Surgery of peritorcular meningiomas: the structural basis for preservation of torcular venous flow

OBJECTIVE Surgical removal of torcular meningiomas is a considerable challenge. The authors studied the anatomical structure of the torcula to identify a dissecting plane that allows for the removal of the tumor while maintaining the integrity and patency of the venous component. Here, they describe the anatomy and surgical technique applied in a cohort of patients with torcular meningiomas. METHODS In four formalin-fixed cadavers, the architecture of the torcula and connecting sinuses was studied using various stains. Accordingly, the authors categorized meningioma invasion of the torcula into different types based on the integrity of the venous component. They described the corresponding surgical techniques and retrospectively analyzed the medical records of a series of 14 patients with torcular meningiomas operated on between 1997 and 2018. RESULTS The histological preparation revealed that the torcular wall consists of two distinct compartments, an inner venous structure with a layer of endothelium surrounding the lumen, supported by an extra-endothelial layer composed of elastic fibers associated with multiple layers of thin smooth muscle fibers. Surrounding this inner venous structure is the dural fibrous structure. Between the dural fibrous component and the venous component, there is a collagenous layer that forms a cleavage plane, facilitating delamination. This cleavage made it possible to resect the tumor and maintain the integrity of the venous wall and venous flow. Based on the anatomical involvement of the torcular wall, the authors categorized torcular meningiomas into four types. Fourteen patients were managed based on this classification. In types I and II, the venous compartment is intact, flow is maintained, and the surgical technique for removing the tumor is described. In types III and IV, the tumor has disrupted the venous compartment and flow, and these tumors were removed with utmost care for preservation of collateral venous channels. CONCLUSIONS The anatomical composition of the torcular wall provides a plane of dissection to remove torcular meningiomas with preservation of venous channels and flow in cases in which the inner venous wall is not disrupted (types I and II). Tumors with occlusion of the torcula (types III and IV) mandate preservation of venous collaterals.