The aim of this study was to clarify pathological and anatomical relationships between adamantinomatous craniopharyngiomas (ACP) and their surrounding structures. We previously established a QST classification scheme based on the apparent anatomic origin of the tumors. According to this classification, 13 type Q tumors, 6 type S tumors, and 42 type T ACPs were analyzed. Type Q tumors, which are most likely to involve the pituitary gland, did not invade the area of contact with the adenohypophysis. Instead, tumor invasion was observed in areas where the tumor contacted the neurohypophysis. Type S tumors primarily involved the pituitary stalk; the arachnoid remained present between these tumors and normal structures. Type T tumors were located beneath the basal arachnoid membrane and outside the pia mater. The pia mater was disrupted and finger-like invasions were found in the neural layer of the third ventricle floor along the invasive front. Tumors were never observed to break through the ependymal layer of the third ventricle. The QST classification has important implications for understanding the growth pattern of tumors and can be used to guide surgical procedures.