CASE REPORT
Isolated Abducens Nerve Palsy Caused by a Meningohypophyseal Trunk Aneurysm Treated with Endovascular Coiling: A Case Report
2026 年 13 巻 p. 85-90
詳細
2026 年 13 巻 p. 85-90
Aneurysms of the meningohypophyseal trunk are rare and usually asymptomatic, but because of the close anatomical relationship between the meningohypophyseal trunk and cranial nerves within the cavernous sinus, they can cause neurological deficits. We describe an 80-year-old woman who presented with acute horizontal diplopia exacerbated on rightward gaze. Neurological examination revealed isolated right abducens nerve palsy. Magnetic resonance angiography demonstrated an aneurysm arising from the right meningohypophyseal trunk in close proximity to the abducens nerve. Endovascular coil embolization was performed under dual antiplatelet therapy, and the aneurysm was successfully occluded while preserving meningohypophyseal trunk patency. The procedure was uneventful, although postoperative diffusion-weighted imaging revealed multiple small cerebral infarctions suggestive of distal embolism. The patient remained neurologically stable, and her diplopia gradually improved. At the 6-month follow-up, she exhibited complete recovery of abducens nerve function. This case highlights the anatomical vulnerability of the abducens nerve to compression by meningohypophyseal trunk aneurysms and underscores the importance of considering vascular lesions in the differential diagnosis of isolated cranial nerve palsies. Despite radiographic evidence of silent embolic infarction, endovascular coil embolization resulted in full clinical recovery, supporting its role as a safe and effective therapeutic option in appropriately selected symptomatic meningohypophyseal trunk aneurysms.
The meningohypophyseal trunk (MHT) arises from the cavernous segment of the internal carotid artery (ICA) and typically trifurcates into the tentorial artery (also known as the medial tentorial artery of Bernasconi-Cassinari), the inferior hypophyseal artery, and the dorsal meningeal artery.1-3) It supplies adjacent neural and dural structures, including cranial nerves III, IV, V, and VI, as well as the posterior pituitary gland.2,4) Aneurysms arising from the MHT are rare and often asymptomatic due to their small size and deep location. However, because of the close proximity of the MHT to the abducens nerve in Dorello's canal, MHT aneurysms may cause isolated abducens nerve palsy.5) We report a rare case of isolated right abducens nerve palsy caused by a large MHT aneurysm, which was treated with endovascular coiling. This case highlights both the anatomical vulnerability of the abducens nerve and the feasibility of endovascular intervention in this challenging vascular territory.
An 80-year-old woman presented with sudden-onset horizontal diplopia, exacerbated by right gaze. Neurological examination revealed isolated right abducens nerve palsy. Her medical history included thyroid cyst resection and treatment with levothyroxine and eldecalcitol. Magnetic resonance angiography (MRA) revealed an aneurysm arising from the C4 segment of the right ICA (Figure 1A and B). Heavy T2 image showed contact between the aneurysm and the right abducens nerve around Dorello's canal (Figure 1C and D). Source and three-dimensional images of computed tomography angiography and digital subtraction angiography (DSA) confirmed an MHT aneurysm (Supplementary Figures 1 and 2 and Figure 2A-D). Given the abducens nerve palsy due to the aneurysm and branching of MHT from the aneurysm dome, endovascular coiling was pursued. She was on dual antiplatelet therapy (aspirin and clopidogrel).
3D time-of-flight image of brain MRA and Heavy T2-weighted images at the pontine level on admission.
Anterior-posterior view (A) and oblique view of MRA (B) indicate an aneurysm (asterisk) arising from the C4 segment of the right internal carotid artery. Axial MR images showing the right abducens nerve (black arrowheads) (C and D) in close proximity to the aneurysm (asterisks). The aneurysm is seen displacing or compressing the nerve at the level of Dorello’s canal.
3D: 3-dimensional; MR: magnetic resonance; MRA: magnetic resonance angiography
Preoperative DSA.
Right internal carotid angiography (A, anteroposterior view; B, lateral view) demonstrates a large aneurysm arising from the meningohypophyseal trunk (black arrowheads). 3D rotational angiogram demonstrated an aneurysm arising from the meningohypophyseal trunk, with branching consistent with the tentorial artery (C). Aneurysm width, height, and neck are 16.0 mm, 10.7 mm, and 5.1 mm, respectively (D).
