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Surgical management of paraclinoid aneurysms

How to cite this article: Magallón-Barajas E, Abdo-Toro M, Flores-Robles C. [Surgical management of paraclinoid aneurysms]. Rev Med Inst Mex Seguro Soc. 2016;54 Suppl 2:S132-9.



Received: November 2nd 2015

Judged: November 2nd 2016

Surgical management of paraclinoid aneurysms

Eduardo Magallón-Barajas,a Miguel Abdo-Toro,a Claudia Flores-Roblesa

aServicio de Neurocirugía, Hospital de Especialidades, Centro Médico Nacional Siglo XXI, Instituto Mexicano del Seguro Social, Ciudad de México, México

Communication with: Eduardo Magallón Barajas


Background: Paraclinoid aneurysms arise from C5 clinoid segment and C6 ophthalmic segment, within the internal carotid artery. Brain aneurysms have a frequency ranging from 5 to 11 %. A successful surgery requires knowledge of the anatomic region and the aneurysm. The objective was to show the surgical management of paraclinoid aneurysms.

Methods: From January 2009 to January 2015, we carried out a retrospective study in the Neurosurgery Department at Centro Médico Nacional Siglo XXI. We included 66 patients with the diagnosis of paraclinoid aneurysm. We obtained the clinical characteristics, evolution, complications, and outcomes from the clinical and radiological records.

Results: 61 patients (92.4 %) were female; 65 underwent neurosurgical clipping, and one underwent cerebral bypass surgery with exclusion of the aneurysm. Forty six patients presented subarachnoid hemorrhage due to aneurysmal rupture. By reason of their location, 35 paraclinoid aneurysms (53 %) were superior, 20 medial (30.3 %) and 4 inferior (6 %). Thirty three patients had small aneurysms, 23 large aneurysms, and 10 patients presented giant aneurysms. After surgery, 51 patients had good results, since they scored 4 and 5 in the Glasgow Outcome Score. Three patients presented amaurosis as a surgery-related complication.

Conclusion: Microsurgical management is still the best treatment for these aneurysms, due to its ability to exclude them entirely; besides, is the best method to decompress the optic nerve.

Keywords: Internal carotid artery; Optic nerve; Intracraneal aneurysm; Subarachnoid hemorrhage

Aneurysms of the paraclinoid segment of the intracranial internal carotid artery represent approximately 5 to 11% of all brain aneurysms. Unlike other aneurysms, the anatomy of this region is often more complex and requires special knowledge and skills for treatment. They also have the distinction of being large or giant aneurysms in much higher proportion than other locations.

In this article we review the anatomy and classification of these aneurysms, plus discuss the surgical technique, complications, and results in the treatment of 66 patients with this disease treated at the Hospital de Especialidades of the Centro Médico Nacional Siglo XXI of the Instituto Mexicano del Seguro Social.

Anatomical considerations

From the anatomical point of view, in 1981 Gibo1 and Rothon2 classified the internal carotid into four segments: cervical (C1), petrous (C2), cavernous (C3), and supraclinoid (C4). This classification lacked a transition from the intracavernous carotid to the supraclinoid carotid. Lasjaunias and Santoyo-Vásquez3 described the clinoid segment for the first time in 1984, a fundamental basis for the understanding and development of aneurysms in this region. In 1985, Perneczky3 gave the name to the distal dural ring, which provides the anatomical limit of this segment and is essential for the management of the optical pathway and the internal carotid artery. In 1990 Inoue2 called the segment between the two dural rings the clinoid. In 1996 Bouthillier4 classified the internal carotid artery into seven segments, formally including the clinoid segment in it: cervical (C1), petrosal (C2), lacerum (C3), cavernous (C4), clinoid (C5), ophthalmic (C6), and communicant (C7).

The clinoid segment was defined as the segment of the internal carotid artery that lies between the proximal dural ring and the distal;4-6 by definition, this segment is extradural and is below the anterior clinoid apophysis.

