Lateral skull base meningoencephalic herniations (MEH) are rare instances where dura mater (meningocele) or cerebral tissue (encephalocele) protrudes through skull base dehiscences, commonly in the tegmen tympani or mastoidium. Encephaloceles and cerebrospinal fluid (CSF) leaks carry great risk, as they provide a potential pathway from the middle ear to the subarachnoid space. Patients often present with non-specific clinical symptoms, so a high degree of clinical suspicion is needed, with a thorough radiologic assessment to confirm the diagnosis and location of bony defects. Early detection and surgical repair of encephaloceles or CSF leaks are imperative. Typical surgical approaches for lateral skull base encephaloceles are based on surgeon experience and include the transmastoid (TM), middle cranial fossa (MCF), and combined TM and MCF approach. In general, the TM approach is used for small defects, and for larger defects, the MCF or combined approach is typically the procedure of choice. When there is no possibility of hearing preservation or rehabilitation, a middle ear obliteration (MEO) can be considered as it has very low recurrence rates and provides definitive treatment. Our institution prefers the combined transmastoid and keyhole middle cranial fossa approach.

The transbasal approach has historically been a work-horse for access to lesions in the anterior fossa, orbit, nasal cavity, paranasal sinuses, pterygopalatine fossa, and pituitary fossa. When combined with a transfacial route, increased visualization and access is provided to deeper structures with minimal brain retraction and decreased risk to neural and vascular structures. Due to the complexity of this approach, oftentimes requiring multiple surgical teams participating, the decision to utilize it should be made on a case-by-case basis after a multidisciplinary discussion. This chapter discusses the indications, anatomical, and surgical details required to treat benign and malignant neoplasms involving the anterior skull base, paranasal sinuses, and potentially the orbits.