3D: 3-dimensional; DSA: digital subtraction angiography
Under general anesthesia, a 7 Fr guiding sheath was placed into the right ICA. An AXS Vecta 71 intermediate catheter (Stryker, Kalamazoo, MI, USA) was used to navigate an Excelsior SL-10 STR microcatheter (Stryker) to the C4 segment of the right ICA. Th microcatheter was inserted into the aneurysm and the aneurysm, was embolized using the following 15 coils: Target Standard (Stryker): 20 mm× 50 cm, 18 mm× 50 cm, 16 mm× 50 cm (×2), 14 mm× 50 cm, Axium Prime Frame Complex (Medtronic, Minneapolis, MN, USA): 12 mm× 50 cm, Target XL360 Soft (Stryker): 10 mm× 40 cm, iED Complex SS (Kaneka Medix Corporation, Osaka, Japan): 3-5 mm× 20 cm (×2), Axium Prime Frame 3-dimensional (3D) (Medtronic): 8 mm× 30 cm, Axium Prime Bare Platinum (Medtronic): 4 mm× 12 cm (×2), 3.5 mm× 8 cm, 3 mm× 6 cm, Target Tetra (Stryker): 3 mm× 6 cm. After sufficient embolization was achieved, the patency of MHT was confirmed (Figure 3A and B).
DSA immediately after and 6 months following coil embolization.
Anteroposterior (A) and lateral (B) views of DSA show complete obliteration of the aneurysmal sac and the patency of the meningohypophyseal trunk (black arrowhead). Anteroposterior (C) and lateral (D) views of DSA show aneurysm neck remnant and the patency of the meningohypophyseal trunk (Black arrowhead).
DSA: digital subtraction angiography
Postoperative diffusion-weighted imaging demonstrated multiple spotty high-intensity lesions in the cerebral hemispheres (Supplementary Figure 3), suggestive of small embolic infarctions. However, the patient remained neurologically stable, and no new deficits developed as a result of these infarctions. Her diplopia gradually resolved, and complete recovery of abducens nerve function was confirmed at 6-month follow-up. Follow-up DSA (Figure 3C and D) and MRA (Figure 4A and B) were performed at 6 months and 1.5 years after the embolization. Partial recanalization was confirmed, and the patient continued follow-up at the outpatient clinic in our hospital.
3D time-of-flight image of brain MRA 1.5 years after coil embolization.
Anterior-posterior view (A) and oblique view of MRA (B) indicate an aneurysm neck remnant (white arrowhead).
3D: 3-dimensional; MRA: magnetic resonance angiography
Written informed consent was obtained from the patients.
Although aneurysms of the MHT are rare, their clinical relevance lies in their potential to compress adjacent cranial nerves within the cavernous sinus. Among these, the abducens nerve is particularly vulnerable due to its long intracranial course and fixed trajectory through Dorello's canal. It arises at the pontomedullary junction and travels through the subarachnoid space and the cavernous sinus before entering the orbit via the superior orbital fissure. Within the cavernous sinus, the nerve courses medially along the ICA and derives part of its blood supply from the dorsal meningeal artery, a branch of the MHT.6) The anatomical proximity between the MHT and the abducens nerve has been demonstrated in cadaveric studies. Jittapiromsak et al.5) reported that in cases with a normally curved ICA, the MHT lies approximately 5.5 mm from the abducens nerve, whereas in redundant ICA configurations, the distance increases to 10.0 mm. These findings underscore how even subtle anatomical variations may influence the likelihood and mechanism of nerve compression. As noted in our case, aneurysms in this region can lead to isolated abducens nerve palsy either by direct compression or by ischemic insult resulting from compromised microvascular perfusion.
Our patient presented with classic signs of isolated abducens nerve palsy. In elderly individuals, this condition often raises suspicion of microvascular ischemia related to diabetes or hypertension. However, the absence of such risk factors in this case, along with the identification of an MHT aneurysm on MRA, shifted the diagnostic focus. Notably, heavy T2-weighted imaging revealed direct contact between the aneurysm and the abducens nerve, further supporting a compressive etiology. This case highlights the value of high-resolution MR imaging in visualizing neurovascular relationships and informing diagnostic decisions.