The anterior clinoid apophysis6-9 is a triangular bone protrusion about 1 cm at the base that continues medially to the sphenoid planum and laterally with the lesser wing of the sphenoid. Its base corresponds to the optical pillar, which separates the optical channel from the superior orbital fissure, usually found pneumatized. It is covered with dura, except its lower face, where the carotid-oculomotor membrane is. Understanding its structure is essential for clinoidectomy and clipping these aneurysms.

The ophthalmic segment10 of the carotid starts after the distal dural ring and is a spinal segment. It is the source of two major branches: the ophthalmic artery (originating from dorsal surface of the carotid, so the direction of the dome of these aneurysms is also dorsal, and often contacts the lateral half of the optic nerve) and the superior pituitary artery (ies), which originate from the medial surface of the carotid artery. Therefore the direction of the dome of these aneurysms is also medial. The optic nerve usually moves medially and superiorly.

The carotid cavum, which was described by Kobayashi11,12 in 1989, is a dural recess located on the medial surface of the internal carotid, extending below the distal dural ring. It is in contact with the lateral bone wall of the sphenoid body. This is an aneurysm that is very difficult to access surgically.

Classification of paraclinoid aneurysms

Currently there are many classification schemes for aneurysms of the internal carotid artery that are close to the anterior clinoid apophysis; however, it is clear that these classifications are sometimes confusing and contradictory.11,13-18

Based on our personal experience, the most useful and simplest classification for us, if we take into account the anatomy, surgical findings, and correlation with radiological studies, is Krisht’s classification,11,15,16 which classifies them as paraclinoid aneurysms (Figure 1).

Figure 1 Diagram showing the types of paraclinoid aneurysms. Diagram A shows a side view of the internal carotid artery, showing the upper (dorsal) origin of aneurysms of the ophthalmic artery and the inferior (ventral) origin of paraclinoid aneurysms. The dotted line shows the origin of medial or lateral aneurysms in Diagram B, an anteroposterior view outlining the source of a medial aneurysm (upper pituitary), and the source of a lateral paraclinoid aneurysm (subclinoid).

  •  Superior (ophthalmic artery).
  •  Inferior (ventral).
  •  Lateral (subclinoid).
  •  Medial (superior hypophyseal artery).

Sometimes aneurysms grow so much and have a fusiform arrangement, so it is not possible to determine their place of origin; in these cases they are called global aneurysms.

Clinical manifestations

In addition to the symptom of subarachnoid hemorrhage that can occur when the aneurysm ruptures, these aneurysms are unique in causing visual deficits due to the proximity and compression of the optic nerve. Aneurysms of the ophthalmic artery whose projection is superior (dorsal) to the carotid cause the optic nerve to move superiorly and medially, causing their superolateral surface to be pressed against the falciform ligament, causing inferior and nasal quadrantanopia. In the case of aneurysms of the superior hypophyseal artery, whose projection is medial, these have no direct relationship to the optic nerve, except when large or giant, in which case they cause an elevation of the optic nerve, which causes a bitemporal hemianopia.

On other occasions when these aneurysms are giant, they have been associated with transient ischemic phenomena, because they cause turbulent flow, which can lead to emboli.


In this study we present our surgical experience in the treatment of paraclinoid aneurysms in 66 patients operated on in the period between January 2009 and January 2015 in the neurosurgery department of the Hospital de Especialidades of the Centro Médico Nacional Siglo XXI, of the Instituto Mexicano del Seguro Social.

We use the nomenclature proposed by Bouthillier et al. and focus on paraclinoid aneurysms, i.e., those located in the C5 (clinoid) and C6 (ophthalmic) segments.4

We obtained information on the clinical features, evolution, complications, and outcome of patients by reviewing clinical records. Through reviewing and CT angiography studies we obtained characteristics of the morphology and size of aneurysms, as well as postoperative controls.

Initial management

Patients who presented subarachnoid hemorrhage were admitted to the intensive care unit. Their clinical condition was assessed according to the Hunt and Hess scale. All patients were monitored and the preventive management of the vasospasm was begun.

