INTRACAVERNOUS INVAGINATION OF PITUITARY- ADENOMAS

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 usual ly evoked on CT-scan and MRI. In our study, it was confirmed in only o ne 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 sinsuses (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 abscence of any rupture of the medial wall of the CS. The medial wall of the CS i s, in fact, constituted by a dural pouch which close-fits the pituitar y gland and its expansions; its invaginates more or less in the CS, de pending on the importance of the pituitary lateral expansion. In case of a large adenoma, the finger-glove lateral distension of the pouch d isappears progressively during the tumoral removal. Finally the dura r eturns to its normal place back, at the end of the procedure. This con cept of invagination of the CS medial wall, as opposed to that of inva sion and therefore of rupture of the dural plane, explains the wide ra nge of figures concerning the frequency of intra-cavernous invasion by pituitary adenomas, in the literature. These figures are all the more variable as there is not absolute criteria of intra-cavernous invasio n 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 ophtha lmoplegia seems to be usually linked to a compression of oculomotors n erves; it recovers in a large majority of cases, after the adenoma is removed. In conclusion, we emphasize the necessity of interpreting wit h great care radiological imaging when it evokes a possible intra-cave rnous invasion of a pituitary adenoma. The indication of an eventual r adiotherapy should be retained with as much care as possible, since co mplete removal of an adenoma and its lateral expansion(s) is almost al ways feasible through a trans-sphenoidal route.