The Extended Minipterional Approach: A Modification to Approach the Insular Region

Background: For its versality and wide acceptance, the pterional craniotomy has become the mainstay of treatment for most of the anterior circulation aneurysms, parasellar lesions and tumors located in the anterior cranial fossa. Minipterional approach (MPTa) was introduced as a less invasive alternative to treat anterior and middle fossa lesions and anterior circulation aneurysms. As in other minimally invasive approaches, the MPT offers better cosmetic results, protection of the underlying brain parenchyma, shorter operative times, and less soft tissues injury. Nonetheless, soon after its first description, several authors raised their concerns regarding the reduced surgical freedom of movement and the limited operative view using the MPTa. In fact, one limitation of the MPTa is the reduced exposure of the distal Sylvian fissure, which preclude a wide dissection, limiting the access to lesions located deep at the Sylvian cistern.

We describe a modification of the MPTa, the extended minipterional approach (eMPTa), that improves access to the distal Sylvian fissure with minimal additional bony removal. We define the ideal posterior landmark for this craniotomy based on an anatomic cadaveric study.

Methods: Insular and sylvian linear exposure offered by the MPTa and eMPTa were compared among 6 heads of cadaveric specimens. Surgical anatomy of the eMPTa and its relationship with representative neurovascular landmarks were also evaluated.

Results: By minimally expanding the bone removal up the preauricular line, the eMPTa affords a threefold increase in the linear exposure of the insular and linear exposure (p = 0.001 and p < 0.001, respectively). The frontal precentral artery, an important landmark for performing a distal-to-proximal Sylvian dissection, is 17 ± 5.2 mm anterior to the preauricular line, the posterior limit of the eMPTa, whereas it is 6.5 ± 3.6 mm posterior to pterion, the posterior limit of the MPTa.

Conclusion: The eMPTa provides an increased sylvian and insular exposure while maintaining a minimally invasive approach. Importantly, this bony expansion achieved an expanded insular view that offers potential increasing applications to vascular (i.e., giant MCA aneurysms, thalamic cavernous malformation) and neoplastic (i.e., insular gliomas) pathologies that are classically treated via a pterional approach. Potential disadvantages of this technique, in comparison to the classic MPTa, are the use of a larger skin incision and the risk of damaging certain eloquent areas given the increase in the brain exposure (i.e., Broca's area in the left side).