All patients underwent radiological studies, which consisted of a simple cranial and a CT angiography scan. Also, the degree of subarachnoid hemorrhage was qualified according to the Fisher scale. Patients with hydrocephalus identified were given ventriculostomy.

All patients underwent pan-angiography with digital subtraction, based on which the aneurysms were classified into four types, as described above (Figure 2).

Figure 2 Cerebral angiography of different cases showing in A, superior aneurysms; in B, inferior aneurysms; in C, lateral aneurysms, and in D, medial aneurysms

Patients with paraclinoid aneurysms diagnosed in outpatient, in addition to the radiological studies described above, were sent for campimetric ophthalmologic evaluation.

Surgical technique

Proximal control6,19,20

In this type of paraclinoid aneurysms it becomes very important to obtain proximal control of the afferent vessel. Unlike other aneurysms in other locations, where proximal control can be easily obtained in the afferent intracranial artery, in this segment the presence of bony structures and the cavernous sinus makes proximal vascular control impossible. We prefer to use the cervical carotid artery. After identifying the angle of the jaw, an incision of approximately 3 cm is made at the leading edge of the sternocleidomastoid muscle. It is dissected in depth to expose the bifurcation of the common carotid artery; then the internal carotid artery is identified, dissected, and referred to.

Another option is to gain proximal control at the internal carotid artery in the petrous segment, which has the advantage of not requiring a separate surgical incision; however, there may be risk of auditory complications from cochlear injury, cerebrospinal fluid fistula through the Eustachian tube, and facial injury from elongation of the greater superficial petrosal nerve.21


With the patient supine, with rotation of the head 20 to 30 degrees to the opposite side, with moderate extension of the neck, frontotemporal craniotomy is done centered at the pterion.

The sphenoid ridge is then milled; the intention is to remove most of the lesser sphenoid wing to display the superolateral end of the superior orbital fissure. In some cases resection is indicated in the superior and lateral wall of the orbit, a decision that must be made individually.

Previous clinoidectomy6

This step is very important and the anatomy of the aneurysm must be considered. In aneurysms with medial or ventral projection, clinoidectomy can be completely extradural. However, in the case of dorsal projection aneurysms, especially large or giant, it should be intradural and with direct vision of the aneurysm. This is because excessive "blind" retraction can break the aneurysm. The first step is to open the dura; we hold that in most cases the opening of the Sylvan fissure is not necessary. Having identified the anterior clinoid apophysis, the optic nerve, the internal carotid artery, and, given the case, the aneurysm, we proceed to address the dura that covers the clinoid, making an extension to the sphenoid planum. We begin by deroofing the optical canal with a 2 mm diamond cutter; we then proceed to cut the falciform ligament and the sheath of the lateral optic nerve. We then proceed to milling the clinoid apophysis by cavitation, to medially disinsert the superior and lateral wall of the optical channel and inferiorly disinsert the strut or optical pillar; finally, the eye-motor membrane cortex is inferiorly disinserted. During this removal there may be bleeding from the cavernous sinus, which is easily controlled using surgicel, gelfoam, or intracavernous fibrin adhesive (Tissucol® or Beriplast®).6,11,13

Dissection of dural rings10,13,14

The ophthalmic artery arises just distal to the distal dural ring. After identifying it, we proceed to sever the distal dural ring. This frees the carotid artery in its clinoid segment, so that it can be mobilized and proximal control obtained in case of an aneurysm rupture.

Dissection of the aneurism10,17

The necessity and amount of clinoidectomy and dissection of the distal dural ring should be individualized case by case. On one hand, ophthalmic artery aneurysms, having a dorsal carotid birth and superior projection from the dome, require less distal dural ring dissection. Conversely, superior hypophyseal artery and carotid cavum aneurysms, having medial and inferior projection, require further distal dural ring dissection; this should be virtually the entire circumference of the artery, in addition to the clipping with a fenestrated clip having a blind spot. Sometimes there is a need to medially and superiorly retract the optic nerve, a maneuver to be performed gently. At certain times of the dissection of the neck of the aneurysm we recommend transient occlusion of the proximal carotid artery, to reduce the tension of the aneurysm during dissection.  

