossal nerve (CN XII) - the hypoglossal nerve and lingual vein run on the outer (lateral/superficial) surface of hyoglossus, while the lingual artery runs on its deep surface
• Also runs deep to the stylohyoid muscle and posterior belly of digastric
• Passes between the middle constrictor of the pharynx and hyoglossus to enter the floor of the oral cavity via the oropharyngeal triangle (bounded by mylohyoid, superior constrictor, and middle constrictor)

Segment 3: Ascending Segment

• Ascends in a tortuous manner along the anterior border of hyoglossus
• The sublingual artery arises here (~0.8 cm above the hyoid bone)

Segment 4: Horizontal Segment (Deep Lingual Artery)

• Continues forward between hyoglossus and genioglossus muscles toward the apex of the tongue
• Runs with many upward and downward tortuosities between the longitudinal tongue muscles
• Becomes the deep lingual artery as the terminal segment

Key Relationship: The Hyoglossus Muscle

This relationship is critical in surgery: to find and ligate the lingual artery, the surgeon must go deep to the hyoglossus muscle. The hypoglossal nerve on the surface serves as a guide.

Branches

1. Suprahyoid Branch

• Arises from the initial (root) segment
• Small branch running along the upper border of the hyoid bone
• Anastomoses with the contralateral suprahyoid branch
• Supplies hyoid bone, suprahyoid muscles

2. Dorsal Lingual Arteries (Rami dorsales linguae)

• Usually 2-3 small branches
• Arise medial to the hyoglossus muscle (from the segment within hyoglossus)
• First branch of the lingual artery arises ~0.7 cm from the anterior border of hyoglossus
• Ascend to the posterior part of the dorsum of the tongue
• Vascular territory: root of tongue (5 mm behind the terminal sulcus), glossoepiglottic folds, palatoglossal arch (anterior pillar of fauces), soft palate, palatine tonsil, and epiglottis
• In the region of the valleculae, anastomose with epiglottic branches of the superior laryngeal artery

3. Sublingual Artery (Arteria sublingualis)

• Arises from the ascending segment at the anterior margin of hyoglossus (~0.8 cm above the hyoid bone)
• Passes forward between the genioglossus and mylohyoid muscles to reach the sublingual gland
• Vascular territory:
  • Ventral (undersurface) of the tongue
  • Anterior and lateral floor of the mouth
  • Vestibular and lingual gum (gingiva)
  • Sublingual gland
  • Overlying oral mucosa
• One branch enters the lingual foramen - a small opening on the posterior aspect of the mandibular symphysis immediately above the genial tubercles - to supply the anterior mandible and lower incisors (clinically relevant in implant surgery)
• Anastomoses with its contralateral fellow and with the submental artery (branch of facial artery)

4. Deep Lingual Artery (Arteria profunda linguae / Ranine artery)

• The terminal branch of the lingual artery
• The horizontal segment of the course
• Runs forward with many tortuosities in the plane between hyoglossus and genioglossus, then between the inferior longitudinal muscle and genioglossus
• Reaches the apex (tip) of the tongue on its inferior surface, near the lingual frenulum
• Visible through the thin mucosa of the undersurface of the tongue as the ranine veins are also visible alongside it
• At the tip, anastomoses with the contralateral deep lingual artery
• Supplies the intrinsic muscles and mucosa of the body and tip of the tongue

Summary of Branches

Important Relations - Summary

The Pirogoff (Lingual) Triangle

• Control of haemorrhage from tongue tumours
• Tongue base surgery
• Preparation before partial/total glossectomy

Venous Drainage (Companion Veins)

• Deep lingual vein: runs alongside the deep lingual artery anteriorly in the tongue; posteriorly separates from the artery and travels on the superficial (lateral) surface of hyoglossus alongside CN XII → drains to internal jugular vein
• Dorsal lingual vein: follows the lingual artery between hyoglossus and genioglossus → internal jugular vein
• The deep lingual veins are visible through the thin mucosa of the undersurface of the tongue as ranine veins

Nerve Relations (Clinically Important)

Clinical Significance

1. Tongue Cancer Surgery

• Before partial/total glossectomy, the lingual artery is ligated in the neck (at the Pirogoff triangle) to reduce intraoperative bleeding
• Langenbeck (1819) first described ligation of the lingual artery before tongue surgery

2. Haemorrhage Control

• Posterior tongue bleeding (from the dorsal lingual artery territory) can be life-threatening
• The dorsal lingual artery is the principal vessel encountered during transoral tongue base surgery (e.g., for obstructive sleep apnoea, tongue base tumours)
• Endovascular embolisation of the lingual artery is used for uncontrolled tongue haemorrhage

3. Neck Dissection

• The lingual artery is identified at the Pirogoff triangle and must be preserved or controlled during neck dissections
• The greater horn of the hyoid is used as a surgical landmark: the lingual artery lies 3-4 mm superolateral to it

4. Dental / Implant Surgery

• The sublingual artery sends a branch through the lingual foramen of the mandible
• During anterior mandibular implant placement, this branch can be injured, causing floor-of-mouth haematoma → airway compromise (life-threatening)

5. Anastomoses

• The lingual arteries are not end-arteries - they anastomose with contralateral fellow vessels at the tongue tip (deep lingual arteries) and at the hyoid (suprahyoid branches)
• This means bilateral ligation is required to fully devascularise the tongue