While most MHT aneurysms are incidentally detected and may be managed conservatively, symptomatic aneurysms-particularly those associated with progressive cranial nerve deficits-require treatment. In our case, endovascular coil embolization was chosen due to the deep and surgically inaccessible location of the aneurysm. This treatment strategy aligns with recent evidence showing that endovascular approaches achieve the highest cranial nerve recovery rate (approximately 93%), clearly outperforming conservative management (28%) and slightly exceeding microsurgical outcomes (80%).7) Because the MHT originated directly from the aneurysmal dome, special attention was paid to preserving its patency during coiling, as occlusion of the MHT can result in pituitary dysfunction, including diabetes insipidus.4) The use of soft, shape-conforming coils facilitated secure packing of the aneurysm while minimizing the risk of compromising adjacent perforators or the parent artery. While flow diverter placement could be an alternative option for ICA-cavernous aneurysms incorporating the MHT or tentorial branch, we opted for selective coiling to preserve the MHT and minimize the risk of pituitary ischemia. Postoperative diffusion-weighted imaging revealed multiple spotty high-intensity lesions in the cerebral hemispheres, suggestive of distal embolic infarctions. Fortunately, these were clinically silent, and the patient experienced no new neurological deficits. Her complete recovery underscores the feasibility and safety of endovascular treatment in appropriately selected cases, provided that meticulous technique and careful device selection are employed. Another important differential diagnosis is a lateral-type persistent primitive trigeminal artery variant.8) In such cases, the aneurysm may arise at the bifurcation where the persistent primitive trigeminal artery connects with the basilar artery or its branches, such as the anterior inferior cerebellar artery or posterior inferior cerebellar artery. In our case, however, careful review of the 3D rotational angiography demonstrated that the branching vessel from the aneurysmal dome coursed toward the tentorium and was continuous with the tentorial artery, consistent with the MHT. No direct communication with the vertebrobasilar system was identified. These angiographic features strongly supported the diagnosis of an MHT aneurysm rather than a persistent primitive trigeminal artery variant.
To our knowledge, this is the first report describing the successful endovascular coiling of an MHT aneurysm causing isolated abducens nerve palsy. Most previously reported cases of aneurysms affecting the abducens nerve have involved the cavernous segment of the ICA itself.9) This case contributes to the literature by documenting a rare but anatomically and clinically plausible cause of sixth nerve palsy and by providing both radiological and clinical evidence supporting the MHT aneurysm as the causative lesion.
Long-term imaging follow-up in our patient revealed partial recanalization, a known phenomenon in aneurysms treated with coil embolization. However, no recurrence of neurological symptoms was observed, and the patient continues to be monitored in the outpatient setting. This case underscores the importance of both radiological surveillance and clinical follow-up in the long-term management of complex aneurysms involving critical neurovascular structures. Minor recanalization was observed during follow-up, which may have been partly related to intentional preservation of the MHT. While preservation is important to avoid pituitary dysfunction, it is known that incomplete embolization of the aneurysm neck-including the MHT orifice-may predispose to recanalization. In other contexts, balloon occlusion testing of the ICA has been shown to be a useful preoperative tool for assessing collateral cerebral perfusion efficacy.10,11) Although not specifically validated for the MHT territory, such an approach could potentially guide decision-making regarding whether to include the MHT orifice in the embolization by evaluating whether collateral supply is sufficient.
ConclusionsWe report a rare case of isolated abducens nerve palsy caused by an aneurysm of the MHT. Despite the presence of small, clinically silent cerebral infarctions following treatment, endovascular coiling resulted in complete neurological recovery. This case highlights the importance of considering vascular etiologies in patients with isolated cranial nerve palsies and supports the role of endovascular intervention in anatomically challenging lesions.
Author Nobuyuki Sakai is one of the Editorial Board members of the Journal. This author was not involved in the peer-review or decision-making process for this paper.
We sincerely thank Mr. Kunio Hamaya, radiological technologist, for his expert assistance in generating the three-dimensional computed tomography angiography reconstructions used in Supplementary Figure 2.
Fuminori Shimizu: Writing - original draft, Investigation. Hidetoshi Matsukawa: Writing - original draft, Investigation. Yusuke Kitada: Writing - review & editing. Hiroto Kakita: Writing - review & editing. Nobuyuki Sakai: Writing - review & editing.
HM received a lecture fee from Daiichi-Sankyo and Stryker and a consulting services fee from B. Braun. NS received a research grant from Century Medical, Japan Lifeline, Kaneka, Medtronic, Penumbra, Terumo, and TG Medical; lecture fees from Asahi-Intech, Kaneka, Medtronic, SB Kawasumi, Stryker, and Terumo; membership on the advisory boards for Johnson&Johnson MedTech, Medtronic, and Terumo outside the submitted work.
