Frontal Sinus “Hump”: An Anatomical Risk Factor for Anterior Skull Base Injury in the Endoscopic Modified Lothrop Approach (Outside-In Frontal Drill-Out)

Figure 3

Surgical image presentation. (a) The endoscopic modified Lothrop procedure (EMLP) on the right side. The first olfactory fibre was identified (white arrow), and the right frontal beak was drilled out (white dotted line). (b) The posterior wall of the right frontal sinus was identified, the floor of the frontal sinus (white dotted line) was drilled out, and the left frontal sinus was approached. The first olfactory fibre is visible (white arrow). (c) After drilling out the floor of the frontal sinus. The first olfactory fibre on the left side (tumour side) is identified (yellow arrow), and a space was observed (white triangle) on the left side at the same depth as the right frontal sinus. (d) The space was drilled out to open by 4 mm (white triangle); leakage of cerebrospinal fluid was observed. The first olfactory fibre (white and yellow arrow). (e): The EMLP was finished. Bilateral frontal sinuses were observed; it was confirmed that the posterior wall of the left frontal sinus was damaged (white triangle). The first olfactory fibre (white and yellow arrow). (f) After anterior cranial resection of an olfactory neuroblastoma. The injured area of the skull base overlapped with the resected area of the tumour. (g) The skull base was reconstructed to be water-tight by suturing the dura mater to the fascia. (h) Multilayer reconstruction using fascia and cartilage. (i) Finally, the wound was covered with a nasoseptal flap.