Endoscopic Endonasal Exposure of the Lateral Portion of the Petrous Internal Carotid Artery: Importance of the Medial Edge of the Tympanic Plate

Background: Prior anatomic work has demonstrated the importance of the eustachian tube and sphenoid spine (SS) as landmarks for identification of the lateral petrous carotid artery (LPCA). However, there still remains intervening space from the SS to the carotid artery (ICA) that leaves room for error during exposure of the carotid.

Objectives: We undertook this study to identify a reliable landmark between the SS and introitus of the carotid canal with the Eustachian tube intact.

Study Design: Cadaveric study.

Methods: Eight fresh heads were dissected to identify pertinent anatomic features. Five embalmed, latex injected, cadaveric head were then dissected endonasally to demonstrate the regional anatomy of SS, tympanic plate and petrous ICA. Ten dry skulls were utilized to characterize the bone ridge between the SS and carotid canal introitus.

Results: With the eustachian tube remaining intact, a palpable bony ridge along the skull base is identified between the SS and LPCA. Using fixed heads, open dissection and dry skulls, this palpable ridge is determined to be the medial edge of the tympanic plate (mTP). From the endoscopic approach, the mTP is a palpable guide leading directly to the introitus of the carotid canal and can be used without disrupting the eustachian tube. In addition, the medial tympanic plate itself is the last landmark directly in front of the pharyngeal carotid. Surgical steps and anatomic photos using the mTP as a landmark are presented.

Conclusion: The SS has previously been described as a landmark for the pharyngeal carotid, but there is intervening space to the LPCA that leaves room error during dissection. This study identifies the mTP as a novel palpable boney ridge, which is the last landmark leading directly to the opening of the carotid canal.