Functional Endoscopic Sinus Surgery (FESS)

1. Definition & Primary Objective

• Remove irreversibly diseased mucosa and bone
• Preserve normal tissue and mucosal lining (skull base, lamina papyracea, sinus cavities)
• Judiciously widen the true natural ostia of the sinuses
• Leave uninvolved sinuses alone

2. Historical Background

3. Indications

• Chronic Rhinosinusitis (CRS) — with or without nasal polyps (CRSwNP / CRSsNP)
• Allergic fungal sinusitis (AFS)
• Recurrent acute rhinosinusitis
• Complicated acute rhinosinusitis
• Mucocele or pyocele of sinuses
• Sinonasal polyposis
• Cystic fibrosis-related sinusitis
• Primary ciliary dyskinesia
• Orbital or intracranial extension of sinus disease (often urgent)

4. Preoperative Assessment

History

• Smoking
• Asthma
• Aspirin-exacerbated respiratory disease (Samter's triad)
• Allergies
• Immunodeficiency
• Depression

Physical Examination

• Complete head and neck examination
• Basic ocular examination
• Anterior rhinoscopy — detects septal deviation, nasal valve collapse
• Nasal endoscopy (rigid or flexible) — character of mucosa, sinus drainage pathways, purulent drainage, polyps, anatomic variations

Radiographic Assessment

• CT scan (non-contrast) — modality of choice; provides excellent bone detail; assesses sinonasal anatomy and disease extent; used for preoperative planning and image-guided navigation
• Lund-Mackay score — quantifies disease burden on CT
• MRI — indicated if bony dehiscence or erosion of skull base / lamina papyracea is present (to differentiate inflammatory disease from tumors or encephaloceles)
• CT should be obtained 3–4 weeks after maximal medical therapy to avoid operating on acute inflammatory changes

5. Key Anatomy Relevant to FESS

Osteomeatal Complex (OMC)

• Uncinate process
• Ethmoidal infundibulum
• Hiatus semilunaris
• Anterior ethmoidal cells
• Maxillary sinus ostium
• Frontal recess

Critical Landmarks

• Lamina papyracea — medial orbital wall; breach causes orbital fat herniation or orbital hematoma
• Skull base / fovea ethmoidalis — breach causes CSF leak
• Optic nerve — at risk in posterior ethmoid / sphenoid surgery
• Internal carotid artery — lies within the sphenoid sinus walls
• Keros classification of olfactory cleft depth determines skull base risk
• Asymmetry in ethmoid roof height — increases risk of intracranial penetration

6. Surgical Technique: Step-by-Step

Step 1 — Uncinectomy

• The uncinate process is the first structure removed
• A sickle knife or backbiter punch is used to detach it
• Retrograde uncinectomy: initiated at the junction of upper two-thirds and lower one-third, extending anteriorly to the anterior maxillary line (M)
• Removal exposes the ethmoidal infundibulum and the maxillary sinus ostium

Step 2 — Anterior Ethmoidectomy

• Anterior ethmoidal air cells (agger nasi, bulla ethmoidalis) are systematically opened
• The bulla ethmoidalis — the largest and most consistent anterior ethmoid cell — is opened
• A thorough ethmoidectomy with complete removal of cells is critical for successful maxillary antrostomy and frontal sinusotomy

Step 3 — Maxillary Antrostomy

• The maxillary ostium is elliptical and found in the floor of the infundibulum lateral to the lower third of the uncinate
• Requires a 30° or 45° angled endoscope for optimal visualization
• The ostium is gently dilated posteriorly with a maxillary sinus seeker
• Key principle: the antrostomy must incorporate the natural ostium — opening an accessory ostium while missing the natural ostium leads to mucus recirculation and persistent infection
• Any accessory ostia present must be incorporated into the antrostomy

Step 4 — Posterior Ethmoidectomy

• Posterior ethmoidal cells are entered by piercing the basal lamella (ground lamella) of the middle turbinate
• Care taken around the lamina papyracea and skull base

Step 5 — Sphenoidotomy

• The sphenoid sinus is accessed via the natural ostium (found ~1–1.5 cm above the choanal arch)
• Key risks: optic nerve (superolateral wall), internal carotid artery (lateral wall)

Step 6 — Frontal Sinusotomy (Draf Procedures)

• Draf I: removal of anterior ethmoidal cells that block frontal recess
• Draf IIA: unilateral frontal sinusotomy (medial to middle turbinate insertion)
• Draf IIB: removal of floor of frontal sinus from septum to lamina papyracea
• Draf III (modified Lothrop): bilateral Draf IIB with removal of upper nasal septum — creates single drainage pathway; maximum frontal exposure

7. Extent of Surgery

8. Image-Guided Surgery (IGS / Navigation)

• CT-based intraoperative navigation helps identify landmarks in complex or revision cases
• Particularly useful in: revision surgery, extensive polyposis, skull base or orbital wall dehiscence, anatomic distortion
• Does not replace surgical knowledge of anatomy

9. Postoperative Care

• Nasal saline irrigation — clears crusts and debris
• Intranasal corticosteroid sprays or rinses
• Endoscopic debridement in the office — removes crusts, adhesions, and residual secretions in the weeks following surgery
• Systemic steroids and antibiotics as indicated
• Detailed postoperative follow-up reduces adhesion formation and scarring

10. Complications

Minor Complications

• Bleeding / epistaxis
• Periorbital bruising or edema
• Adhesion formation (synechiae)
• Hyposmia / anosmia

Major Complications

11. Causes of Failure / Revision Surgery

Technical Failures (Surgical)

• Lateralized middle turbinate — obstructs the operated sinus
• Failure to incorporate maxillary ostium in middle meatal antrostomy → mucus recirculation
• Maxillary ostium stenosis
• Frontal recess scarring
• Residual ethmoidal air cells
• Adhesions / synechiae
• Unidentified Haller cells (infraorbital ethmoid cells) or Onodi cells (sphenoethmoid cells) causing persistent obstruction
• Incomplete uncinate removal

Disease-Related Failures

• Middle turbinate lateralization
• Neo-osteogenesis — new bone formation
• Recurrent nasal polyposis

Patient Conditions with Higher Revision Rates

• CRS with nasal polyps (CRSwNP)
• Allergic fungal sinusitis
• Disorders of mucociliary clearance (e.g., primary ciliary dyskinesia, cystic fibrosis)
• Underlying biofilms
• Immunodeficiencies
• Aspirin-exacerbated respiratory disease (AERD)

12. Outcomes

• FESS provides significant improvement in overall and disease-specific quality of life
• High success rate when combined with appropriate medical therapy
• Symptom improvement rates of 80–90% in well-selected patients for CRS
• Surgery must be coupled with lifelong postoperative medical management (especially in CRSwNP, AERD, AFS)

Summary