Literature Review and Case series
Among our patients, one of them was considered to be a craniopharyngioma involving the suprasellar region, according to MRI. One case consisted of a rather small, instead of a giant, aneurysm but still caused hydrocephalus. One patient with aneurysm rupture had central neurogenic shock and massive cerebral infarction. All masses block or oppress the third ventricle and cause hydrocephalus, which can also be found in most of previous cases. Our cases showed features of this disease in one hospital to minimize between-group differences at baseline. In addition, our cases are unique in that the giant aneurysms were detected by CTA instead of DSA for the first time, which is considered the gold standard for aneurysm diagnosis. CTA is a standard preoperative examination in our intracranial tumor surgical procedure for detecting aneurysms before craniotomy. Several studies have determined that CTA can replace DSA for aneurysm diagnosis,28–30 especially for giant aneurysms.31, 32 We used CTA to diagnose giant aneurysms mimicking intraventricular tumors and used it as the main index of follow-up after aneurysm coil occlusion procedures, and the results of CTA are precise and stable. Aneurysms presenting as third ventricular masses have been studied in several limited cases between 1979 and 2020 because of the infrequency of this disease. This study aimed to systematically review previous studies and our new series of five cases to determine the outline of aneurysms presenting as third ventricular masses on neuroimaging, treatment, and follow-up outcomes and to add more necessity to preoperative CTA before craniotomy.
We reviewed the literature from PubMed and Embase databases and identified 27 cases of aneurysms (including the cases above) presenting as third ventricular masses.8–26 The average age of the patients was 62 years (range, 14–82 years). In previse cases, all patients were middle-aged and elderly, with one of our cases (case 1) being the first adolescent reported. Case 1 suggests that giant intracranial aneurysms can cause hydrocephalus in adolescents and children, so aneurysms should be included in the differential diagnosis of hydrocephalus and intracranial hypertension in adolescents. The female-to-male ratio of the patients was 14:13. All aneurysms were angiographically positive except for one case from Liu et al., which is a case of a completely thrombosed aneurysm for which angiographic studies were negative.16 Case 3 in our series was also a thrombosed aneurysm that required more than angiographic studies, and other examinations such as MRI and blood coagulation function should be included before treatment. In case 3, CTA reconstruction imaging showed greater precision than DSA. Our case is unique in that it used CTA to diagnose and depict the aneurysm when all other cases from the literature review did not apply this modality to diagnose the existence of the aneurysm. It is also the first case to use CTA in follow-up. The basilar artery is the most common artery with giant aneurysms presenting as third ventricular masses (21 of 27 cases), while others develop in the anterior communicating artery, posterior communicating artery, anterior cerebral artery, and middle cerebral artery. The symptoms of these cases are similar, with nearly all cases presenting symptoms and signs of hydrocephalus or intracranial hypertension, except for one case from the literature review that presented as intramural hemorrhage and then disastrous hemorrhage.13 Other symptoms are diverse, including seizure,9 ataxia, dementia, and hemianopia. In previous cases, intracranial hemorrhage13, 22, 23, 26 and aneurysm rupture11, 13, 26 occurred in some cases, and all aneurysm ruptures resulted in the death of the patients; other causes of death included thrombogenesis,25 cerebral infarction, intraoperative hemorrhage,10 and intraoperative cardiac arrest.8 Cerebral infarction (cases 2, 3, and 5) and intracranial hemorrhage (cases 3 and 5) both occurred in our series. In previous cases from literature review, all patients received CSF diversion, and nine patients only had CSF diversion without treatment of the aneurysm. In our five cases, all patients received treatment of the aneurysm, while treatment exclusively for CSF diversion, such as ventriculoperitoneal (VP) shunt, was not applied to cases 2 and 4. The most commonly used procedure to treat aneurysms was aneurysm coil occlusion (nine of 23 cases), and this treatment has been most commonly applied in the last ten years.
