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CC BY-NC-ND 4.0 · Asian J Neurosurg 2025; 20(03): 605-609
DOI: 10.1055/s-0045-1806859
Case Report

Recurrent Calcifying Pseudoneoplasm of the Neuraxis in Meckel's Cave with Cyst Extending into the Cerebellopontine Cistern after Resection of the Cystic Component: A Case Report

Ryuta Yamada
1   Department of Neurosurgery, Asahi University Hospital, Gifu, Japan
,
Hiroki Kobayashi
1   Department of Neurosurgery, Asahi University Hospital, Gifu, Japan
,
Yuichi Nomura
1   Department of Neurosurgery, Asahi University Hospital, Gifu, Japan
,
Naoki Oka
1   Department of Neurosurgery, Asahi University Hospital, Gifu, Japan
,
Jouji Kokuzawa
1   Department of Neurosurgery, Asahi University Hospital, Gifu, Japan
,
Yasuhiko Kaku
1   Department of Neurosurgery, Asahi University Hospital, Gifu, Japan
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Abstract

Calcifying pseudoneoplasms of the neuraxis (CAPNON) are rare non-neoplastic calcified lesions that can occur throughout the entire neuraxis. Cranial nerves may be involved in skull base lesions. Surgical resection usually has a good prognosis, with only a few cases of recurrence reported in the relevant literature. We experienced a recurrent case of CAPNON in Meckel's cave extending to the cerebellopontine cistern with involvement of the trigeminal nerve after initial resection of the cystic part of the lesion. A 48-year-old man presented with a 4-year history of right-sided ptosis. Magnetic resonance imaging revealed a calcified lesion arising in Meckel's cave, with a cystic lesion extending to the cerebellopontine cistern. The cystic part of the lesion was excised during the initial surgery using the right lateral suboccipital approach. However, the cystic lesion regrew to its preoperative size within 23 months. The right extradural subtemporal approach was used to successfully remove both the calcified mass in the right Meckel cave and the cystic lesion extending to the right cerebellopontine cistern during the resection of the lesion. The patient's neurological symptoms resolved postoperatively. CAPNON was identified during the histopathological examination. This report describes a rare case of CAPNON in Meckel's cave with a unique clinical course. After the first operation, cystic lesions recurred in the cerebellopontine cistern, but they were successfully treated by a second operation.


 

Keywords

calcifying pseudoneoplasms of the neuraxis - CAPNON - Meckel's cave - Cyst

Introduction

Calcifying pseudoneoplasms of the neuraxis (CAPNON) are rare, non-neoplastic, calcified lesions that were first described by Rhodes and Davis in 1978 as an unusual fibro-osseous component in intracranial lesions.[1] They can occur anywhere in the central nervous system, including the brain and spine. These tumors can be either intra-axial or extra-axial. The clinical symptoms, including seizures, headache, and focal neurological deficits, are attributed to the local compression or irritation of adjacent tissue.[2] The etiology of CAPNON remains unclear, but it has been suggested that CAPNON may develop as a healing response to multiple triggering factors, such as trauma, infection, or inflammation.[3] Although there are no standard guidelines for its management, complete resection of the lesion can achieve a good prognosis without recurrence. We present a case of CAPNON of the Meckel cave involving the trigeminal nerve with a cyst extending into the cerebellopontine cistern, which recurred after resection of the cystic component.


 

Case Presentation

A 48-year-old man presented with a 4-year history of right-sided ptosis. He also had right facial numbness, and the transient right facial spasm resolved for several months. Magnetic resonance imaging (MRI) revealed a calcified mass in the right Meckel cave with a cyst extending to the right cerebellopontine cistern, compressing the midbrain and upper pons ([Fig. 1A]). The calcified mass in Meckel's cave was 15 × 15 mm in diameter ([Fig. 1B]), with mixed intensity signals on T1- and T2-weighted images with peripheral enhancement ([Fig. 1C]). The cystic lesion of the cerebellopontine cistern was 10 × 13 mm in diameter with high-intensity signals on T2-weighted images without enhancement. Based on radiological examinations, the differential diagnoses included meningioma, trigeminal schwannoma, and fibro-osseous tumor.

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Fig. 1 (A) Axial T2-weighted MRI demonstrates a low-intensity mass in the right of Meckel's cave (arrow) connected to a cystic lesion in the cerebellopontine cistern (arrowhead). (B) Plain coronal CT demonstrating a calcified mass in the right of Meckel's cave. (C) Axial T1-weighted image with contrast enhancement demonstrating irregular rim enhancement of the mass in the right of Meckel's cave.

