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Sphenoidotomy


Introduction

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    There are two ways to approach and perform a sphenoidotomy: transnasal and transethmoid.

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    In the transnasal approach, the sphenoidotomy is performed while sparing the ethmoid cavity. Dissection proceeds medial to the middle turbinate. Common indications for this approach are isolated pathologic processes within the sphenoid sinus (e.g., fungal ball, isolated sphenoid sinusitis). This approach may also be combined with a posterior septectomy for an endoscopic transnasal approach to the pituitary sella (see Chapter 28 ).

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    In the transethmoid approach, the uncinate process and inferior ethmoid air cells are removed to access the anterior face of the sphenoid sinus. This technique may be used in cases of isolated sphenoid disease, but most commonly is performed as a component of a complete functional endoscopic sinus surgery.

Anatomy

Sphenoid

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    The sphenoid sinus has the following borders ( Fig. 8.1 ):

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      Anterior: superior turbinate and posterior ethmoid cells

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      Medial: intersinus septum and nasal septum

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      Posterior: pituitary sella superiorly, clival recess inferiorly

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      Lateral: cavernous sinus, optic nerve, and infratemporal fossae

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      Superior: planum sphenoidale, anterior skull base

    Fig. 8.1, Schematic drawings of the sphenoid sinus showing sagittal (A) and axial (B) views of the structures involved in a sphenoidotomy (shaded area).

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    The natural os of the sphenoid sinus lies in the medial and inferior portion of the sphenoid face, nearly always medial and posterior to the superior turbinate ( Fig. 8.2 ).

    Fig. 8.2, Axial CT scan showing the position of the natural sphenoid os medial, posterior, and inferior to the superior turbinate.

Onodi Cell

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    An Onodi cell is a posterior ethmoid cell that lies superior or lateral to the sphenoid sinus.

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    When a sphenoidotomy is performed, it is crucial not to confuse the posterior wall of an Onodi cell with the anterior face of the sphenoid.

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    A common cause of optic nerve or orbital apex injury in the early days of functional endoscopic sinus surgery was dissection through the posterior wall of an Onodi cell because it was mistaken for the anterior face of the sphenoid sinus ( Fig. 8.3 ).

    Fig. 8.3, Coronal CT scans ( A and B ) revealing left Onodi cells. Note the location of the optic nerve in the roof of these cells.

Vasculature

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    The septal branch of the sphenopalatine artery runs horizontally along the inferior and anterior face of the sphenoid sinus.

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