Draf III extension in the endoscopic endonasal transethmoidal, transcribriform approach through the back wall of the frontal sinus: a cadaveric study

OBJECTIVE: The Draf III (modified endoscopic Lothrop) has been proposed to extend the endonasal transethmoidal, transfovea ethmoidalis and transcribriform approach through the back wall of the frontal sinus. The exposure is time-consuming, increases the risk of cerebrospinal fluid (CSF) leak and the indications for use are not well-described. There is little data quantifying the advantage it conveys over the approach without the Draf III.
METHODS:
An endoscopic, endonasal transfovea, transcribriform approach was performed in 5 fresh, injected cadaver heads. Anatomic boundaries and measurements of the exposure were compared before and after addition of a Draf III. Pre- and post- dissection CT scans were obtained and additional radiographic measurements were made to quantify the additional exposure provided by the Draf III. Two clinical cases are presented where a Draf III was utilized.
RESULTS:
Radiographic measurements: The mean anterior to posterior boundary from frontal sinus to planum sphenoidale pre-Draf III was 3.0 cm and post-Draf III was 3.8 cm with an average change of 0.8 cm. Cadaveric measurements: Following the Draf III, the mean anterior to posterior boundary from the posterior wall of frontal sinus to the planum sphenoidale increased from 3.0 cm to 4.3 cm. Average increase of 1.3 cm with an average increased area of view of 1.79 cm2.
CONCLUSIONS:
This study quantifies the increase field of view provided by the Draf III during anterior skull base dissection. Recommendations for pre-operative examination of radiographic evidence are provided to help identify which individuals would benefit from the additional exposure.