An attempt was initially made to resolve the patient's ptosis by excising the cystic lesion located in the right cerebellopontine cistern, while the calcified mass in Meckel's cave was left untouched. Through right lateral suboccipital craniotomy, excision of the cystic lesion attached to the right trigeminal nerve and decompression of the oculomotor nerve could be achieved ([Fig. 2A, B]). The patient had an uneventful postoperative course and his right ptosis improved. A histopathological examination revealed connective tissue without any signs of a neoplasm. Postoperative MRI showed that the cystic lesion in the right cerebellopontine cistern was fully removed ([Fig. 3A]). However, within the next 23 months, the cystic lesion grew back to its preoperative level ([Fig. 3B]). The patient had a recurrence of right ptosis and right trigeminal neuralgia affecting the V1 and V2 territories. Resection of the lesion, including the calcified mass in the right Meckel cave and the cystic lesion extending to the right cerebellopontine cistern, was planned through a right extradural subtemporal approach 27 months after the initial surgery. The calcified mass in Meckel's cave could be extirpated with the preservation of the compressed right trigeminal nerve. The tentorial incisura ([Fig. 3C, D]) was cut to remove the cystic lesion connecting to the calcified mass in Meckel's cave. The patient's postoperative course was uneventful, and his right ptosis and trigeminal neuralgia resolved. Postoperative MRI showed complete resection of both the calcified mass and the cystic lesion ([Fig. 3C]), with no recurrence at 10 months after the procedure.

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Fig. 2 (A) Operative view in the first operation demonstrating the cystic lesion in the right cerebellopontine cistern attaching with the trigeminal nerve. (B) Operative view of the first operation after extirpation of the cystic mass. The arrowhead indicates the right trigeminal nerve. The double arrow indicates the cochlear nerve. The arrow indicates the basilar artery. (C) Operative view in the second operation demonstrating a calcified mass in the right Meckel cave (arrow) through a right extradural subtemporal approach. (D) Operative view in the second operation demonstrating total extirpation of the calcified mass in the right of Meckel's cave and a cystic lesion in the cerebellopontine cistern with preservation of the trigeminal nerve (arrow).
Zoom
Fig. 3 (A) T2-weighted MRI obtained after the initial operation shows that the cystic lesion in the right cerebellopontine cistern was removed, while the low-intensity mass in the Meckel cave remained. (B) T2-weighted MRI obtained 23 months after the initial operation demonstrating recurrence of the cystic lesion in the right cerebellopontine cistern (arrow) with a low-intensity mass in Meckel's cave (arrowhead). (C) T2-weighted MR image obtained after the second operation demonstrating removal of both the low-intensity mass in Meckel's cave and the cystic lesion in the right cerebellopontine cistern with preservation of the trigeminal nerve (arrow).

 

Histopathological Findings

The histopathological examination found calcified fibrillary material cores, which were surrounded by spindled epithelioid cells and fibrovascular tissue containing lymphocytes. Calcified material was often arranged in a linear pattern and contiguous with spindled cells and fibrous connective tissue ([Fig. 4A]). Immunohistochemical staining revealed focally scattered epithelial membrane antigen (EMA) positive peripheral spindled epithelioid cells ([Fig. 4B]).

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Fig. 4 (A) Hematoxylin and eosin staining demonstrating cores of calcified, fibrillary materials surrounded by spindled to epithelioid cells and fibrovascular tissue containing lymphocytes. (B) Some peripheral spindled to epithelioid cells demonstrating positive epithelial membrane antigen (EMA) immunostaining.

 

Discussion

CAPNON are non-neoplastic and uncommon, can occur throughout the neuraxis, and affect both children and adults aged 2 to 90 years.[4] Intracranial CAPNON is associated with a relatively higher incidence of intra-axial and supratentorial lesions.[5] [6] The lesions seem to be slow growing, and the presenting symptoms tend to be related to local compression or irritation of adjacent tissues. Seizures, followed by headaches, are the most common symptoms of intracranial CAPNON.[2] When CAPNON are located in the skull base, cranial neuropathy may also be present as a result of compression and involvement.[7] [8] [9] [10] [11] [12] [13] [14] [15] Yang et al[13] reviewed 24 CAPNON cases located at the skull base and identified a high incidence (45.8%) of cranial neuropathy, likely due to the adherence of CAPNON to the cranial nerves. Garen et al[7] reported a case of CAPNON in Meckel's cave presenting with a 6-year history of atypical right facial pain that resolved following resection of the lesion.

