BACKGROUND: Managing lesions situated in the atrium of the lateral ventricle remains a challenging neurosurgical problem. The purposes of this study were to examine the microsurgical anatomy of the atrium of the lateral ventricle and the optic radiation and to define the differences in the exposure obtained by various surgical approaches.

METHODS: Fifteen adult cadaveric specimens were studied using magnification 3 to 40 after perfusion of the arteries and veins with colored silicone. The microsurgical anatomy of the atrium of the lateral ventricle was examined. The relationship between the optic radiation and the atrium was studied using the white matter fiber dissection technique. Surgical approaches to the atrium of the lateral ventricle were examined in stepwise dissection.

RESULTS: The medial and inferior walls of the atrium were free from optic radiation fibers. Surgical approaches to the atrium of the lateral ventricle are divided into 3 routes: (1) anterior approach: transsylvian approach, (2) posterior approaches: posterior transcortical, posterior transcallosal, occipital, and supracerebellar transtentorial approaches, and (3) lateral approaches: transtemporal and subtemporal approaches.

CONCLUSION: Knowledge of the microsurgical anatomy of the atrium of the lateral ventricle and surrounding vital structures and the choice of an appropriate surgical approach will help surgeons perform safe and minimally invasive surgery.

Direct surgical approaches to the atrium of the lateral ventricle remain a challenge because of their deep location, the important neural structures in the area, and their relationship to the choroidal arteries and deep venous system. The atrium of the lateral ventricle is not an uncommon site of neoplastic and vascular lesions that may be approached anteriorly, posteriorly, laterally, or inferiorly [2-6,9,10,12-14,18,26].

The purposes of this study were, first, to examine the microsurgical anatomy of the atrium of the lateral ventricle and the relationship between the atrium and the optic radiation and, second, to define various surgical approaches to the atrium.

The exposure obtained with approaches to the atrium of the lateral ventricle and related anatomy were examined in stepwise dissections using 15 adult cadaveric specimens and magnification ×3 to ×40. The relationship between the optic radiation and the atrium was examined using the white matter fiber dissection technique. The arteries and veins were perfused with colored silicone. The bone dissections were performed with a Midas Rex drill (Fort Worth, Tex).

Atrium of the lateral ventricle. The atrium of the lateral ventricle opens anteriorly above the thalamus into the body of the lateral ventricle, anteriorly below the thalamus into the temporal horn, and posteriorly into the occipital horn. The roof of the atrium is formed by the body, splenium, and tapetum of the corpus callosum. The floor is formed by the collateral trigone, which overlies the collateral sulcus. The inferior part of the medial wall is formed by the calcar avis, the prominence that overlies the deep end of the calcarine sulcus. The superior part of the medial wall is formed by the bulb of the corpus callosum, which overlies the forceps major. The lateral wall has an anterior part, formed by the caudate nucleus, and a posterior part, formed by the tapetum. In the atrium, the choroid plexus has a prominent tuft called the glomus (Fig. 1A-D).

Optic radiation. Some fibers of the internal capsule curve around the posterior edge of the lentiform nucleus and are referred to as the retrolenticular fibers, and other fibers pass below the lentiform nucleus and are referred to as sublenticular fibers. The sublenticular part of the posterior limb contains the auditory radiation fibers directed from the medial geniculate body to the auditory area in the transverse temporal and adjacent parts of the superior temporal gyri and part of the optic radiations that course from the lateral geniculate to the walls of the calcarine sulcus. Some optic radiation fibers also pass through the retrolenticular part of the internal capsule, but most pass through the sublenticular part (Fig. 2A and B).

The optic radiations are separated from the roof and lateral wall of the temporal horn and the lateral atrial wall by a thin layer of tapetal fibers. The fibers passing to the superior bank of the calcarine fissure leave the upper part of the lateral geniculate body and course almost directly posterior around the lateral aspect of the atrium of the lateral ventricle to reach the striate visual cortex. Fibers from the lower part of the geniculate body destined for the inferior bank of the calcarine fissure initially loop forward and downward in the temporal lobe, forming Mayer’s loop, before turning back to join the other fibers in the optic radiations.

