---

Nasal Septum and Little's Area

1. Overview and Functions

• Separating the two nasal airways
• Providing support to the nasal dorsum
• Maintaining the shape of the columella and nasal tip
• Forming part of the nasal valves (internal and external)
• Supporting humidification and filtration of inspired air

---

2. Structural Components

A. Bony Portion

• The perpendicular plate articulates: superiorly with the cribriform plate, posteriorly with the sphenoid crest, posteroinferiorly with the vomer, and anteroinferiorly with the septal cartilage.
• The posterior free edge of the vomer forms the posterior free edge of the septum.

B. Cartilaginous Portion

• Formed by the quadrilateral (septal) cartilage, a large four-sided hyaline cartilage
• Bound to the nasal bones, perpendicular plate of ethmoid, and vomer by collagenous fibers
• Continuous with the upper lateral cartilages at the bridge of the nose (forming the internal nasal valve at this junction)
• Posterior projection = the septal tail (sphenoidal process), which extends between the vomer and perpendicular plate - useful as a cartilage harvest site in revision rhinoplasty
• Inferior attachment to the maxillary nasal crest is via loose connective tissue, forming a pseudarthrosis that allows mobility and reduces fracture risk from trauma

C. Membranous Septum

• A small segment of connective tissue between the caudal edge of septal cartilage and the columella
• No skeletal component

---

3. Nasal Septal Swell Body

---

4. Blood Supply of the Nasal Septum

From the External Carotid Artery (via Internal Maxillary Artery):

From the Internal Carotid Artery (via Ophthalmic Artery):

Venous Drainage:

• Posteriorly via sphenopalatine vein into the pterygoid plexus
• Anteriorly into the facial veins
• Superiorly via ethmoidal veins into the superior ophthalmic system - with possible direct intracranial connections through the foramen caecum into the superior sagittal sinus (this creates a pathway for intracranial spread of infection)
• This is a valveless venous system, making retrograde spread of infection to the cavernous sinus possible. - KJ Lee's Essential Otolaryngology, p. 518

---

5. Nerve Supply

Sensory (Trigeminal Nerve):

Autonomic:

• Parasympathetic: Preganglionic fibers travel with the facial nerve → greater superficial petrosal nerve → joins deep petrosal nerve → forms the vidian nerve → synapse in the sphenopalatine ganglion → postganglionic fibers innervate nasal mucosa (controls secretion and vascular tone)
• Sympathetic: Postsynaptic fibers pass through the sphenopalatine ganglion and terminate in nasal mucosa (vasoconstriction, reduces secretion)
• The trigeminal fibers transmit pain, temperature, and touch from the nasal mucosa. - Cummings Otolaryngology, p. 566

---

6. Little's Area (Kiesselbach's Plexus)

Definition and Location

Arterial Contributions (5 vessels converge here):

Why Is It So Prone to Bleeding?

1. The vessels form a rich vascular bed of long capillary loops right beneath a thin, exposed mucosa
2. Located at the anterior septum where it is easily traumatized by digital trauma (nose picking) - the single most common cause
3. Exposed to turbulent, drying airflow at the nasal entrance, which can desiccate and crack the mucosa
4. Receives convergent blood supply from both carotid systems with no redundancy in pressure equalization

---

7. Nasal Lateral Wall and Nasal Cavity Reference

---

8. Clinical Relevance Summary

---

• Scott-Brown's Otorhinolaryngology Head & Neck Surgery (Vol 1 & 2), pp. 1014-1015, 285
• Cummings Otolaryngology Head and Neck Surgery, pp. 565-566
• KJ Lee's Essential Otolaryngology, pp. 517-518, 584
• Color Atlas of Human Anatomy Vol. 2, pp. 175-176

---

Constrictors of the Pharynx and Killian's Dehiscence (Zenker's Diverticulum)

---

PART 1: CONSTRICTORS OF THE PHARYNX

Overview

• Outer circular layer: three constrictor muscles (superior, middle, inferior) - they overlap like stacked flower pots, with each lower muscle overlapping the upper border of the one below
• Inner longitudinal layer: palatopharyngeus, stylopharyngeus, salpingopharyngeus

