Unlocking the Middle Fossa: A 360-Degree View

Objective: The author defines “unlocking the middle fossa” (UTMF) as a series of operative steps leading to sectioning the meningo-orbital band with extradural exposure of the clinoid process. Depending on the required exposure, additional surgical maneuvers—including clinoidectomy, dissection of the temporal dura propria from the cavernous sinus, and anterior petrosectomy—can be performed. While numerous publications describing individual extensions of this approach exist in the literature, there is a paucity of information describing the overall versatility and range of pathology that can be addressed. In this lecture, operative cases are reviewed to define the utility of the UTMF.

Methods: The authors retrospectively reviewed the operative notes of a consecutive database of procedures in which UTMF was performed as a component of surgery. The cases were classified into 1 of 4 phases, depending on the required exposure after the middle fossa had been unlocked. Phase 1 was used to treat pathology in the anterior fossa, orbit, clinoid and paraclinoid regions. Phase 2 was used in cases in the cavernous sinus or middle fossa. Phase 3 involved the posterior fossa or petroclival region. The pathology located in the infratemporal fossa was treated with UTMF phase 4. Standardized pre- and postoperative clinical and radiological parameters were assessed. A clinical and anatomic correlation is done during the lecture to clarify the advantage of the approach as well as the use of anatomical landmarks. Multiple full HD videos are exposed for each of the phases of the UTMF approach.

Results: Between January 2014 and August 2018, a total of 72 patients (18 M, 54 F) aged 8 to 74 years underwent a total of 72 UTMF surgeries by the primary author (DMR). The most frequent treated histopathology was meningioma (n = 41). The 72 cases were further stratified by phase: 37 as phase 1, 15 as phase 2, 13 as phase 3, and 7 as phase 4.

Conclusion: UTMF is an essential operative technique that provides access to a wide variety of pathologies of the skull base. Knowledge of the versatility of this approach should be essential components of education for all neurosurgical trainees.

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