2026 年 13 巻 p. 317-321
The trigone of the lateral ventricle is surrounded by important white matter fibers, making it difficult to approach. White matter fibers, such as the superior longitudinal fasciculus, optic radiation, arcuate fasciculus, and inferior fronto-occipital fasciculus, can be clearly depicted by tractography. We propose the safest approach to a trigonal tumor of the lateral ventricle via the superior parietal lobe using tractography. Case: A 49-year-old female presented to our hospital with a chronic headache. Magnetic resonance imaging revealed a meningioma with partial hydrocephalus in the trigone of the left lateral ventricle. After total gross resection, the patient exhibited no cranial nerve, visual, sensorimotor, or language deficits. However, there was a mild acalculia right after surgery, from which the patient made an excellent recovery with no neurological deficits at 3 months after surgery. The endoport-assisted superior parietal lobe trans-sulcus approach using tractography is the safest approach to the trigonal lesion, as it protects the most important white matter fibers around the lateral ventricular trigone.
Intraventricular tumors are rare, large tumors typically found in the trigone of the lateral ventricles.1) They usually include meningiomas, ependymomas, or gliomas.2) These tumors grow slowly and are initially asymptomatic but can rapidly lead to life-threatening hydrocephalus and mass effects. Trigonal tumors pose a unique operative challenge in neurosurgery.2) Their deep location within the eloquent area, close proximity to crucial perforating arteries, and being surrounded by important white matter tracts result in technical difficulties. When in the dominant hemisphere, these lesions carry a greater risk of postoperative neurological sequelae.3) However, advances in neurosurgical techniques, planning, and neuronavigation have significantly improved outcomes.1,4) Although multiple approaches to the trigone of the lateral ventricle have been reported,5-8) it is still difficult to completely prevent postoperative neurological deterioration, including higher brain dysfunction. In this report, we propose a less complicated surgical approach via the superior parietal lobe using tractography.
A previously healthy, right-handed, 49-year-old female with chronic headaches presented to our hospital. Gd-enhanced magnetic resonance imaging (MRI) revealed a 24 × 27 × 28 mm3 intraventricular lesion in the left trigone area, causing partial hydrocephalus (Figure 1A-C). The clinical examination was unremarkable, without cranial nerve or focal neurological deficits. Diffusion tensor image with fiber tracking was performed in Elements (Brain LAB AG, Germany) for intraoperative neuronavigation (Figure 1D-F). In the brain surface simulation, the parieto-occipital sulcus (POS) appeared posterior to the lesion, and the intraparietal sulcus (IPS) was observed laterally (Figure 1D). The lesion was bordered posteriorly by the optic radiation (OR) and the inferior fronto-occipital fasciculus (IFOF), and laterally by the superior longitudinal fasciculus (SLF) and the arcuate fasciculus (AF). The precentral and postcentral gyri, along with their descending fibers, were found anteriorly. Considering these important white matter fibers, the most appropriate surgical corridor to avoid damaging these fibers was a sulcus on the median side of the IPS (Figure 1D and E). Postoperative MRI confirmed complete tumor resection (Figure 1G-I), and a pathological exam identified the tumor as a fibrous meningioma. The patient exhibited no cranial nerve, visual, sensorimotor, or language deficits after surgery. Detailed examination revealed a mild acalculia, consistent with a mild, incomplete Gerstmann syndrome. The neuropsychological assessment suggested a good prognosis for functional recovery, recommending a short outpatient rehabilitation cycle. The patient was reassessed at 3 and 6 months postoperatively, making an excellent recovery with no neurological deficits. Lacosamide was administered after surgery until 3 months postoperatively to prevent epilepsy.
Illustrative case of trigone meningioma.
A-C: Preoperative images. MRI FLAIR (A), Gd-enhanced T1 weighted imaging (B), and contrast-enhanced CT (C) revealed a 24 × 27 × 28-mm intraventricular tumor in the left trigone, causing partial hydrocephalus. The posterior choroidal artery running along the tumor is also shown.
D-E: Preoperative 3D simulation images. (D) Brain surface image. (E) Transparent brain depicting the tumor and white matter fibers.
Intraparietal sulcus, yellow line; parieto-occipital sulcus, red line; and direction of approach, white arrow.
F: Preoperative tractography based on diffusion tensor imaging. Green, superior longitudinal fasciculus; red, arcuate fasciculus; blue, optic radiation; and orange, inferior fronto-occipital fasciculus.
G-I: Postoperative images. MRI FLAIR (G), Gd-enhanced T1 weighted imaging (H), and CT (I) showing gross total tumor resection.
3D: 3-dimensional; CT: computed tomography; Gd: gadolinium; MRI FLAIR: magnetic resonance imaging with fluid-attenuated inversion recovery
The institutional review board waives the requirement for approval of single case reports. The patient provided consent for the procedure.
Description of the technique Patient positioning and preparationThe patient was placed in the prone position with slight neck extension (Figure 2A). Then, neuronavigation was prepared. Somatosensory and motor-evoked potentials were monitored according to the tumor extension. Intraoperative visual-evoked potentials were also recorded to assess visual pathway function.
