Isolated cerebellopontine angle neurosarcoidosis mimicking meningioma: a diagnostic pitfall. Illustrative case

Abstract

BACKGROUND

Neurosarcoidosis (NS) is a rare inflammatory disease that can mimic intracranial neoplasms. Its presentation as an isolated cerebellopontine angle (CPA) mass is exceedingly uncommon and typically resembles vestibular schwannomas or meningiomas, complicating the diagnostic process.

OBSERVATIONS

A 25-year-old man presented with progressive diplopia and hearing loss. MRI revealed a diffusely enhancing lesion in the left CPA. Because the initial workup was inconclusive and intraoperative pathology heavily favored a nonneoplastic inflammatory process, subtotal resection was performed. Histopathological examination revealed a histiocyte-rich inflammatory infiltration with occasional multinucleated giant cells. The patient was treated with high-dose corticosteroids and experienced a good recovery.

LESSONS

This case underscores the importance of including NS in the differential diagnosis of CPA tumors, particularly in young patients with atypical features. Early consideration and histopathological confirmation are crucial to avoid unnecessary extensive resection and to enable timely initiation of appropriate medical therapy.

https://thejns.org/doi/10.3171/CASE2668

Sarcoidosis is a systemic granulomatous disease of unknown etiology, characterized by the formation of noncaseating granulomas in affected organs.¹ Neurological involvement, termed neurosarcoidosis (NS), occurs in approximately 5%–15% of patients with sarcoidosis and is known for its highly variable manifestations.² NS can affect virtually any part of the CNS and often mimics primary or secondary intracranial tumors.³

When NS presents as a solitary lesion in the cerebellopontine angle (CPA), it poses a significant diagnostic challenge. The CPA most commonly harbors vestibular schwannomas and meningiomas, which together account for the majority of tumors in this region.⁴ NS in this location is exceedingly rare and can radiographically mimic these more common entities on MRI.^5,6 Misdiagnosis may therefore lead to unwarranted surgical intervention for a condition that is often amenable to medical therapy.^1,7

We report the case of a young adult man with an isolated CPA mass that was ultimately diagnosed as NS on biopsy.

Illustrative Case

A 25-year-old man with no significant past medical history presented with a 6-month history of progressively worsening diplopia and left-sided hearing loss. Given the atypical clinical presentation and to rule out infectious, inflammatory, or malignant etiologies such as CNS lymphoma or metastasis, a comprehensive systemic evaluation was conducted. Initial investigations included CSF analysis and excisional biopsy of a suspected cervical lymph node, both of which were nondiagnostic. The CSF demonstrated moderate lymphocytic pleocytosis but no malignant cells or infectious organisms, while the lymph node biopsy showed reactive changes without evidence of granulomas or malignancy. Furthermore, comprehensive body imaging, including CT of the chest, abdomen, and pelvis, revealed no hilar lymphadenopathy, pulmonary infiltrates, or other systemic lesions. This absence of systemic involvement confirmed that the patient’s condition was uniquely isolated to the CNS. Over the ensuing months, the patient’s symptoms continued to progress, and serial imaging demonstrated enlargement of the CPA lesion. He was therefore referred for neurosurgical evaluation.

MRI of the brain revealed a diffusely enhancing mass in the left CPA, without clear separation from the adjacent dura (Fig. 1). The radiological differential diagnosis included vestibular schwannoma, meningioma, and, less likely, an inflammatory or infectious process. Given the diagnostic uncertainty and interval lesion growth, an open biopsy was performed via a left retrosigmoid craniotomy.

FIG. 1.

Preoperative MR images of the left CPA lesion. A: Axial T1-weighted contrast-enhanced MR image demonstrating a diffusely enhancing mass compressing the brainstem. B: Axial T2-weighted MR image demonstrating the lesion’s relationship with the adjacent cisterns.

Intraoperatively, the mass consisted of infiltrative yellow-pink granulomatous tissue that was firmly adherent to the dura and adjacent critical neurovascular structures, an appearance atypical for common CPA tumors. Frozen-section analysis suggested a nonneoplastic histiocytic (inflammatory) lesion. Because the intraoperative pathology heavily favored a nonneoplastic inflammatory process, and the lesion was firmly adherent to the cranial nerves and brainstem, the surgical team elected to limit the intervention to a subtotal resection. A gross-total resection was deliberately avoided to prevent severe iatrogenic cranial nerve morbidity.

Definitive histopathological examination revealed a dense inflammatory infiltrate with plasma cells, lymphocytes, and various histiocytes. Various numbers of multinucleated giant cells were also easily identifiable (Fig. 2). Immunohistochemical staining was negative for Langerhans cell markers (CD1a and langerin), BRAF V600E, and lymphoid lineage markers, effectively excluding Langerhans cell histiocytosis, certain gliomas, and CNS lymphoma. In addition, special stains and cultures for infectious organisms, including acid-fast bacilli and fungi, were negative, arguing against infectious granulomatous etiologies. Collectively, these findings established the diagnosis of NS involving the CPA.