Preoperative Neuroimaging Examination
It is very important in clinical practice to select simple and effective examination methods among various neuroimaging techniques to improve the diagnostic accuracy of brain space-occupying lesions. In cases we gathered, all patients were hospitalized with clinical presentation and received a CT scan or MR scan as the preferred inspection. All the third ventricular masses were found in the first neuroimaging examination, and characteristics such as the size of the lesion and hydrocephalus were identified. Although MRI provides precise location of the mass and the relationship of the lesion to surrounding structures, and CT scan can detect mural calcification, it is difficult to differentiate giant intracranial aneurysms from intraventricular tumors. In addition, this type of patient is usually received by the neuro-oncology department instead of the cerebrovascular surgery department, which has less experience of aneurysms, meaning that craniotomy could take place for the resection of the “tumor,” which is very hazardous for the patient. Intraoperative hemorrhage has been reported in previous literature.10 Furthermore, in one case, the aneurysm, determined under neuroendoscopy, was mistakenly taken as a hematoma.23 To avoid such adverse events, angiography is required to determine the substance of the lesions. DSA remains the gold standard for evaluating intracranial aneurysms with excellent spatial and temporal resolution. In previous cases, DSA was used as the gold standard for diagnosis. Magnetic resonance angiography (MRA) was used in some cases alongside DSA with no reports of misdiagnosis in cases we collected, and one case reported a positive result on MRA and negative result on DSA.24 The DSA for case 3 in our series also did not obtain patent results because of thrombosis and calcification, the diagnosis was made comprehensively according to VW-MRI, CT, and DSA, suggesting that DSA is not the only choice for the diagnosis of giant aneurysms. DSA evaluates the circulation of aneurysms, which is not enough for complex cases such as aneurysms presenting as a third ventricular mass. Luminal size/patency evaluation, the relationship between aneurysms and surrounding structures, and the calcification of the aneurysmal sac, which are significant for evaluating aneurysmal rupture risk, choosing treatment methods, and making prognosis, cannot be obtained through DSA.33, 34 In cases of giant aneurysms and aneurysms with mass effect, angiographies like CTA and MRA present a more comprehensive evaluation than DSA.
Use of CT angiography
CT angiography is increasingly becoming a diagnostic tool for vessel pathology.31 Aneurysms larger than 3 or 4 mm can be recognized with CTA. Teksam et al. reported that CTA missed only seven out of 106 cases, and of these, only two were larger than 4 mm.30 In cases with aneurysm rupture and cerebral hemorrhage, which may require emergency surgical evacuation, CTA is a quick and obviously better vascular evaluation tool than DSA. Because calcification often appears in vessel pathology and non-cooperative patients make MR or MRA impossible, CTA also has advantages over MRA in certain aspects. According to a recent study on imaging morphology,32 because of the multipass or recirculation phenomenon of the contrast medium within the aneurysm, CTA is superior to 3D Time-of-Flight MRA, contrast-enhanced MRA, and even to DSA in the visualization of the patent aneurysmal lumen.35 All these characteristics of CTA made it suitable for the evaluation of giant intracranial aneurysms, but it was not applied in all cases reported in the literature of giant aneurysms adjoining the third ventricle. Our study’s reporting of CTA as a diagnostic and follow-up examination and the resultant precise evaluations filled the void of neuroimaging examination of this rare and complex disease. All five patients underwent CTA, which revealed aneurysms before surgery and at postoperative follow-up. CTA reconstruction imaging of the intracranial arterial system is reliable and economical for revealing intracranial aneurysms. CTA has become an imperative preoperative neuroimaging examination for patients with skull base tumors in our ward. With preoperative CTA, misdiagnosis of a third ventricular aneurysm and other vascular malformations can be discovered at an acceptable cost. However, CTA has limitations, such as beam-hardening artifacts related to coil embolization in postoperative patients, which can be found in all of our follow-up CT/CTA examinations. However, due to its viability, fast imaging, and high spatial resolution, it remains the first choice to follow-up postoperative patients with aneurysms.
Vessel wall magnetic resonance imaging
Another neuroimaging examination we applied was VW-MRI, a neuroimaging technology for indicating inflammatory processes in vessel walls. Enhancement of the aneurysm wall on VW-MRI is assumed to be an imaging marker of aneurysm instability and a higher risk of rupture.36, 37 Case 3 in our series underwent VW-MRI before surgery to evaluate the risk of aneurysm rupture because of discontinuous calcification surrounding the rim of the aneurysm found on CTA. The patient’s diabetes may contribute to the risk of aneurysm rupture and hemorrhage. Patients with diabetes had a significantly higher prevalence of calcification and high-risk plaques on vessel walls, which are risk factors for aneurysm rupture and hemorrhage.38 Interestingly, some recent research suggests that diabetes could be a protective factor against the rupture of intracranial aneurysms.39, 40 Enhancement of the aneurysm wall and anterior cerebral artery was significant in our case according to VW-MRI. The aneurysm appeared clear with a thrombus on MRI imaging. Considering the thrombus inside the aneurysm alongside the mass effect it caused, aneurysm clipping and aneurysmectomy were applied as a confined operation. Aneurysm wrapping was performed to prevent hemorrhage. However, hemorrhage still occurred after two weeks. The results demonstrate the value of VW-MRI in evaluating the risk of aneurysm rupture in a certain way.
In conclusion, intracranial aneurysms at critical positions, such as the third ventricle, or aneurysms causing clinical syndromes require multiple neuroimaging examinations for differential diagnosis and treatment planning.
