Background

Schwannoma is a benign, encapsulated nerve sheath tumour composed of primarily Schwann cells in a poorly collagenised stroma. Plexiform schwannoma (PS) is an extremely rare and unique variant of Schwann cell tumours characterized grossly and histologically by multinodular architecture and the individual thin capsule (Ijichi et al., 2017). It comprises up to 5% of all schwannomas (Kudose et al., 2016). Most cases of PS occur in the skin and subcutaneous soft tissue, and approximately 20% of PSs are located in the head and neck region (Berg et al., 2008; Kohyama et al., 2011). In this report, the rare case of PS occurred in the CPA region. This is thought to be the first case report of PS growing from this region and the facial nerve. We hereby report this case, illustrating that PS has very few differential features, as well as presenting the characteristics of clinical and imaging diagnosis.

1 Case Presentation

The patient was a 32-year-old woman in good health. She had a one-month history of worsening verbal vagueness associated with unstable gait. Following diagnosis, patient was referred to our hospital. Physical examination revealed positive Romberg’s sign.

Magnetic resonance imaging (MRI) of brain, with and without gadolinium, revealed a mass in the cerebellopontine angle space (Figure 1(a-f)). It was hypointense on T1-weighted imaging and hyperintense on T2-weighted imaging with heterogeneous enhancement. Based on imaging characteristics, primary considerations included schwannoma, or ependymoma. She did not have other problems in his medical or family history. The tumor was excised completely. During the operation, the mass was visible at subdural and ventral brain stem. It was an encapsulated tumor mass with a fairly firm and smooth surface. The lesion contains multiple cystic changed and was pushing the brain stem and cerebellum laterally to the right. It was also revealed that posterior cranial nerve (facial nerve) went through the mass. The intraoperative pathological diagnosis was plexiform schwannoma involving the foramina jugulare.

Cyst compartments presented with slight hyperintense signal compared with cerebral spinal fluid (CSF) on T2-weighted images; and solid compartments showed slight hyper signal intensity on T2-weighted and FLAIR images compared with parenchyma. Contrast-enhanced T1-weighted images showed heterogeneous enhancement. The individual nodules of the tumor were surrounded by a thin low-intensity capsule or septa on T2 weighted images. No perilesional edema was noted. The fourth ventricle was compressed and shifted to the right upper side.

2 Disscussion

Plexiform schwannomas have been reported to represent 4.3 % of all schwannomas (Nagata et al., 2015). Studies have reported approximately 23% of all PSs arise in the head and neck region (Ijichi et al., 2017). While PS located in the head and neck have been reported in literature, none of the reported tumors were presented in the CPA space.

Clinically, schwannoma is seen commonly in adults of the age group ranging from 10 to 40 years with female predilection of 2:11 (Lambade et al., 2013). Our case showed the same features to the literatures. The symptoms of our case were related to the site of the tumor showing nonspecific features.

The most unusual feature in our case was the site, i.e. involvement of the CPA which has not been documented as a location up to now. Consider the site of our case, an assumption that the association with posterior fossa nerve can be made, although the nerve was not identified at the time of MRI scan. A solid-cystic mass, with intense enhancement of the solid compartment, was detected around the fourth ventricle area pre-operatively. The lesion was seen extending into the left CPA region. Since the tumor in our patient appeared to be originating from the fourth ventricle, its diagnosis including ependymomas, followed by choroid plexus papillomas and medulloblastomas were considered. In general, the latter two tumors contain more solid compartment. The multi-cystic pattern and its location, therefore, provide very valuable imaging indicators of ependymomas. Retrospectively, we repeated analysis of the pre-operative MRI images of the tumor. Virtually, the tumor was growing around the fourth ventricle, rather than from the ventricle. By looking it over, the fourth ventricle was demonstrated situated at the right side of the tumor, and was compressed by the mass and shifted off the midline. Furthermore, the trianglular solid compartment was pointing into the CPA, with strong association with the left acoustic nerve root. Despite these evidences may be not enough to suggest the tumor arising from the nerve, they indicated the origination from the CPA region.

Apart from the site, some radiological characteristics are worth to note, i.e., the correlation between the MRI intense signals and the tumor characteristics. Reviewing of the literature revealed some distinctive features of PS including the multinodular architecture and the individual thin capsule, but rarely any case of its radiological and pathological relation was detected. MRI images showed the tumor was solid-cystic due to the heterogeneous intense signals presented. Moreover, these cystic compartments presented with slight hyperintense signal compared with cerebral spinal fluid (CSF) on T2-weighted images; and solid compartments showed slight hyper signal intensity on T2-weighted and FLAIR images compared with parenchyma. Taking the radiological findings for this tumor into consideration, the diagnosis of schwannoma was made. As schwannoma is a benign, encapsulated nerve sheath tumour composed of primarily Schwann cells in a poorly collagenised stroma, we can postulate the hypothesis that MRI images might indicate the essential pathological features of conventional as well as plexiform schwannoma including compact and/or loose texture (Antoni A and/ or B tissues) (Berg et al., 2008).

3 Conclusion

In summary, we describe the first case of a facial nerve originated and CPA PS. MRI images might indicate the essential pathological features of conventional as well as plexiform schwannoma.

Authors’ contributions

Liang Zong-hui conceived and designed the work that led to the submission. Dou Ya-fang and Liang Zong-hui evaluated images and analyzed data. Dou Ya-fang completed the writing of the article. Liang Zong-hui revised the paper. All authors participated in paper writing and approved the final manuscript.

Acknowledgments

This work was supported by the Shanghai Jing’an District Health System talent training Plan discipline leader, project number JWRC2014D04.

Reference

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