The superior transvelar approach to the fourth ventricle and brainstem

The fourth ventricle is usually approached using either the transvermian (median suboccipital) or the telovelar approach.1 These “Standard” posterior fossa surgeries are not to be taken lightly. Posterior fossa surgery carries 31.8% chance of complications, which include: new neurological deficit, posterior fossa syndrome, cerebrospinal fluid leak, meningitis, and wound infection.2 The mortality rate for posterior fossa surgery is 2.6%.2 Although the mutism part of the posterior fossa syndrome is reversible, this mutism is the reversible part of a “persistent neurologic syndrome.”3 The above-mentioned complications are partly due to the pathology itself, its nature, and location, but partly due to the surgical approach selected for the pathology. Surgical dissection of the suboccipital region carries higher rates of CSF leak and meningitis, compared with supratentorial craniotomies.4 Also, although the exact mechanism of the posterior fossa syndrome remains unknown,3 splitting the vermis has been proposed as the cause of at least the mutism part of this syndrome.5 Using the telovelar approach may minimize vermis resection; however, it still might require retraction of this delicate structure.1 Part of the rationale for the current study, is trying to decrease these complication rates by changing the surgical approach selected for a certain posterior fossa lesion. Instead of using the suboccipital route, for a fourth ventricular pathology, we used the occipital (or parietal) transtentorial approach. Also, there may come times, in which, a fourth ventricular pathology, would be best approached from above. For example, a pontine cavernous malformation, with its superficial part in the floor of the fourth ventricle (Fig. 1), will be best approached from above. This selection of approach is based on “The two-point method, for brainstem lesions.”6 The two-point method, selects the surgical approach to brainstem lesions that provides the best exposure, while minimizing tissue retraction. In this system, a line is drawn from the center point of the lesion (point 1) through the superficial point (point 2) and out, toward the skull, subcutaneous tissues, and skin. This line dictates the best approach to be used for resection of the lesion.6 Figure 1 “The two-point method” for brainstem lesions.”6 The two point method, selects the surgical approach to brainstem lesions that provides the best exposure, while minimizing tissue retraction. In this system, a line is drawn from ... We present the superior transvelar approach (Fig. 2) to the fourth ventricle, which accesses the fourth ventricle through the superior medullary velum. The superior transvelar approach uses the interhemispheric transtentorial or supracerebellar infratentorial routes to approach the posterior incisural space. Following an incision in the tentorium, the superior medullary velum is exposed between the lingula of the cerebellum and the inferior colliculus. No venous structures are involved in this approach, and the trajectory is usually 1 or 2 cm below the vein of Galen complex. Following an incision in the superior medullary velum, the fourth ventricle is accessed, revealing its floor, the superior and middle cerebellar peduncles, and the inferior medullary velum, from above. Figure 2 The superior transvelar approach. Following dissection of the cerebello-mesencephalic fissure (1), the microsurgical anatomy of the superior medullary velum (2), and the two superior cerebellar peduncles are exposed, (3) the fourth ventricular floor, ... Approaching the fourth ventricle or the brainstem by splitting the superior medullary velum has been mentioned in the literature, and is probably performed in many institutes around the world.7,8 However, a detailed description of this approach, the extent of fourth ventricle exposure gained, its advantages, disadvantages, pitfalls, and anatomical landmarks encountered, has not been performed until this date.