A Novel Minimally Invasive Approach to the Middle Cranial Fossa: Surgical Technique and Clinical Outcomes

Background: Middle fossa craniotomy is an established surgical approach to manage lateral skull base pathology, such as superior canal dehiscence (SCD) or tegmen defects resulting in encephalocele and/or cerebrospinal fluid (CSF) leak. Traditionally described surgical incisions for MFC consist of a straight or curved pre-tragal vertical incision, or a large “C-shaped” incision, designed to facilitate a craniotomy of ~5x5cm (25cm2). Such an approach maximizes surgical exposure at the cost of a large incision and potential cosmetic deformity. In an attempt to optimize cosmetic outcomes in non-tumor MFC surgery, we have designed a minimally invasive approach characterized by a horizontally oriented S-shaped incision placed entirely within the hair-bearing skin, an anteroinferiorly based temporalis muscle flap, and small craniotomy. We hypothesize that our minimally invasive approach provides adequate exposure for management of non-tumor lateral skull base pathology with minimal postoperative morbidity.

Methods: Single surgeon, single institution retrospective case series. All patients who underwent a minimally invasive MFC for non-tumor indications from 2012 to 2016 were examined. Patient demographics, operative notes, and all clinical notes were reviewed. Intraoperative photos and video recordings were examined. Patients with less than three months clinical followup were excluded.

Results: 61 patients underwent 65 MFC procedures. Primary indication for surgery was SCD in 38 cases and CSF leak / encephalocele in 27 cases. Average craniotomy area was 10.4 ± 4.9 cm2. Visualization and plugging of the superior canal was achieved in all SCD cases and satisfactory repair of the skull base defect was achieved in all CSF leak / encephalocele cases. There were no cases where the incision had to be converted intraoperatively to a larger traditional approach. Endoscopic assistance was used to facilitate visualization of the skull base in 34/65 (52%) of procedures. A middle fossa retractor was used to retract the temporal lobe in 26/65 (40%) of procedures. Average follow-up was 12.6 ± 9.3 months. There were no instances of postoperative incision dehiscence, alopecia, or infection requiring reoperation or hardware removal. There were no major complications such as facial palsy, permanent severe hearing loss, meningitis or stroke.

Discussion: When performing MFC, a minimally invasive incision with small bony flap is sufficient for addressing non-tumor pathology of the lateral skull base. Competence with the endoscope facilitates this approach by allowing visualization of distal or downsloping defects through a smaller bony window. Our approach allowed for safe access in all cases of SCD and tegmen repair, while maximizing aesthetic outcome through a smaller skin incision hidden entirely behind the hairline. We found no major short or long-term complications associated with this technique.