FIG. 2.

Histopathological examination. A: Low-magnification photomicrograph revealing diffuse inflammatory infiltrate. H&E stain, bar = 100 µm. B: High-magnification view showing a mixed inflammatory infiltrate with various histiocytes and multinucleated giant cells. H&E stain, bar = 50 µm.

Postoperatively, the patient recovered well, and high-dose corticosteroid (0.5 mg/kg/day prednisolone) therapy was initiated for NS. He was discharged on postoperative day 6 in stable condition without any new neurological deficits. Given the chronic and potentially relapsing clinical course of NS, long-term clinical and radiographic surveillance is essential. Our long-term follow-up plan includes regular outpatient neurological evaluations accompanied by contrast-enhanced MRI of the brain at 3- to 6-month intervals to closely monitor the lesion’s response to medical therapy. Routine transition to steroid-sparing immunosuppressive therapy will be strongly considered if there is evidence of radiographic progression, symptom recurrence, or if prolonged steroid therapy is poorly tolerated.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

Observations

Many CPA lesions are benign neoplasms, most commonly vestibular schwannomas or meningiomas.⁴ Consequently, in the absence of known systemic sarcoidosis, NS is typically not high on the differential diagnosis for a CPA mass.^2,5 However, NS can be the first and only manifestation of sarcoidosis in some patients. Indeed, up to 20% of NS cases occur in patients without any evidence of systemic disease.^8,9 The extreme rarity of isolated CPA involvement by sarcoidosis further contributes to the diagnostic challenge.

Only a limited number of NS cases involving the CPA have been reported. A 2019 review identified only 8 published cases of isolated CPA NS at that time.⁵ The reported cases in this review demonstrate that patients typically present with cranial neuropathies mimicking more common CPA neoplasms, most notably sensorineural hearing loss, tinnitus, dizziness, facial numbness, and diplopia. Given the lack of pathognomonic radiological features, the vast majority of these patients historically underwent resection under the presumptive preoperative diagnosis of a meningioma or schwannoma.^5,10–14

Regarding clinical outcomes, while aggressive upfront resection of CPA NS carries a substantial risk of cranial nerve morbidity (such as permanent hearing loss or facial nerve deficits),¹⁰ conservative surgical approaches (e.g., biopsy or subtotal decompression) combined with medical therapy often yield favorable results.¹³ Corticosteroids remain the cornerstone of postdiagnostic treatment.^15,16 For instance, Elias et al. reported significant clinical improvement, including the resolution of abducens and facial nerve palsies, following subtotal resection and high-dose corticosteroid therapy, although the patient’s sensorineural hearing loss was permanent.¹⁰ Similarly, Wani et al. noted symptom resolution and an unremarkable postoperative course following a subtotal decompression.¹³ On the other hand, some cases can be refractory to medical management. Crawford et al. described a patient with bilateral isolated CPA NS in which one tumor failed to respond to a combination of corticosteroids, azathioprine, and rituximab; this refractory lesion ultimately necessitated a second resection, which then successfully resulted in complete symptom resolution.⁵ These documented outcomes highlight that while upfront aggressive surgery should generally be avoided to prevent morbidity, surgical intervention remains a crucial and viable option for lesions causing progressive symptoms or those unresponsive to maximum medical and immunosuppressive therapies. A summary of previously reported cases of isolated CPA NS highlighted in the literature, alongside our present case, is provided in Table 1.

TABLE 1.

Summary of reported cases of CPA NS

Authors & Year	Age (yrs)/Sex	Presenting Symptoms	Systemic or Isolated	Treatment	Outcome
Clark et al., 198512	42/F	Hearing loss, tinnitus, dizziness, headaches, lt-sided fasciculations	Isolated	Subtotal resection followed by corticosteroids	Resolution of symptoms w/ follow-up date unspecified
Souliere et al., 199115	24/M	Hearing loss, tinnitus, dizziness, night sweats	Systemic	Corticosteroids	Resolution of symptoms at 48 mos
Souliere et al., 199115	28/F	Hearing loss, tinnitus	Systemic	Corticosteroids	Resolution of symptoms at 24 mos
Lipper et al., 199811	42/F	Hearing loss, tinnitus, dizziness, nausea, gastric fullness	Isolated	Partial resection	Histological diagnosis made postresection; long-term outcome not reported
Elias et al., 199910	42/F	Hearing loss, dizziness, headache, facial numbness, nausea	Isolated	Subtotal resection followed by high-dose corticosteroids	Resolution of abducens & facial nerve palsies; permanent unilat sensorineural hearing loss
Wani et al., 199913	38/M	Hearing loss, bitemporal headaches, horizontal diplopia, abducens palsy	Isolated	Subtotal decompression	Unremarkable postop course; resolution of symptoms
Sugisaki et al., 200016	56/F	Hearing loss, tinnitus	Systemic	Corticosteroids	Resolution of symptoms at 36 mos
Markert et al., 200714	40/F	Hearing loss, dizziness, headache, ataxia	Isolated	Biopsy followed by corticosteroids	Resolution of symptoms at 12 mos
Crawford et al., 20195	62/F	Hearing loss, progressive dizziness, facial numbness (bilat tumors)	Isolated	Bilat resections, corticosteroids, azathioprine, rituximab	Resolution of symptoms at 6 mos
Present case	25/M	Progressive diplopia, lt-sided hearing loss	Isolated	Open biopsy, high-dose corticosteroids	Good recovery, stable condition w/o new neurological deficits