The fibers of the optic radiation are divided into anterior, middle, and posterior groups. The anterior loop along fibers, called Mayer’s loop, subserve the upper half of the visual field. They initially take an anterior direction above the roof of the temporal horn, usually reaching as far anteriorly as the tip of the temporal horn, where they loop along the lateral and inferior aspects of the atrium and occipital horn to reach the lower lip of the calcarine fissure. The middle fibers, subserving the macula, course laterally above the roof of the temporal horn and turn posteriorly along the lateral wall of the atrium and occipital horn. The posterior fibers responsible for the lower visual field course directly backward along the lateral wall of the atrium and occipital horn to end in the upper lip of the calcarine fissure (Fig. 2C and D).

Choroidal arteries. The arteries most intimately related to the atrium of the lateral ventricle are the choroidal arteries that supply the choroid plexus in the atrium and temporal horn. They arise from the internal carotid and posterior cerebral arteries in the basal cisterns and reach the choroid plexus by passing the choroidal fissure.

The choroid plexus of the atrium is supplied by the anterior and lateral posterior choroidal arteries. Each of the choroidal arteries gives off branches to the neural structures along its course. The anterior choroidal artery arises from the internal carotid artery and courses posteriorly to reach the middle incisural space, where it passes through the choroidal fissure near the inferior choroidal point. It passes posteriorly and dorsally along the plexus, reaching the foramen of Monro in a few hemispheres (Fig. 3A). The lateral posterior choroidal arteries are a group that arises in the ambient and quadrigeminal cisterns from the posterior cerebral artery or its cortical branches. These branches enter the ventricle behind the branches of the anterior choroidal artery. They pass laterally around the pulvinar and through the choroidal fissure at the level of the fimbria, crus, and body of the fornix to reach the choroid plexus in the temporal horn, atrium, and body. There are frequent anastomoses between the branches of the anterior and lateral posterior choroidal arteries on the surface of the choroid plexus.

Ventricular veins. The ventricular veins are divided into medial and lateral groups based on whether they course through the thalamic or the forniceal side of the choroidal fissure. The lateral group passes through the thalamic or inner side of the fissure, and the medial group passes through the outer or forniceal circumference of the fissure. Both groups course along the walls of the ventricle in a subependymal location toward the choroidal fissure.

The medial group of veins in the atrium of the lateral ventricle consists of medial atrial veins, and the lateral group is composed of the lateral atrial veins. The medial atrial veins drain forward on the medial wall of the atrium toward the choroidal fissure. They may also drain the adjacent part of the roof or floor. They pass through the choroidal fissure or the crus of the fornix and terminate within the velum interpositum or quadrigeminal cistern in the internal cerebral or basal veins or their tributaries. The lateral atrial veins drain the anterior and lateral walls of the atrium and the adjacent part of the roof and floor (Fig. 3B and C). They join the internal cerebral, basal, or great vein. The medial and lateral atrial veins may join near the choroidal fissure to form a common trunk called the common atrial vein.

The operative approaches to the atrium of the lateral ventricle are divided into anterior, posterior, and lateral approaches (Fig. 4).

Distal sylvian approach. The distal sylvian approach may be selected for the removal of small lesions in the atrium of the lateral ventricle. After wide exposure of the frontotemporoparietal lobes, the sylvian fissure is widely opened to identify the transverse gyrus of Heschl, which is an orienting landmark for the atrium, on the superior surface of the temporal lobe. The medial end of the transverse gyrus of Heschl corresponds to the posterior end of the insular cortex. The longitudinal axis corresponds to the access to the atrium through the posterior end of the insular cortex (Fig. 5A and B).

