Depending on authors, intra-cavernous invasion by a pituitary adenoma is found in 9% to 40% of cases. In the light of our own experience, we think that such an invasion is probably much less frequent than usually evoked on CT-scan and MRI. In our study, it was confirmed in only one case over 125 (0.80%), though radiological data suspected an intra-cavernous invasion 17 times. An anatomical study on 20 cadavers showed that 30% of normal pituitary glands present with a lateral expansion into one or both cavernous sinuses (CS). These natural invaginations were already evoked by Harris and Rhoton in 1976. They can resemble an intra-cavernous extension or invasion on MRI views, moreover when an adenoma increases the volume of this expansion, and in the absence of any rupture of the medial wall of the CS. The medial wall of the CS is, in fact, constituted by a dural pouch which close-fits the pituitary gland and its expansions; it invaginates more or less in the CS, depending on the importance of the pituitary lateral expansion. In case of a large adenoma, the finger-glove lateral distension of the pouch disappears progressively during the tumoral removal. Finally the dura returns to its normal place back, at the end of the procedure. This concept of invagination of the CS medial wall, as opposed to that of invasion and therefore of rupture of the dural plane, explains the wide range of figures concerning the frequency of intracavernous invasion by pituitary adenomas, in the literature. These figures are all the more variable as there is no absolute criteria of intra-cavernous invasion on CT-scan nor MRI views. In the same way, no clinical criteria can be retained to assume the existence of such an invasion. So, an ophthalmoplegia seems to be usually linked to a compression of occulomotors nerves; it recovers in a large majority of cases, after the adenoma is removed. In conclusion we emphasize the necessity of interpreting with great care radiological imaging when it evokes' a possible intra-cavernous invasion of a pituitary adenoma. The indication of an eventual radiotherapy should be retained with as much care as possible, since complete removal of an adenoma and its lateral expansion(s) is almost always feasible through a trans-sphenoidal route.