Residency · Residency · Otolaryngology
Anterior Skull Base: Endoscopic Approaches
Introduction
The anterior skull base represents the floor of the anterior cranial fossa and the roof of the sinonasal cavity. Advances in endoscopic endonasal surgery have revolutionized the management of lesions in this region, offering reduced morbidity compared to traditional open craniofacial approaches. Mastery of endoscopic skull base anatomy and reconstruction techniques is essential for the modern otolaryngologist-head and neck surgeon.
Anatomy of the Anterior Skull Base
Bony Framework
Cribriform plate: thin, perforated bone transmitting olfactory nerve filaments. Fovea ethmoidalis: lateral roof of the ethmoid sinuses; variable height (Keros classification I-III). Planum sphenoidale: flat roof of the sphenoid sinus, continuous posteriorly with the sella turcica. Crista galli: midline vertical projection serving as the anterior attachment of the falx cerebri.
Vascular Supply
Anterior ethmoidal artery (AEA): branch of the ophthalmic artery; courses through the skull base at the junction of the fovea ethmoidalis and cribriform plate. Posterior ethmoidal artery (PEA): located 12-15 mm posterior to the AEA. Critical to identify and control these vessels to prevent retraction into the orbit and orbital hematoma.
Key Relationships
The lateral lamella of the cribriform plate is the thinnest and most vulnerable area. Keros Type III (deep olfactory fossa) carries the highest risk of iatrogenic CSF leak.
Pathology of the Anterior Skull Base
| Pathology | Key Features | Typical Management |
|---|---|---|
| Esthesioneuroblastoma | Kadish staging A-D; olfactory origin | Endoscopic resection +/- adjuvant RT |
| SNUC | Aggressive, poorly differentiated | Multimodal (surgery + CRT) |
| Sinonasal SCC | Most common sinonasal malignancy | Surgery +/- adjuvant RT |
| Meningioma | Benign but locally invasive | Endoscopic or open resection |
| Encephalocele/CSF leak | Non-neoplastic; meningitis risk | Endoscopic repair |
| Fibrous dysplasia/osteoma | Benign bony lesions | Observation or surgical debulking |
Esthesioneuroblastoma (olfactory neuroblastoma): Kadish staging A-D. Sinonasal undifferentiated carcinoma (SNUC). Sinonasal squamous cell carcinoma. Meningiomas extending into the sinonasal cavity. Encephaloceles and CSF leaks. Fibrous dysplasia and osteomas.
Endoscopic Endonasal Approach: Technique
Preoperative Planning
High-resolution CT and MRI with contrast for tumor extent and vascular involvement. Image-guided navigation (IGS) is strongly recommended, Multidisciplinary planning with neurosurgery.
Surgical Steps
Posterior septectomy to create a binostril working corridor. Complete bilateral ethmoidectomy and wide sphenoidotomy. Identification of critical landmarks: AEA, PEA, optic nerve, carotid artery. Drilling of the skull base to define bony margins of the lesion. Dural incision and tumor resection with margin assessment. Reconstruction of the skull base defect.
Skull Base Reconstruction
Nasoseptal flap (Hadad-Bassagasteguy flap): workhorse vascularized flap based on the posterior septal artery. Multilayer reconstruction: collagen matrix inlay, fascia lata, nasoseptal flap overlay. Lumbar drain placement for high-flow CSF leaks (controversial).
Complications
CSF leak: most common major complication (5-15% in large series). Meningitis: risk increases with persistent CSF leak. Anosmia: near-universal with cribriform resection. Orbital injury: hematoma, diplopia, vision loss. Vascular injury: carotid artery, anterior ethmoidal artery. Pneumocephalus: tension pneumocephalus is a surgical emergency.
Outcomes
Endoscopic approaches demonstrate comparable oncologic outcomes to open craniofacial resection for selected tumors. Lower rates of wound complications, frontal lobe retraction injury, and ICU stay. Negative margins remain the most important prognostic factor.
Key Clinical Pearls
Always harvest the nasoseptal flap early before performing posterior septectomy, even if reconstruction may not be needed. Keros classification should be reviewed on every preoperative CT to anticipate skull base height asymmetry. The anterior ethmoidal artery is the most commonly injured vessel during endoscopic skull base surgery. A multidisciplinary team approach (otolaryngology and neurosurgery) improves outcomes and safety. Postoperative nasal packing and head-of-bed elevation reduce CSF leak rates.
References
- Snyderman CH, Carrau RL, Kassam AB, et al. Endoscopic skull base surgery: principles of endonasal oncological surgery. J Surg Oncol. 2008;97(8):658-664.
- Hadad G, Bassagasteguy L, Carrau RL, et al. A novel reconstructive technique after endoscopic expanded endonasal approaches: vascular pedicle nasoseptal flap. Laryngoscope. 2006;116(10):1882-1886.
- Devaiah AK, Andreoli MT. Treatment of esthesioneuroblastoma: a 16-year meta-analysis of 361 patients. Laryngoscope. 2009;119(7):1412-1416.
- Harvey RJ, Parmar P, Sacks R, Zanation AM. Endoscopic skull base reconstruction of large dural defects: a systematic review of published evidence. Laryngoscope. 2012;122(2):452-459.