Posterior transcortical approach. The posterior transcortical approach exposes the interior of the atrium of the lateral ventricle and the posterior part of the body of the lateral ventricle. The cortex is incised in the long axis of the superior parietal lobule in the region behind the postcentral sulcus. This cortical incision avoids the visual pathway traversing the parietal lobe and the speech area at the junction of the parietal and temporal lobes. The lateral ventricle is entered above the junction of the body and atrium. The choroid plexus provides an orientating landmark. This approach exposes the calcar avis and bulb of the corpus callosum in the medial wall, pulvinar in the anterior wall, and the collateral trigone in the floor (Fig. 6A and B).

The lower part of the atrium may also be approached through cortical incisions in the temporoparietal junction. Exposing the atrium through this route may cause a homonymous visual field deficit because of the interruption of the optic radiation in either hemisphere, disturbance of visuospatial function in the nondominant hemisphere, and aphasia and agnostic disorders in the dominant hemisphere.

Posterior transcallosal approach. The posterior transcallosal approach is best suited to lesions that extend upward from the atrium of the lateral ventricle or third ventricle through the posterior part of the splenium or that arise in the splenium and extend into the atrium and third ventricle. The operation is commonly performed in the three-quarter prone position. After parieto-occipital craniotomy, the dura is reflected toward the sagittal sinus. Opening the arachnoid below falx exposes the distal branches of the anterior cerebral arteries and occasionally the splenial branches of the posterior cerebral arteries on the surface of the corpus callosum. The junction of the internal cerebral veins with the great veins comes into view below the splenium and above the pineal gland. The posterior part of the corpus callosum is incised in the midline. This callosal incision opens the lateral ventricle, which deviates laterally at this point. The opening through the lateral part of the splenium into the atrium exposes the crus of the fornix, bulb of the corpus callosum, pulvinar, and choroid plexus (Fig. 6C and D).

Occipital approach (interhemispheric transprecuneus approach). The occipital approach is suitable for tumors that are situated in the pineal region and the part of the pulvinar, medial occipital lobe, and medial wall of the atrium of the lateral ventricle facing the quadrigeminal cistern. The patient is positioned in a three-quarter prone position with the occipital area to be operated lowermost and the face turned toward the floor. This allows the medial occipital surface along which the approach is directed to relax away from the falx, thus reducing the need for brain retraction [1]. A tumor in the atrium that extends into the medial occipital cortex, near the junction of the vein of Galen and straight sinus, can be exposed from this approach by opening through the precuneus in front of the parietooccipital sulcus. The opening enters the medial wall of the atrium behind the choroidal fissure. The lateral posterior choroidal arteries pass through the choroidal fissure in this area, and the medial posterior choroidal arteries and basal vein can be seen beside the pineal gland. The quadrigeminal plate, trochlear nerve, superior cerebellar artery, and precentral cerebellar vein may be seen in the depth of the exposure (Fig. 6C and D).

Supracerebellar transtentorial approach. Proceeding upward along the undersurface of the tentorium, over the cerebellar hemisphere, leads to the ambient cistern where the floor is the middle cerebellar peduncle and the medial wall is the midbrain. Then, the tentorium is cut from below, beginning around the midportion and extending as posteriorly as possible in the direction of the posterior margin of the tentorial hiatus. The free cut edge of the tentorium is then retracted, together with the superior surface of the cerebellum. Compared with the median and paramedian infratentorial supracerebellar approaches, the advantage of this approach is visualization of the posterior inferior surface of the temporal lobe. This approach provides access to the inferior part of atrium of the lateral ventricle and posterior part of the hippocampus by sectioning the occipitotemporal gyrus, or collateral sulcus, on the inferior surface of the temporal lobe (Fig. 6E and F).

The lateral approaches to the atrium of the lateral ventricle are directed through the lower part of the lateral hemispheric surface or below the lateral hemispheric border.

