Purpose: The parasellar region is a small but complex structure, and a large variety of tumors arise from this region. Postoperative morbidity for these tumors depends significantly on the cranial nerves located in the lateral part of this parasellar region. The aim of this study is to understand the anatomical structures of the lateral parasellar region and describe the inter-dural approach for parasellar tumors. Methods: To understand the anatomical structure, microsurgical dissection of both sides of six cadaveric heads and histological study of three cadaveric heads were performed. Based on our findings, a less invasive, inter-dural approach is demonstrated with our experiences of cases with parasellar tumors. Results: The dura mater of the middle cranial fossa consists of periosteal and meningeal dura. In the parasellar region (medial to trigeminal nerve branches), these two layers are separated, composing an inter-dural space. The cranial nerves, cavernous sinus and carotid artery are located in this inter-dural space. Cranial nerves are surrounded by a membrane, a so-called inner layer. The cavernous sinus is separated from the cranial nerves by this inner layer. It is an important notion that a periosteal incision along the inferior margin of the cavernous sinus in the middle cranial fossa allows an approach to the trigeminal nerve and cavernous sinus without intrusion into the subdural space and injury of nerves and vessels. Conclusions: Considering anatomical and histological study and our clinical experiences, this inter-dural approach is practicable and useful for surgical removal of the tumors such as trigeminal neurinoma and cavernous hemangioma.
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