1. Introduction

Cystic cerebellar lesions present a diagnostic challenge due to the overlap between diverse etiologies. Even though the differential diagnosis list may include intracerebellar schwannoma, it remains a very rare entity with only 21 reported cases of cerebellar schwannomas documented to date in the English literature [1]. While cystic changes are a common feature of classical schwannomas, the presence of a cystic cerebellar lesion typically prompts consideration of a broader differential diagnosis, including more common entities such as hemangioblastomas or metastatic lesions [1]. The rarity of intracerebellar schwannomas, coupled with their nonspecific radiological appearance, can lead to diagnostic uncertainty and potential misdiagnosis. Furthermore, the absence of a family history of neurofibromatosis in this patient further underscores the uniqueness of this case and the potential for sporadic occurrence of these rare tumors [1]. In this case study, we report a case of a cystic intracerebellar schwannoma in a patient without any family history of neurofibromatosis.

2. Case Presentation

A 68-year-old male with a known history of prostatic hyperplasia presented with chronic headaches, dizziness, gait imbalance, and incoordination since October 2022. Three years ago, a brain MRI had revealed a cystic lesion in the right cerebellum, but due to the COVID pandemic and stable neurological condition, no further follow-up was conducted. However, a recent head CT followed by brain MRI demonstrated an increase in the size of the lesion, prompting referral to our institution (Figure 1).

Upon neurological examination, positive Romberg sign, abnormal coordination, dysmetria, and sensory deficits were observed. The patient exhibited left V1 V2 hypoesthesia, mild pronator drift on the right side, and left dysmetria. The gait examination revealed abnormal tandem walk.

MRI findings revealed a lesion in the right posterior fossa with a solid and cystic component, making it challenging to determine its exact nature. The differential diagnosis included ependymoma, hemangioblastoma, and other lesions with CSF trapping. Surgical intervention was deemed necessary to establish a definitive diagnosis and provide therapeutic management.

During the suboccipital craniotomy, intraoperative inspection revealed moderate swelling of the tumor surface. The drainage of the cystic component resulted in drainage of brownish fluid, indicating a history of intracystic bleeding.

Postoperative follow-up demonstrated an improvement in the patient’s symptoms, including headache relief and enhanced gait stability. The patient made a remarkable recovery with no evidence of neurological deficits following the surgical resection of the intracerebellar schwannoma. Postoperative brain MRI with gadolinium contrast enhancement performed 6 months after the surgery showed stable postoperative changes and no evidence of tumor recurrence. Figure 2 summarizes the timeline of this case.

The specimen showed a spindle cell neoplasm with typical features of a schwannoma (Figure 3). Elongate spindled tumor cells with ill-defined borders, fascicular architecture, and some nuclear alignment. The tumor was predominantly Antoni type A tissue. There was a well-demarcated border with adjacent cerebellar tissue. There was focal “ancient” type nuclear degenerative change, but no atypia or mitotic activity. Proliferation assessed by Ki 67 IHC was low averaging less than 2%. The full IHC and special stain profile was typical for schwannomas with strong S100 and SOX 10 positivity (SOX 10 nuclear) patchy CD34 positive with extensive pericellular reticulin deposition. The tumor was immunonegative for EMA, GFAP, IDH 1, inhibin, neurofilament, AE1/AE3, and melanoma cocktail.

3. Discussion

Intraparenchymal schwannomas are rare tumors that have been predominantly reported in the spinal cord rather than within the brain [2]. The first intracranial parenchymal schwannoma was described in 1965 [3]. This discussion aims to expand on intraparenchymal schwannomas and its pathogenesis, with a focus on cerebellar schwannomas. Literature review reveals that brain parenchymal schwannomas are primarily located in the upper tentorium, with only 21 cases of cerebellar schwannoma reported to date in the English literature [2]. Table 1 illustrates an updated summary of all reported cases of intracerebellar schwannomas. The histogenesis of intracerebral schwannomas remains controversial, and multiple theories have been proposed to explain their occurrence. One theory suggests that schwannomas arise from the proliferation of Schwann cells within perivascular nerve plexi ([20, 21]. These minute nerves may be present in the tela choroidea, the embryological precursor of the choroid plexus, which could explain the proximity of many tumors to the ventricular system. Furthermore, Schwann cells have been identified in subarachnoid space, and the peripheral areas of old cerebral infarcts and multiple sclerosis plaques. The occurrence of Schwann cells in these conditions may be attributed to proliferating multipotent mesenchymal cells, rather than mature Schwann cells accompanying perivascular plexi [22]. Another hypothesis suggests that intracerebral schwannomas may arise from neural crest elements displaced during embryogenesis [23]. The distribution and dynamics of stem cells in the central nervous system have not been fully elucidated, which further complicates the understanding of intracerebellar schwannoma pathogenesis. To gain a comprehensive understanding, detailed morphological analysis of intact tumors and surrounding tissues is crucial.