---

1. Superior Constrictor

• Passavant's ridge: a visible soft-tissue projection formed by contraction of the superior end of the superior constrictor during swallowing; it can be seen endoscopically and plays a role in velopharyngeal closure
• The glossopharyngeal nerve (CN IX) passes under the free edge of the superior constrictor, lying just deep to the palatine tonsil
• The palatopharyngeal sphincter lies on the deep surface of the superior constrictor
• The superior constrictor does not reach the skull base - the gap above it is filled by the pharyngobasilar fascia

---

2. Middle Constrictor

• The muscular anterior wall is incomplete between the middle and inferior constrictors - this gap is covered by the thyrohyoid membrane. The internal laryngeal nerve and superior laryngeal artery and vein pass through this membrane on its superolateral aspect. - Scott-Brown's, p. 788

---

3. Inferior Constrictor

• Distinctively different from all other constrictors - it is thicker, rounder, and its horizontal fibers create a true sphincter
• Acts as the upper esophageal sphincter (UES)
• Is in tonic contraction at rest (keeps the esophageal inlet closed, prevents air from entering during respiration)
• Actively dilates (relaxes) during swallowing - triggered by laryngeal elevation
• Is continuous below with the circular muscular coat of the upper esophagus
• The narrowest point of the pharyngeal cavity is the inferior constrictor's attachment to the cricoid cartilage

• The recurrent laryngeal nerve + inferior laryngeal artery and vein pass upward deep to the lower margin of the inferior constrictor - Scott-Brown's, p. 788

---

Constrictor Overlap Arrangement

• Inferior constrictors overlap the lower margins of the middle constrictors
• Middle constrictors overlap the lower margins of the superior constrictors

---

PART 2: KILLIAN'S DEHISCENCE AND ZENKER'S DIVERTICULUM

Killian's Dehiscence - Anatomy

• Superiorly: oblique fibers of thyropharyngeus (upper part of inferior constrictor)
• Inferiorly: horizontal fibers of cricopharyngeus (lower part of inferior constrictor)

---

Zenker's Diverticulum (Pharyngeal Pouch)

---

Epidemiology

• Incidence: 0.47-1 per 100,000 per year
• Predominantly affects Caucasians (rare in Asian and Afro-Caribbean races)
• Male:female ratio ~2:1
• Almost exclusively patients over 50 years, most commonly 6th-9th decade
• A true false diverticulum - wall consists of mucosa and submucosa only (no muscle)

---

Pathogenesis / Aetiology

Theory 1 - Anatomical weakness (Killian's dehiscence)

Theory 2 - Failed relaxation of cricopharyngeus

• Fibrosis (Cook's theory - laryngopharyngeal reflux as a cause)
• Muscle spasm (Negus, Sutherland, Belsey)
• Weakening of prevertebral fascia with age (Dohlman & Mattson) - the larynx falls forward, decreasing the circumference that cricopharyngeus is stretched across, creating functional obstruction

Theory 3 - Incoordination of pharyngeal muscles

• Oropharyngeal contraction is weak
• Pharyngeal peristaltic wave is weak
• Premature closure of cricopharyngeus occurs before the stripping wave reaches it

---

Growth and Expansion of the Pouch

• Initially the pouch expands posteriorly, but prevertebral fascia limits this direction
• Larger pouches project laterally and inferiorly, predominantly to the left side (the more exposed side)
• A very large pouch can push the esophagus to one side, sitting in line with the pharynx and causing severe dysphagia
• Contents can spill into the larynx, causing aspiration pneumonia

---

Clinical Features

• Rapidly increasing dysphagia
• Pain
• Blood in regurgitated food
• Neck mass or nodes

---

Pathology (Histology)

• Stratified squamous epithelium lining
• Submucosa (no muscular layer = false diverticulum)
• Surrounding fibrous tissue
• Scanty muscle fibers near the neck of the pouch
• Evidence of myositis in some patients (isolated or part of systemic disease)

---

Diagnosis

---

Management Options

1. Conservative

• Patients with minimal symptoms or unfit for surgery
• Dietary modification, positional manoeuvres

2. Endoscopic Surgery (preferred in elderly/frail - short anaesthetic, minimal intervention)

3. External (Open) Surgery

---

Summary Table: Key Spaces at the Inferior Constrictor

---

• Scott-Brown's Otorhinolaryngology Head & Neck Surgery (Vol 3), pp. 788, 855-859
• KJ Lee's Essential Otolaryngology, pp. 669, 833
• Gray's Anatomy for Students, p. 1182
• Yamada's Textbook of Gastroenterology