Intraoperative images.
A: The patient was placed in the prone position with slight neck extension.
B: The skin incision was designed to include the central sulcus, POS, and IPS within the craniotomy field.
C: Opening of a sulcus in the superior parietal lobe.
D: Insertion of the endoport.
E: Decompression of the tumor in the trigone.
F: Coagulation of the feeding artery (posterior choroidal artery).
G: Lateral dissection and detachment of the tumor.
H: Tumor removal.
IPS: intraparietal sulcus; POS: parieto-occipital sulcus
The skin incision was designed to include the central sulcus, POS, and IPS in the craniotomy field (Figure 2B). The craniotomy was performed with four burr holes, taking care not to damage the superior sagittal sinus and the dura mater, which was incised in a C-shape with the superior sagittal sinus as a base.
Tumor removalThe first step was opening the targeted brain sulcus (Figure 2C) and setting the Viewsite Brain Access System (Vycor Medical Boca Raton, FL, USA), under a neuronavigation guide, toward the lateral ventricular atrium (Figure 2D). We used Viewsite with a cross-sectional size of 15 × 21 mm and a length of 5 cm. Endoport placement prevented damage to the brain parenchyma during tumor removal (Figure 2E). Since the feeding arteries of trigone meningiomas typically arise from the posterior choroidal artery (Figure 2F) and sometimes from the anterior choroidal artery-located on the deep side of the tumor and cannot be initially identified when entering the lateral ventricle-the tumor must first be debulked and then rolled laterally to medially expose the feeding arteries (Figure 2G). Then, these vessels are coagulated and cut to devascularize and detach the tumor, before rolling the tumor medially to access its anterolateral inferior aspect to coagulate and cut the remaining feeding arteries from the anterior choroidal artery. After detaching the tumor, it was debunked and removed in pieces (Figure 2H).
ClosureNext, the dura mater was closed in a watertight fashion, and a polyglycolic acid seat and fibrin glue were placed on the dura mater to avoid cerebrospinal fluid leak. Thereafter, a bone fragment was fixed to reconstruct the parietal bone with metallic plates, and the periosteum was sutured to cover the metallic plates before closing the subcutaneous tissue and skin.
The video shows the step-by-step surgical procedure (Video).
An appropriate approach for a trigonal tumor in the lateral ventricle should be selected to prevent neurological complications, such as visual field defects and higher brain dysfunction. A variety of surgical approaches have been previously described. In 1976, Kempe and Blaylock recommended a transcallosal approach,7) which may cause a disconnection syndrome with preexisting right homonymous hemianopia,9) and is not suitable for large tumors extending laterally. Transcortical approaches that incise the inferior parietal or posterior temporal lobe often cause motor and speech deficits as well as damage to the OR. A paramedian parieto-occipital route is the most familiar approach for trigonal tumors in the dominant hemisphere.10,11) Even using this approach, postoperative visual field defects, language functions deficits, and higher brain dysfunction can occasionally occur.12) A parieto-occipital interhemispheric precuneus approach for trigonal tumors appears to rarely cause higher brain dysfunction. Nakamura et al. reported a case in which this approach resulted in recent memory disturbances by damaging the fornix.11) Recently, the white matter fiber anatomy has been elucidated,13) facilitating delineation by navigation systems.14) Our surgical approach combines a paramedian parieto-occipital approach with white matter fiber dissection using tractography to maximally reduce postoperative neurologic complications. The white matter fibers to be avoided in this approach are OR, SLF, IFOF, and AF. Disorders of the visual field are caused by disturbances in the OR. SLF is related to language functions in the dominant hemisphere and to spatial awareness by integrating visuospatial and audiospatial information in the nondominant hemisphere.14) The IFOF, localized just below the SLF, plays a significant role in non-articulatory functions of language such as syntax and grammar.14) Language impairment after the conventional paramedian parieto-occipital approach is thought to be caused by damage to the SLF ventral rami. AF connects the fronto-opercular cortical sites with the posterior temporal cortex. It is a white matter tract connecting the canonical Broca's and Wernicke's areas.15)
The trans-sulcus approach minimizes white matter damage, which may help prevent symptomatic epilepsy after surgery.16)
Endoscopic surgery using an endoport is also being considered. In terms of observing the surgical field, endoscopic surgery is like microsurgery. However, because the endoscope remains inside the endoport during the resection procedure, surgical manipulation is more restricted compared to that in microsurgery. Even under a microscope, the narrow surgical corridor for tumor removal is limited within the endoport. Large tumors may need more time to be removed. Later, devascularization of the feeding artery may also be the cause of increased bleeding during tumor removal. In such cases, preoperative embolization should be aggressively considered.
ConclusionsThe endoport-assisted superior parietal lobe trans-sulcus approach using tractography is the safest approach to a trigonal lesion as it protects the important white matter fibers around the lateral ventricular trigone.
All authors have no conflict of interest.
The informed consent was obtained from the patient.