Moreover, in a large series of 305 patients with NS, approximately 17% demonstrated nodular dural lesions that could mimic skull base tumors, and rare cases of bilateral internal auditory canal involvement were noted.¹⁷ These observations underscore that, although NS can present as skull base mass lesions, such presentations remain uncommon.

Imaging findings are frequently insufficient to distinguish NS from more prevalent CPA neoplasms. Dural attachment, T2 hypointensity, and homogeneous enhancement on MRI are classically associated with meningioma.^6,18 In scenarios in which conventional imaging is inconclusive, advanced nuclear medicine imaging, particularly 68Ga-DOTATOC or 68Ga-DOTATATE PET/CT, can be highly valuable. Meningiomas overexpress somatostatin receptor subtype 2, and 68Ga-DOTA-SSTR PET imaging provides superior diagnostic accuracy in differentiating meningiomas from other intracranial lesions compared to standard MRI.¹⁹ Recent studies have emphasized that such nuclear imaging modalities are crucial in identifying microscopic disease or incidentalomas and significantly altering patient management strategies.^20,21 In diagnostically challenging cases like ours, utilizing 68Ga-DOTATOC PET/CT could critically guide clinical decision-making, potentially avoiding unnecessary extensive resections and safely limiting the intervention to a targeted biopsy. In our patient, radiographic features suggested neoplasm, whereas CSF analysis and cervical lymph node biopsy were nondiagnostic. Therefore, tissue confirmation via surgical biopsy is pivotal for diagnostic certainty and appropriate treatment.

Histopathological analysis remains the gold standard for diagnosing NS. Under published consensus criteria, “definite” NS requires identification of noncaseating granulomas within CNS tissue in a compatible clinical context and following exclusion of alternative etiologies.⁷ Accordingly, granulomatous infections, other inflammatory disorders, and neoplastic mimics must be ruled out before confirming the diagnosis.

The primary strength of this case report lies in its documentation of an exceedingly rare presentation of NS confined to the CPA, a region where vestibular schwannomas and meningiomas are far more prevalent. By illustrating a scenario in which radiological findings strongly mimicked a meningioma, this report provides a crucial clinical lesson regarding the necessity of histopathological confirmation via biopsy to avoid the morbidity of unnecessary extensive resection. Additionally, the diagnosis was robustly supported by the exclusion of key mimics, including Langerhans cell histiocytosis and lymphoma, through comprehensive immunohistochemical analysis. However, this study is subject to the inherent limitations of a single-case design, which precludes the generalization of treatment outcomes to broader patient cohorts. Furthermore, while the immediate response to high-dose corticosteroids was favorable, the report is limited by the absence of long-term follow-up data to assess the durability of remission and the potential need for steroid-sparing agents over time.

Lessons

Following diagnosis, timely initiation of appropriate medical therapy is critical to prevent unwarranted aggressive surgical management. High-dose corticosteroids remain the first-line treatment for NS and are often associated with substantial clinical improvement.¹ Consistent with previously reported cases, serial contrast-enhanced MRI remains the imaging modality of choice for follow-up, typically obtained at 3- to 6-month intervals to accurately assess the efficacy of conservative management. In patients with an inadequate response to corticosteroids or an anticipated need for prolonged treatment, steroid-sparing immunosuppressive therapy and tumor necrosis factor alpha inhibitors may be used.²² Recent expert consensus guidance highlights the importance of individualized, multidisciplinary management of NS, commonly requiring close collaboration among neurology, rheumatology, and neurosurgical teams.²³ In the present case, prioritizing subtotal resection over gross-total resection was critical. Tissue confirmation established the diagnosis and facilitated medical management, thereby mitigating the potential morbidity of an unnecessary extensive resection.

Collectively, these findings underscore the importance of including NS in the differential diagnosis of unusual CPA lesions and of obtaining histopathological confirmation when the diagnosis remains uncertain.

Acknowledgments

We used ChatGPT version 5.2 for proofreading.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Peker, Duzkalir. Acquisition of data: all authors. Analysis and interpretation of data: Peker, Duzkalir. Drafting the article: Karaman. Critically revising the article: all authors. Reviewed submitted version of manuscript: Peker, Karaman, Duzkalir. Approved the final version of the manuscript on behalf of all authors: Peker. Study supervision: Peker, Kulac.

Correspondence

Selcuk Peker: Koc University Hospital, Istanbul, Turkey. peker@selcukpeker.com.