LAUSR

Dear Editor, We have read with great interest the article entitled, BTranseyebrow supraorbital approach in large suprasellar craniopharyngioma surgery in adults: analysis of optic nerve length and extent of tumor resection^, published by Prat et al. [4] in Acta Neurochirurgica. The authors have retrospectively analysed the relationship between the optic chiasm position/ optic nerve length and the degree of tumour resection in a series of 21 craniopharyngiomas (CPs). Total tumour resection occurred in all patients with a postfixed chiasm but never when the chiasm was prefixed. Among the cases with a normal chiasm, the greater the length of the optic nerve, the higher the rate of tumour resection. With the present letter, we wish to clarify two basic concepts to take into account in CP surgery: (1) CP adherence to the hypothalamus is the major determinant of the likelihood of a safe radical resection; (2) the type of optic chiasm distortion caused by CPs is a factor related to both the primary tumour topography and its adhesion to the hypothalamus. Prat et al. [4] define the topography of all CPs included in their series with the highly imprecise term Bsuprasellar^, when they in fact describe that most tumours also involved the third ventricle. The major drawback associated with the ill-defined Bsuprasellar^ concept, a widespread and often misused term in the literature, is that it leads to the incorrect assumption of a position of the CPs beneath an intact hypothalamus. However, a large number of CPs originate from the infundibulum and expand within the hypothalamus itself, presenting strong adhesions to this vital structure, preventing a gross total removal. CP adherence to the hypothalamus, rather than to the optic chiasm/optic nerves, is the major pathological variable related to surgical outcome [3, 6]. A proper topographical classification system based on the original site of CP development along the vertical pituitary-hypothalamic axis, taking into consideration the degree of anatomical distortion/adherence of the third ventricle floor (TVF), has proved useful to predict the surgical risk associated with hypothalamic injury and patient outcome (Fig. 1) [2, 3]. In a recent paper, we systematically analysed the anatomical distortions CPs caused on the optic chiasm in a series of 150 cases [5]. A strong correlation between the type of chiasm distortion observed on preoperativeMRI and the definitive CP topography was found. Two major force vectors determining the types of chiasm distortion were identified: compression versus stretching. Compressed chiasms showing a crescent and swollen appearance against the tuberculum sellae (classically known as prefixed chiasms) are present with CPs developing at the level of the infundibulum and/or third ventricle (infundibulo-tuberal and strictly third ventricle CPs, respectively). Stretched chiasms showing a marked elongation and thinning occur with CPs developing below the infundibulum, either from the pituitary gland or from the pituitary stalk (Fig. 1). Primary sellar and Bsuprasellar^ CPs whose growth is restricted within the suprasellar (chiasmatic) cistern usually cause an upwardly stretched distortion of the chiasm, as the lesions expand predominantly against the undersurface of the optic apparatus. In contrast, those CPs invading the third ventricle from an original suprasellar position (secondary intraventricular CPs) usually cause a distortion of the chiasm that * Ruth Prieto [email protected]