Ocular motor CNs III, IV, and VI supply motor fibers to the extraocular eye muscles . Although CMs of the ocular motor CNs are extremely rare, these lesions result in stable or progressive isolated CN deficits, such as diplopia and strabismus [1, 3, 22]. Because CMs are occult vascular lesions, some patients develop subarachnoid hemorrhage (SAH), although they are not as severe as an aneurysmal SAH [23, 26]. In our study, there was no disease-related mortality; however, all patients experienced diplopia and strabismus, which impaired their quality of life. Therefore, functional preservation is vital in the surgical management of patients with CMs involving the ocular motor CNs. Surgical resection without any postoperative neurological deficit for treating patients with CMs is debatable, and other factors such as clinical presentation, degree of CM adhesion to the CNs, and history of bleeding should be considered [1, 10]. However, this study focused on the surgical methodology based on its ability to preserve and/or improve CN function.
Presently, CMs are easily detected with gradient-echo and T2-susceptibility weighted MRI sequences [1, 2, 11]. Treatment of CM involving the ocular motor CNs is based on MRI findings. For cases with suspicious MRI findings and progressive, isolated CN deficits, the physician must perform prompt surgical treatment. In our study, some patients, including our patient, were promptly treated with CM resection and preservation of nerve continuity, and they showed recovery of the CN function [2, 12, 15, 22].
Previously, GTR and nerve transection were owing to the risk of re-bleeding from the remnant lesion, and assuming that patients with complete CN palsy did not have the possibility of recovery [16, 19, 24]. Scott et al. regretted their decision to transect the nerve for removing CMs . In our review, all patients who underwent nerve transection experienced complete CN palsy postoperatively, and had persistent diplopia, strabismus, and/or ptosis [3, 14, 16, 19, 24]. GTR and end-to-end anastomosis were performed only for cases of CMs of CN IV [6, 11, 12, 20, 21]. Among the five patients who underwent these procedures, diplopia and strabismus resolved postoperatively in the three patients [11, 20, 21]. However, end-to-end anastomosis is not always possible during surgery because of anatomical and technical challenges. For these reasons, anastomosis was not performed for any patient with CMs involving CN III and VI. Moreover, the exact reason for the improvement in patients’ symptoms after an anastomosis remains to be identified. Whether this improvement is due to Wallerian degeneration occurring in the thinnest CN IV or because of the patients’ adaptation based on specific characteristics of CN IV palsy is debated in the literature [11, 20, 21].
Surgical resection was the primary treatment modality in our study, whereas three patients were treated conservatively [10, 18, 28]. Itshayek et al. reported that no neurologic deficits occurred postoperatively for 18 months after a craniotomy and exploration of the interpeduncular cistern in their patient who did not have any CN deficit . A 3-month-old baby with non-progressive neurologic deficit was managed conservatively because of high surgical risk; nevertheless, the patient showed signs of recovery . Symptom progression due to CMs of the ocular motor CNs is also associated with repeated intralesional hemorrhage. Progressive worsening of CN deficits could be an indication for surgical treatment of CMs. Aggressive surgical intervention could cause new deficits due to the manipulation of ocular motor CNs in patients with stable symptoms. Thus, surgery must be carefully considered as a preventive therapy for patients with asymptomatic lesions.
An understanding of the natural history of the disease aids with the treatment strategy. For general CMs, the annual rate of hemorrhage is 0.6% in patients without prior hemorrhage and 4.5% in patients with prior hemorrhage . Other studies have reported that the hemorrhagic rates vary from 0.25–3.1% per patient-year , or that the annual bleeding rate of patients can be 0.25%-20% regardless of the lesion location in the brain . In our study, although the exact rate of hemorrhage could not be elucidated, no patient had reported re-bleeding after STR and conservative care. Advanced imaging techniques facilitate the radiological diagnosis of these lesions and could aid in a better understanding of the natural history of CMs of ocular motor CNs.
In our study, the most appropriate surgical treatment for functional preservation was nerve continuity preservation. CMs are not only adhesive but can also invade the neural tissue of the CNs [20, 21]. Irrespective of the severity of involvement, CMs are not fatal and are not associated with mortality, even when resected partially such as in STR. The CN deficits are mainly attributable to the mass effect of the CM and irritation from re-bleeding [2, 3]. Relieving the mass effect in itself can recover part or complete CN function. Therefore, the primary surgical principle should focus on preserving nerve continuity. Some authors have reported that STR has the risk of recurrent bleeds [1, 2, 16]; however, no patient examined experienced recurrent bleeding after STR in our study. Of course, GTR with nerve continuity preservation is the ideal standard of care, but it is not always possible. The CMs are contained within a pseudocapsule, and therefore, performing a minimal resection of hemosiderin-stained tissue and traction of CN with sharp dissection is important for preserving nerve continuity and function of the ocular motor CNs during surgical treatment of CMs [1, 12, 14, 17].
Our study had some limitations, which hindered the better characterization of the treatment methods for CMs of the ocular motor CNs. First, it was difficult to investigate the role of extent of resection on the functional outcome and re-bleeding after treatment because the existing literature is limited to small numbers and isolated case reports. Therefore, we focused on the role of nerve continuity preservation during surgery rather than the extent of resection. Second, the appropriate follow-up period after treatment could not be identified in our study because most reports did not present the follow-up period. However, CMs are not malignant; therefore, further study should assess the natural course of the disease, including cases of re-bleeding.