Pneumatization degree of the anterior clinoid process: a new classification

Abstract

The objective of this study is to determine the incidence and degree of anterior clinoid process pneumatization, in addition highlighting to their clinical significance. Multidetector-row CT scans of the skull base were reviewed in 648 subjects between 2007 and 2008. The presence of pneumatized anterior clinoid process and its degree were studied and documented. These data were statistically analyzed. Pneumatization of the ACP was found in 62 of 648 patients (9.6%) including 32 (51.6%) men and 30 (48.4%) women. The age of these patients ranged from 21 to 82 years (mean, 41 +/- 15.7 years). Pneumatization of the ACP occurred only on the left side in 14 cases (22.6%), only on the right side in 11 cases (17.7%), and bilaterally in 37 patients (59.7%). ACP pneumatization Type I, in which less than 50% of the ACP is pneumatized, was found in 47 of 124 sides (38%), Type II, in which more than 50% but not totally pneumatized ACP, was found in 28 of 124 sides (22.6%), and Type III, in which the ACP is totally pneumatized, was found in 22 of 124 sides (17.7%). The incidence of Type I in the general population was 6.6%, Type II was 3.5%, and Type III was 2.5%. Radiologically recognizing the degree of ACP pneumatization is important in decreasing the incidence of surgical complications during anterior clinoidectomy. Proper intraoperative management can be undertaken with special attention to the new classification.

The pneumatisation of anterior clinoid process is not associated with any predictors that might be recognised preoperatively

“…The ACP is a bony structure covered by dense cortical bone. The anterior/ superior (roof of the optic canal) and posterior/inferior (optic strut) roots of the lesser sphenoid wing form the bases of the process [1,9,11]. The ICA is adjacent to the medial inferior part of the ACP.…”

“…the preoperative evaluation of ACP facilitates safer high--speed drilling and is recommended by practitioners [1,10]. Intraoperative neural or vascular damage occurs more often in pneumatised ACP than in osseous examples.…”

“…The incidence of pneumatised processes has been reported as ranging from 4% to 29.3% in several studies [1,4,5,14,20,21]. Thus, up to one in 3 resected ACPs should be assumed to have air cells accumulated within.…”

“…In patients afflicted with any of the aforementioned aneurysms, intraoperative extra-or intradural removal of the ACP (anterior clinoidectomy) is an essential manoeuvre to expose the aneurysm neck in order to ensure safe clip placement. Likewise, treatment of some supraclinoid aneurysms, basilar artery aneurysms, giant pituitary adenomas, and cavernous sinus lesions also require an anterior clinoidectomy, which is an important step in an extended neurosurgical approach [1,3,12,14,23,24]. In cases of suprasellar meningiomas, recurrent growth is prevented by removal of the bony tumour origin, including the ACP; therefore, an anterior clinoidectomy is also used in the treatment of such patients.…”

“…Apart from rhinorrhoea, anterior clinoidectomies increase the rate of oculomotor nerve paresis, injuries of ICA, ophthalmic artery and cavernous sinus, or intraoperative aneurysm rupture [2,6,18,22]. However, in recently published cadaveric and radiographic studies pneumatised ACPs pertained to a minority of patients and ranged from 4% to 29% of investigated cases [1,4,5,14,20,21].…”