Cystic tumors can develop as a result of different factors including microhemorrhage, necrosis, or degeneration. These factors can result in the formation of a small cavity, followed by the formation of a continuous capsule [8, 23]. Most of these tumors are benign, and their clinical symptoms are typically associated with the specific location within the body. However, it is important to note that the clinical symptoms and imaging characteristics of these tumors are not distinctive, necessitating the use of both histological examination and immunohistochemical studies to confirm a diagnosis of brain parenchymal schwannoma.

Immunohistochemistry can reveal specific markers for this type of tumor, such as S100 protein (+), vimentin (+), and glial fibrillary acidic protein (GFAP) (−), among others [16, 24]. It is worth mentioning that brain parenchymal schwannomas are located within the brain tissue itself and do not exhibit any apparent association with the surrounding dura or cranial nerves.

This case report provides an opportunity to compare and contrast with previously documented cases, shedding light on the variability in clinical presentations, radiological features, and treatment outcomes associated with these uncommon tumors [1]. Unlike many previously reported cases that presented with symptoms of increased intracranial pressure or focal neurological deficits, this patient’s initial presentation with dizziness and nausea was relatively nonspecific [1, 15, 17–19]. This highlights the diagnostic challenge posed by intracerebellar schwannomas, as their symptoms can mimic more common pathologies, such as vestibular disorders or cerebellar infarcts [1, 15, 17–19].

Interestingly, the absence of a family history of neurofibromatosis type 2 (NF2) in this case contrasts with several previously reported cases, where intracerebellar schwannomas were associated with this genetic condition [1, 24, 25]. This underscores the potential for sporadic occurrence of these tumors, further complicating the diagnostic process [25].

The radiological appearance of the cystic cerebellar lesion in this case was initially suggestive of a broader differential diagnosis, including hemangioblastoma or metastasis. This overlap in imaging features with more common pathologies is consistent with the experience reported in previous cases, highlighting the limitations of relying solely on radiological findings for a definitive diagnosis [19, 25]. Consistent with the standard management approach for intracerebellar schwannomas, the authors pursued complete surgical resection, which is generally associated with favorable outcomes [18, 19]. The patient’s uneventful postoperative recovery and the absence of tumor recurrence on follow-up imaging align with the positive outcomes reported in several previous cases where complete resection was achieved [1, 18, 19]. However, it is important to note that some reported cases have experienced postoperative recurrence or residual tumor growth, necessitating additional interventions or close follow-up ([1, 24, 25] [10]; [9]). This variability in outcomes underscores the need for long-term surveillance and the potential role of adjuvant therapies, such as radiation therapy, in select cases [24].

In summary, this case report contributes to the growing body of literature on intracerebellar schwannomas by highlighting the diagnostic challenges, variable clinical presentations, and the importance of complete surgical resection for optimal outcomes. By comparing and contrasting with previously reported cases, the authors provide valuable insights into the management of these rare tumors and emphasize the need for continued research to improve diagnostic accuracy and treatment strategies.

4. Conclusion

Intraparenchymal schwannomas are rare tumors that are more commonly found in the spinal cord than in the brain. The pathogenesis of these tumors remains controversial, with theories involving Schwann cell proliferation, neural crest displacement, and metaplastic changes in soft membrane cells [1, 2, 22]. Further research and detailed morphological analysis are necessary to fully understand the pathogenesis of intracerebellar schwannomas [1, 16]. Nonetheless, most cases can be successfully treated with complete surgical removal, and the prognosis is generally favorable, without the need for additional radiotherapy or chemotherapy [1].

Ethics Statement

The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). Informed consent was obtained. Consent to publish was obtained.

Conflicts of Interest

The authors declare no conflicts of interest.

Author Contributions

Mohamed Alhantoobi: contributed to the conceptualization, methodology, data collection, and writing & editing. Nadeen Alkhoori: contributed to the conceptualization and methodology and writing—review & editing. Hassan Khayat: contributed to data collection and writing—review & editing. Euan Zhang: contributed to data collection and writing—review & editing. Almunder Algird: contributed to methodology, supervision, data collection, and writing—review & editing. John Provias: contributed to the project creation, supervision, conceptualization, methodology, guidance, and writing—review & editing.

Funding

The authors received no specific funding for this work.