Schwannomas originate from the myelin sheath of peripheral nerves and are mostly benign, accounting for approximately 8% of central nervous system (CNS) tumors. Vestibular schwannoma is the most common, but schwannomas occurring in the brain ventricle or parenchyma are extremely uncommon (1, 2). Ectopic schwannomas (ES) refer to schwannomas occurring in the brain parenchyma or ventricles and are rare in the lateral ventricle (3). The first case of lateral ventricular ES(LVES)was reported by David in 1965 (4), and thus far, only 23 cases have been reported in the English literature. Of these, only one case of malignant biological behavior was reported (5).

Herein, we report a case of right LVES, which was misdiagnosed as a meningioma before surgery. To obtain a better understanding of LVES, this study reviewed the relevant literature on LVES to summarize and analyze the clinical manifestations, pathologies, imaging features and progress.

Schwannomas are benign tumors that arise from nerve sheath cells and are commonly found in the head, neck, and limbs. Intracranial schwannomas account for approximately 8% of CNS tumors. Schwannomas occurring in the brain ventricle or parenchyma are extremely rare (1, 2). LVES is extremely rare, with only 23 cases reported thus far (6).

Although the origin of ES remains unknown, four theories have been proposed: (1) tumor transformation of the autonomic nerve tissue in the perivascular choroid plexus; (2) the transformation of multipotent mesenchymal cells into Schwann cells after tissue injury; (3) the transformation of ectopic fragments of neural crest cells into tumors in the ventricular system during abnormal embryonic development; and (4) the possibility of transformation of mesoderm-derived mesenchymal leptomeningeal cells in the brain into Schwann cells (7–10). In our case, ES was at the posterior horn of the right lateral ventricle, which was closely associated with the choroid plexus during the operation. The tumor transformation of autonomic nerve tissue originating from the perivascular choroid plexus is a reasonable explanation of our case.

Of the 23 cases ( Table 1 ) (4–8, 11–27), LVES was more common in men (74%, 17/23) than in women and was mostly located on the right side (78%, 18/23). The average age at clinical presentation is 28 years, with an age range between 8 and 68 years ( Figure 4 ). Moreover, most cases are histologically benign, except in one case of malignancy, in which the patient developed recurrence and metastasis of the tumor (5). The main clinical symptoms of the patient who had malignancy were headache and vomiting, which are similar to the symptoms of most of the reported benign intraventricular schwannomas. Meanwhile, the patient was 40 years old, while we found that 16 of the 22 benign patients were younger than 40 years old. Therefore, malignancy should be suspected in older patients with intraventricular tumors. In addition, the patient was rehospitalized seven months after the first surgery and presented with severe headache and vertigo. Brain MRI revealed tumor recurrence and metastasis. The rapid clinical course was different from the reported cases of benign tumors.

Surgical resection is considered to be curative. Most patients have good results after surgical removal of the tumor ( Table 1 ). Of the 21 benign cases reported in previous studies, there was no recurrence of LVES during long-term follow-up after surgery. In our case, the patient, with a completely excised tumor, also had a good outcome after 1 year of follow-up. However, if schwannomas can be accurately identified preoperatively, can gamma knife therapy be considered for small tumors such as small acoustic neuromas?

These tumors cause symptoms that depend on where they are located. The most common symptoms are headache and epilepsy. Of the 23 previously reported cases, except for 4 cases where the symptoms were not recorded, 12 of the patients presented primarily with symptoms such as headache, which may be caused by the mass effect of the tumor (7). In our patient, daily dizziness of gradually increasing intensity, associated with fatigue, nausea and vomiting, was the main clinical manifestation. However, we do not think the patient’s symptoms had much to do with the tumor, or even that the patient’s tumor was an accidental discovery. Unfortunately, the patient was not given more in-depth investigation to support our hypothesis. A review of the clinical features of LVES is shown in Table 1 .

Immunohistochemical staining is indispensable for the diagnosis of ES. Sometimes it is difficult to distinguish it from meningioma visually and microscopically. S-100 and vimentin are typically positively expressed, while GFAP and EMA are often negatively expressed (7, 25). Through a literature review, we found that some cases appeared as misdiagnoses based on the preoperative and intraoperative frozen section, and the misdiagnoses included ependymoma, cystic astrocytoma, cystic meningioma, hemangioblastoma, fibroblastic meningioma, papilloma and choroid plexus carcinoma (8, 14, 16, 18, 21, 27). In addition, the majority of the 23 cases were diagnosed as LVES based on the pathological findings. Microscopically, the tumor cells can be divided into two types. Antoni A region: cells are often arranged in fusiform; and Antoni B region: cells are often arranged as palisade patterns.

In terms of imaging features, LVES has specific characteristics. MRI is the best diagnostic tool for these tumors because it can be used to determine the location of the ventricles and the relationship between the tumor and choroid plexus.Combined with this case and related literature, these characteristics are summarized as follows. Cystic changes: cystic and solid changes are characteristic of this disease. The cystic part is mostly manifested as low signal intensity on T1WI and high signal intensity on T2WI, while the solid part is often characterized by slightly low signal intensity on T1WI and high signal intensity on T2WI.Moreover, contrast-enhanced MRI showed significant enhancement in the solid but not cystic areas. Edema: peritumoral edema is considered characteristic of benign schwannomas. ES is characterized by peritumoral edema of different degrees (23). Calcification: A previous study reported that part of LVES may exhibit calcification (28), which is helpful for the diagnosis of these tumors to some extent. Among the MRI findings of these 23 LVES cases, cystic changes and edema were more common. Cystic changes were found in 12 patients, and edema was found in 11 patients. Calcification was observed in only 4 patients. In our case, the patient presented with cystic and solid changes and mild edema around the lateral ventricle, and these findings are consistent with previous literature. In addition, whether tumors showing lobulated changes are more likely to be schwannomas is worth considering in future cases.

The origin of LVES could be the tumor transformation of autonomic nerve tissue in the perivascular choroid plexus. Lateral ventricle tumors are rare benign lesions with good prognosis after surgical resection, and LVES should be considered in the differential diagnosis. Moreover, whether ES could be considered for gamma knife treatment, such as a small acoustic neuroma, requires further investigation.

All authors contributed to the diagnosis and treatment of the patient. YuL and YX drafted the work and wrote the manuscript. HZ and JZ edited the manuscript, substantively revised it, and approved the re-submitted version. HL and XH provide substantial help to the writing of the article. XH and YuL made substantial contributions to the treatment and diagnosis of the patient. All authors contributed to the article and approved the submitted version.