Transtemporal approach. A temporal craniotomy and a transtemporal cortical incision are used for a lesion in the middle or posterior third of the temporal horn and the atrium of the lateral ventricle. For the temporal craniotomy centered above the ear, the patient is positioned in a supine position with the shoulder on the side of the lesion elevated and the head tilted 60⁰ to 80⁰ away from the side of the operation. The scalp incision extends from above the zygoma anterior to the ear to the area above the ear and then posteriorly and downward to the region of the asterion posterior to the ear. The scalp, temporalis muscle and fascia, and pericranium are reflected as a single layer. The bone flap is cut low, or a small craniectomy below the flap is carried down to the floor of the fossa. This may open the mastoid air cells. Care should be taken not to open the attic of the middle ear. Transient deafness from effusion of fluid into the middle ear may follow this approach. The temporal horn and atrium of the nondominant hemisphere may be exposed using a cortical incision in the middle or inferior temporal gyrus (Fig. 7A).

Subtemporal approach. An alternative and often preferable route, which minimizes the possibility of damage to the optic radiations and speech centers of the dominant hemisphere, is the subtemporal route, in which an incision is made in the inferior temporal or occipitotemporal gyrus or the collateral sulcus on the lower surface of the temporal lobe. The risk of hemorrhage, venous infarction, and edema after retraction of the temporal lobe is reduced by avoiding occlusion of the bridging veins, especially the vein of Labbé (Fig. 7B and C).

Neoplastic and vascular lesions involving the atrium of the lateral ventricle are not rare [2,3,5,13,14]. The technical challenges presented by these lesions and their variable relationship to the atrium have resulted in the development of various operative approaches, each with specific advantages and disadvantages. Some controversy exists regarding the appropriate approach to lesions in this region [2,3,14]. The selection of the best operative approach for a lesion in the atrium depends on the site of origin, path of growth, vascular relationship, location of the tumor, and whether there is ventricular obstruction.

To proceed with surgical exposures to the medial structures of the temporal lobe and exposure of the atrium, a knowledge of the relationship between the optic radiations and the atrium and superficial anatomy of the temporal lobe is required. A useful technique for demonstrating the white matter tracts of the brain is the fiber dissection technique [20,21]. Several authors have reported the 3-dimensional anatomy of the optic radiations using this technique [15,17,24]. Based on the results of these prior studies and the present study, the optic radiation covers the entire lateral aspect of the temporal horn and atrium as it extends to the occipital horn. Anterior, inferior, and posteroinferior routes to the atrium would avoid the optic radiations.