---

White Matter of the Brain: Classification and the Internal Capsule

---

PART 1: CLASSIFICATION OF WHITE MATTER OF THE BRAIN

---

I. PROJECTION FIBERS

---

II. COMMISSURAL FIBERS

---

III. ASSOCIATION FIBERS

A. Short Association Fibers (U-fibers / arcuate fibers)

• Connect adjacent gyri within the same lobe
• Form a "U" shape dipping under the sulcus between gyri
• Located just beneath the cortical gray matter
• Most superficial of all white matter

B. Long Association Fibers (Named Fasciculi)

C. Sub-cortical Capsular Fibers (also association type)

• External capsule: between claustrum and putamen
• Extreme capsule: between claustrum and insular cortex
• Kaplan & Sadock's, pp. 202-203

---

PART 2: THE INTERNAL CAPSULE

Definition

---

Shape and Position (Horizontal/Flechsig Section)

• Medial: Caudate nucleus (head) and Thalamus
• Lateral: Lenticular nucleus (Putamen + Globus pallidus)

---

Five Segments and Their Contents

1. Anterior Limb (Lenticulocaudate Segment)

• Boundaries: Between the lenticular nucleus (lateral) and the head of the caudate nucleus (medial)
• Length: ~2 cm
• Fibers:
  • Frontopontine fibers (frontal lobe → pontine nuclei)
  • Anterior thalamic radiation (thalamocortical and corticothalamic fibers connecting thalamus ↔ frontal cortex)
  • Caudate-putaminal fibers

2. Genu ("Knee")

• At the bend between anterior and posterior limbs, at the level of the interventricular foramen of Monro
• Fibers:
  • Corticobulbar (corticonuclear) tract - upper motor neuron fibers to cranial nerve nuclei in the brainstem
  • Corticoreticular fibers (to bilateral brainstem reticular formation)
  • Some motor corticopontine fibers

Clinical pearl: The genu syndrome (isolated genu infarct) produces facial and lingual hemiparesis with mild limb involvement because corticobulbar fibers predominantly serve the face and tongue. - Localization in Clinical Neurology, p. 31

3. Posterior Limb (Lenticulothalamic Segment)

• Boundaries: Between the lenticular nucleus (lateral) and the thalamus (medial)
• Length: ~3-4 cm (the largest segment)
• Fibers (anterior to posterior):
  • Corticopontine fibers (anterior part)
  • Corticospinal tract (caudal half) - somatotopically organized:
    • Upper extremity fibers more anterior (shoulder → elbow → wrist → fingers)
    • Followed by trunk fibers
    • Lower extremity fibers more posterior (hip → knee → ankle → toes)
    • Bladder and rectum fibers most posterior
  • Superior thalamic radiation (includes somatosensory radiation - VPL/VPM thalamus → somatosensory cortex)
  • Corticorubral fibers (to red nucleus)
  • Corticothalamic fibers

4. Retrolenticular Segment

• Position: Behind (posterior to) the lenticular nucleus
• Fibers:
  • Optic radiation (Gratiolet's radiation / geniculocalcarine tract): Lateral geniculate nucleus (LGN) → primary visual cortex (calcarine cortex)
  • Corticotectal fibers (to superior colliculus)
  • Corticonigral fibers (to substantia nigra)
  • Corticopontine fibers (parieto-occipito-temporo-pontine)

5. Sublenticular Segment

• Position: Inferior to the lenticular nucleus
• Fibers:
  • Auditory radiation (inferior thalamic peduncle): Medial geniculate nucleus (MGN) → primary auditory cortex (Heschl's gyri, superior temporal gyrus)
  • Temporopontine fibers
  • Some visual radiation fibers

---

Blood Supply

• Localization in Clinical Neurology, p. 31

---

3D Spatial Relationships

---

Clinical Significance

---

Summary Table: Internal Capsule

---

• Localization in Clinical Neurology, 8th Edition, pp. 31-32
• Neuroanatomy through Clinical Cases, 3rd Edition, pp. 256-257, 771-772
• Kaplan & Sadock's Comprehensive Textbook of Psychiatry, pp. 197-203
• Gray's Anatomy for Students, pp. 1302-1303
• Bradley and Daroff's Neurology in Clinical Practice, pp. 3297-3316