Aneurysm clipping

Overall, aneurysms arising from the dorsal carotid can be closed with straight or curved clips that fit the neck of the aneurysm. Care should be taken not to occlude the ophthalmic artery in this clipping. Rather, aneurysms that are born and are projected medially or ventrally require fenestrated clips at right angles. Sometimes, particularly in wide-neck aneurysms that are frequent in this location, it is necessary to place two or more aneurysm clips in "tandem". After clipping, the aneurysm sac is punctured to verify proper occlusion of the aneurysm and decompress the optic nerve.

For global aneurysms, the closure of the internal carotid artery must be both proximal and distal to the site of the aneurysm; the cervical carotid artery is punctured and decompressed (Dallas procedure)6,13,14 and the light of the internal carotid artery is rebuilt with fenestrated clips at a right angle.



We pack the milled margin of bone with bone wax and then make the waterproof closure of the dura as usual. We routinely leave an epidural drain and frequently also subgaleal.


66 patients with the diagnosis of paraclinoid aneurysm were operated on. Of these 65 patients received microsurgical clipping, and one patient underwent a cerebral bypass with exclusion of the aneurysm.

Of the 66 patients 61 were female, which corresponds to 92.4%. The average age was 49.55 years (range 21 to 75 years).

Regarding clinical presentation, in 46 patients this was due to a subarachnoid hemorrhage secondary to a ruptured aneurysm with paraclinoid location; in four patients subarachnoid hemorrhage was presented secondary to a ruptured aneurysm from another location.

In six patients with headache, without subarachnoid hemorrhage, the finding was incidental and was discovered by imaging. In three patients, the aneurysms were manifested by an ipsilateral visual deficit at the site of the aneurysm, which were initially evaluated by Ophthalmology, discovering an aneurysm with compressive effect on the optic nerve. A patient with seizures received imaging studies identifying a left frontoparietal arteriovenous malformation and, incidentally, an aneurysm of the superior ipsilateral hypophyseal artery.

One patient with a right cervical mass, diagnosed with carotid glomus tumor, was given a pan-angiography as part of diagnostic protocol, finding a medial paraclinoid aneurysm.

Multiple aneurysms were found in 28 patients; in 20 cases the paraclinoid aneurysm was the cause of the subarachnoid hemorrhage. In the other eight cases it was another aneurysm that caused the hemorrhage; however, the ruptured aneurysms were treated during surgery. In seven patients aneurysms were found in mirror image, i.e. an aneurysm in the same segment of the internal carotid artery on the contralateral side (Figure 3).

Figure 3 shows a contrasted axial computed tomography (CT) that identifies two saccular dilations in a patient with bilateral upper paraclinoid aneurysms (mirroring). In this case, the largest aneurysm was operated on first

As for the location of aneurysms, the distribution was as follows: superior paraclinoid (true ophthalmic artery) 35 (53%), medial paraclinoid (superior hypophyseal artery) 20 cases (30.3%), and another four cases (6%) were inferior paraclinoid (ventral internal carotid); in one case the aneurysm was global, so classification was not possible.

As for the size of aneurysms, in 33 patients (50%) the aneurysms were small (< 11 mm), in 23 patients (34.8%) the aneurysms were considered large (between 11 and 24 mm), and in 10 cases giant (> 25 mm) (15.15%).

Among surgical complications, one patient of the series (whose aneurysm of the superior hypophyseal artery was incidental) had a transient right brachial monoparesis which improved with rehabilitation. We attribute this to a scheduled transient clipping of the internal carotid artery for four minutes.

One patient had dysarthria-type language impairments, which occurred after surgery; these improved with language rehabilitation.

Three patients had a final ipsilateral amaurosis, an injury that they did not have before surgery. We attribute this complication to manipulation and milling of the optic nerve, as injury from heat and vibration is described.22

In two cases central diabetes insipidus appeared after surgery; in one case it was transient and in the other, permanent.

The remaining complications were related to vasospasm rather than surgery; 13 patients had clinical vasospasm.