The distal sylvian approach may be selected for the removal of small lesions in the atrium of the lateral ventricle [12]. An advantage of this approach to the atrium is that the wide operative field is available by opening the sylvian fissure. In addition, the transverse gyrus of Heschl is an orienting landmark for the atrium on the superior surface of the temporal lobe. A disadvantage of the approach, especially if it is directed over the dominant hemisphere, is that the optic radiations and hearing centers may be damaged. The posterior transcortical approach directed through the superior parietal lobule is the preferred route for exposing lesions situated within the posterior part of the body and the atrium of the lateral ventricle or arising in the glomus of the choroid plexus [4,5,14]. It may also be selected for a tumor involving the posterior third ventricle if it extends into the posterior thalamic surface facing the atrium and quadrigeminal cistern. However, the posterior transcortical approach through the atrium does not provide satisfactory exposure of the typical midline pineal tumor. The posterior parietal route theoretically avoids damage to the visual and speech areas. The disadvantages of this approach are a long surgical distance and difficult access to the vascular pedicle of the tumor. The transcortical-transventricular exposures are more difficult to perform if the ventricles are not dilated. Selected lesions within the atrium of the lateral ventricle may be exposed by the posterior transcallosal or the occipital interhemispheric approaches. The posterior transcallosal approach directed along the medial occipital surface may be selected for a lesion that extends upward from the atrium through the posterior part of the splenium, or that arises in the splenium and extends into the roof or the upper part of the medial wall of the atrium, or that arises in the splenium and extends into the posterior third ventricle [7,9]. The transcallosal approach has many theoretical advantages, including low incidence of postoperative seizure, no complication of speech and visual functions, and expeditious access to the posterior choroidal artery. Kempe and Blaylock [9] first reported excellent results in 3 patients with small tumors in the left atrium of the lateral ventricle, using this approach. However, the series of Kempe and Blaylock included a patient with right homonymous hemianopsia, which has been considered a contraindication to this approach because a severely disabling syndrome of visual-verbal disconnection can result [11]. Tumors in the posterior part of the third ventricle are usually approached by the occipital transtentorial or infratentorial supracerebellar approaches, but they may also be reached through the posterior part of the lateral ventricle or corpus callosum if they also involve the medial wall of the atrium or corpus callosum. The occipital transtentorial approach is preferred for tumors centered at or above the tentorial edge if there is not a major extension of tumor to the opposite side or into the posterior fossa and for those located above the vein of Galen [1,8,16,19]. A lesion in the atrium of the lateral ventricle that extends into the medial occipital cortex, near the junction of the vein of Galen and straight sinus, can be exposed from interhemispheric transprecuneus approach by opening through the precuneus in front of the parieto-occipital fissure [18,25]. The opening enters the medial wall of the atrium behind the choroidal fissure. The advantages of this approach are a low incidence of visual dysfunction, wide exposure of the atrium, and easy access to the choroidal arteries. The infratentorial supracerebellar approach is best suited to tumors in the midline below the vein of Galen that grow into both the posterior part of the third ventricle and the posterior fossa, displacing the quadrigeminal plate and the anterosuperior part of the cerebellum. The infratentorial supracerebellar approach is, however, not well suited to the tumor with a significant extension above the tentorium or growing from the atrium or corpus callosum into the third ventricle. The supracerebellar transtentorial approach was first described by Voigt and Yaşargil [23] in 1976. Compared with the median and paramedian infratentorial supracerebellar approaches, the advantage of the supracerebellar transtentorial approach is visualization of the posterior inferior surface of the temporal lobe [8,16]. In addition, this approach provides access to the inferior part of atrium and posterior part of the hippocampus by sectioning the fusiform gyrus. Yonekawa et al [26] reported on a series of 16 patients who underwent surgery via the supracerebellar transtentorial approach. The authors demonstrated that this approach could provide easy access to the posterior temporomedial region for removal of tumors, clipping of aneurysms, and performing an amygdalohippocampectomy. The temporal horn and atrium may be approached by the transtemporal or subtemporal approach [2,3,13]. The temporal and subtemporal routes to the temporal horn and atrium are used for a lesion in the posterior third of the temporal horn and anteroinferior part of the atrium, or for selected lesions in the cisterns medial to the temporal horn. In the direct transtemporal approach, the atrium is exposed by an incision in the middle or inferior temporal gyrus on the optic radiations. A preferable route is the subtemporal route, which minimizes the possibility of damage to the optic radiations and speech centers of the dominant hemisphere [10]. In the subtemporal approach, the cortical incision is in the occipitotemporal (fusiform) gyrus, occipitotemporal sulcus, or collateral sulcus, on the inferior surface of the temporal lobe. The opening into the temporal horn will expose the choroidal fissure. Opening through the choroidal fissure in the temporal horn by incising the tenia fornix will provide transventricular access to the area along the posterior cerebral artery and basal vein in the ambient cistern [6,22].

In conclusion, precise anatomical knowledge is required to manage lesions in the atrium of the lateral ventricle. The optic radiation is an especially important structure affecting surgical outcome. Based on these anatomical considerations, the selection of an appropriate surgical approach to the atrium of the lateral ventricle should depend on the location and extent of the tumor or vascular lesion and partly on the surgeon’s experience.

Contributors: Masatou Kawashima, MD, Xiaoyong Li, MD, Albert L. Rhoton, Jr, MD, Arthur J. Ulm, MD, Hidehiro Ok, MD, and Kiyotaka Fujii, MD

Content from Kawashima M, Li X, Rhoton AL, Jr, Ulm AJ, Oka H, Fujii K. Surgical approaches to the atrium of the lateral ventricle: microsurgical anatomy. Surg Neurol 2006;65:436–445. doi.org/10.1016/j.surneu.2005.09.033.

The Neurosurgical Atlas is honored to maintain the legacy of Albert L. Rhoton, Jr, MD.