Cerebrospinal fluid diversions due to obstruction of the third ventricle caused by giant aneurysms
All patients reported had different degrees of hydrocephalus or intracranial hypertension. Certainly, there is no optimal management option for this delicate and complex situation. CSF diversions had been performed in most patients as a symptomatic treatment to relieve the brain from CSF pressure. Multiple methods are available, including VP shunting, ventriculoatrial (VA) shunting, eternal ventricular drainage (EVD), ventriculostomy with craniotomy, and endoscopic third ventriculostomy (ETV). VP shunting was the most commonly used procedure in the past, with 12 of the 27 patients undergoing this procedure, though all 12 cases were from 10 years ago. Six of the 27 patients received ETV. Four of the 27 patients received EVD, including one case from our series who received EVD for postoperative intracranial hemorrhage. Three of the 27 patients underwent ventriculostomy with craniotomy, including two cases in our series. Two of the 27 patients underwent VA shunting. A previous study showed that VP shunting41 is the most common type of shunting procedure because it is convenient and effective, and studies have shown no significant differences in terms of the outcome between the different kinds of shunting methods (VP, VA, and lumboperitoneal shunting). ETV is becoming widely used because of the improvements in neuroimaging, operation instruments, and stereotaxic neuronavigation systems in recent years. A meta-analysis based on randomized controlled trials revealed that in obstructive hydrocephalus, ETV had significantly lower blockage rates and could reduce the risk of postoperative hematoma compared with VP shunting.42 But in our study, the death rate was much higher in the ETV group (three of 6) than in the VP shunting group (three of 12). These deaths were caused by aneurysm rupture and hemorrhage. According to a literature report, reduction of intracranial pressure after CSF diversions can increase the aneurysmal transmural pressure, shift the formed clot inside the aneurysms, and cause a higher risk of rupture.43–45 Therefore, according to the theory, ETV should be performed with other treatments to stabilize or remove aneurysms. The case results fit this theory: only one out of three deaths among patients who received ETV was caused by aneurysm rupture (the other two were caused by thrombosis), and that case is the only one without treatment for aneurysms. Ventriculostomy with craniotomy has the same mechanism as ETVbut with a different approach, which means it can cause a higher risk of rupture. The appropriate operation combination should be aneurysm clipping and ventriculostomy under one craniotomy, which is safe and less damaging to patients. All three cases attended to receive this combination of treatments, and case 1 finally underwent aneurysm coil occlusion because the aneurysmal neck was not clear. Two cases (cases 2 and 4) did not receive any CSF diversion because the hydrocephalus was mild, and symptoms of cranial hypertension were not typical. Which procedure is the optimal choice for hydrocephalus caused by a giant intracranial aneurysm mimicking an intraventricular tumor? Should aneurysms be treated before CSF diversions in certain cases, according to the theory? Further investigation and clinical evidence are required to answer these questions.
Treatments for Aneurysms
General treatment of aneurysms includes surgical clipping and endovascular management (mainly aneurysmal coiling).46 Generally speaking, outcomes in patients treated with coiling are better than surgical clipping in terms of long-term dependency and mortality rate.47 With various methods to treat hydrocephalus, the options for aneurysms are limited, and the aneurysm neck is usually not clear (e.g., Case 1) or too broad to clip. In our literature review, only two patients received aneurysm clipping, and eight patients received aneurysm coil occlusion. Interestingly, two patients who underwent aneurysm clipping had an excellent prognosis when the results of aneurysm coil occlusion were not satisfactory. After these patients underwent aneurysm coil occlusion, one died from cerebral infarction; one died from thrombogenesis of the basilar artery;25 one had hydrocephalus21 and received a second operation; one’s aneurysm developed and progressively compressed the right thalamus and midbrain, and received a second operation;20 and one died from aneurysm rupture.11 Only two patients (including the present case) received satisfactory results,19 and one patient’s prognosis was not reported.23 In our cases, the results were more favorable: two patients (case 1 and case 4) who received aneurysm coil occlusion achieved good prognosis, particularly case 1, who underwent follow-up after aneurysm coil occlusion for two years and obtained favorable prognosis; and two of the three patients (case 2 and case 3) who underwent aneurysm clipping had unfavorable prognosis due to post-operation hemorrhage. A previous study of middle aneurysms showed that cerebral infarction was the main cause of death after two kinds of treatment,48 and clipping had a lower death rate (0.3–1.1%), which may be indicative of our cases. Nevertheless, aneurysms presenting as third ventricular mass are mostly giant aneurysms with hydrocephalus; the prognosis of this disease is much worse, the operation is much harder than for general middle aneurysms. Developing a standardized treatment protocol with limited case reports and huge heterogeneity between cases is difficult. Based on the evidence above, we believe that aneurysm coil occlusion with CSF diversion, if necessary, is a favorable option for treating giant aneurysms presenting as third ventricular masses with hydrocephalus.
Based on the results presented above, the treatment for giant intracranial aneurysms mimicking an intraventricular tumor is still non-ideal. It remains a complex and dangerous clinical challenge for both diagnosis and treatment. Neuro-oncology and cerebrovascular surgery departments should enhance communication and act with caution when encountering patients with unidentified third ventricular masses. Further investigations and case reports should be conducted in the future, especially preoperative examinations, to evaluate the rupture risks of giant intracranial aneurysms.