In the three cases where patients demonstrated visual field deficits, in one of these, in which the patient developed inferior nasal quadrantanopia, progressive improvement after clipping was verified at four months after surgery, while in the other two cases the deficit persisted unchanged.

In the case of mirror image aneurysms, five of the patients were operated on bilaterally at different times to eliminate their aneurysms. They began on the side of the ruptured aneurysm in three cases, and, in the two cases of unruptured aneurysms, the largest aneurysm was operated on first.

The Glasgow Outcome Score (GOS)23 was used to evaluate the neurological outcome: 1 death, 2 persistent vegetative state, 3 severe disability, 4 moderate disability, 5 minimal or no disability.

36 patients had a good recovery, with GOS of 5 (54.5%); 15 patients (22.7%) had 4; 12 (19%) had 3, and 3 patients (4.5%) had 1 and died from complications of vasospasm and nosocomial pneumonia (Figure 4).

Figure 4 Clinical case: a 43-year-old woman with an incidental aneurysm of the right internal carotid artery. A shows the anteroposterior projection showing a medial paraclinoid aneurysm (upper pituitary artery). B shows the lateral projection. C shows the moment of placement of the fenestrated clip during surgery. D shows the postoperative angiography in lateral projection demonstrating the exclusion of the aneurysm


The natural history of paraclinoid aneurysms is not well known; they have the particularity that they are often large or giant aneurysms, which was confirmed by our series of patients (50%). The anatomical features, for their proximity to the optic nerve, the cavernous sinus, and the anterior clinoid apophysis, make their surgical treatment more technically difficult and impose a neurosurgical challenge to this day. Mastery of the anatomy of this region and proper surgical planning are essential to succeed in this type of aneurysms.

The overall frequency is described in studies worldwide at 5 to 11%; in our neurosurgical service, the approximate rate is 9%, considering all aneurysms operated on.

There are multiple classification schemes, which are sometimes confusing and impractical for proper surgical planning. The importance of correctly classifying the aneurysm is in exactly knowing the segment from the birth of the neck, the projection of the aneurysm, the need for clinoidectomy, the rush to dissect the distal dural ring, and thus choose the clip needed. In each case the chronology and the need for each step should be individualized.

This is demonstrated by the fact that proximal control at the cervical or petroso level is not done in all cases, especially in patients with unruptured and superior paraclinoid aneurysms (arising from the distal dorsal internal carotid artery). Also the need for clinoidectomy is individualized, since the right amount must be resected to make the correct dissection of the aneurysm neck.

Overall, medial and ventral aneurysms are more complex and require more rostral dissection and total clinoidectomy to clip them; in these cases fenestrated clips are used, unlike aneurysms arising from the dorsal portion of the carotid artery, in which straight clips are usually used, and it is sometimes not necessary to dissect and cut the dural ring.

In our series, most patients showed good evolution after surgery, with GOS 4 and 5 in most patients (51 of our 66 patients).

However, three of our patients presented an important functional complication after surgery: permanent amaurosis. This complication is described in surgically treated patients. There are measures to be taken to avoid this complication: special care when unroofing the optical channel, as the dura that covers it must not break, and one must be careful breaking the small pial vessels supplying the optic nerve; also, retraction of the optic nerve should be avoided, and the birth of the ophthalmic artery must be identified.

Endovascular therapy is also described for this type of aneurysm; however, aneurysms in this location also have some unfavorable factors for coil embolization, such as size, wide neck, intra-aneurism thrombi, compression of the optic nerve, and others. In addition, the percentage of recanalization is very high, from 17 to 90%. At present diversion flow stents are used in order to redirect the flow of the afferent artery and decrease the blood flow path within the aneurysm; however, this is not indicated for use in cases of ruptured aneurysms, and the results are preliminary.

Microsurgical management remains the treatment of choice in the management of paraclinoid aneurysms.

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Conflict of interest statement: The authors have completed and submitted the form translated into Spanish for the declaration of potential conflicts of interest of the International Committee of Medical Journal Editors, and none were reported in relation to this article.

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