Radiological findings are nonspecific and reflect heavy calcifications. CT shows solid attenuated calcifications, and MRI often shows a well-demarcated lesion that is uniformly hypointense on both T1- and T2-weighted images.[2] [3] Contrast enhancement often shows minimal internal or rim enhancement but can be more prominent in the setting of inflammatory changes and aggressive growth.[16] Surrounding brain edema has been reported in some cases[2] [17] [18] [19] but is usually absent. Contiguous cystic lesions with calcified lesions have been reported in some cases.[17] [19] [20] [21] Intracranial CAPNON should be differentiated from calcified meningiomas, chordoma, chordosarcoma, schwannoma, cavernous malformation, and other inflammatory lesions.[3] [22] [23] Meningiomas typically show isointensity on T1-weighted images and have mixed hypo- and hyperintensity on T2-weighted images of MRI, and have homogeneous gadolinium enhancement. Chordoma, chordosarcoma, and schwannoma typically show very high signal on T2-weighted images. CAPNON typically have heavily calcified lesions that show uniform hypointensity on T1- and T2-weighted images of MRI, and minimal linear rim or serpiginous internal enhancement with or without minimal surrounding edema. Despite these characteristic imaging features, radiological diagnoses of CAPNON are not always easy to make without surgical specimen.

The “classic” histopathological features of CAPNON include a distinctive set of common elements: (1) a chondromyxoid matrix with a nodular pattern; (2) palisading spindles to epithelioid cells; (3) varying amounts of fibrous stroma; (4) calcification, osseous metaplasia, and scattered psammoma bodies; and (5) foreign body reaction with giant cells.[24] Although not all cases of CAPNON exhibit these histopathological features, the combination of their presence can lead to a diagnosis of CAPNON. An immunohistochemical analysis is useful for diagnosing CAPNON. Palisading cells are usually positive for EMA and vimentin but are negative for glial fibrillary acid protein (GFAP), S-100 protein, and smooth muscle actin.[25] EMA is the most effective way to distinguish CAPNON from calcified psammomatous and metaplastic meningioma. Meningiomas are widely positive for the expression of EMA, whereas the expression of EMA is limited in CAPNON. This is confirmed linearly to the periphery of the chondromyxoid matrix.[26] It has been speculated that CAPNON expresses EMA only when the meninges are involved and that EMA positivity is limited to meningeal cells entrapped in CAPNON lesions.[13]

Although the etiology of CAPNON remains unclear, it has been speculated that they may form as part of a reactive process related to inflammation or injury, and some studies support this theory.[4] [16] Yang et al[25] revealed evidence for this theory, including the aggregation of a neurofilament light chain protein (NF-L), a marker of axonal injury, in all lesion cores, and variable infiltration of CD8+ T cells with a decreased CD4+/CD8+ T-cell ratio in cellular areas. Thus, the cores of CAPNON might be formed by the aggregation of tissue debris containing NF-L from damaged axons, which would then calcify or ossify over time and attract a chronic reactive outer layer consisting of various cells, such as spindled fibroblasts, with variable fibrosis and activated macrophages, including multinucleated giant cells.[25]

The treatment of CAPNON depends on factors such as the location, size, and presentation of the signs and symptoms. Asymptomatic lesions can be conservatively managed. In cases of symptomatic or growing lesions, total resection is considered the standard of care if technically feasible. Surgical resection has been attempted in most cases for symptomatic lesions in the skull base, but the extent of resection may be limited by the firm, calcified nature and its adherence to cranial nerves.[9] [10] [13] [22] It has been suggested that cranial neuropathies may not completely resolve, even after gross total resection.[13] Five cases of recurrent intracranial CAPNON have been reported.[4] [8] [18] [21] [27] Four patients experienced recurrence after subtotal resection, whereas one patient experienced recurrence after gross total resection.[27] In all cases, recurrent CAPNON developed in the original location. The clinical course of the present case may be unique. The cystic component extending to the cerebellopontine cistern recurred 23 months after the initial surgery, which resected only the cystic part. Subsequent total resection of the lesion including the calcified mass in Meckel's cave and the cystic component extending to the cerebellopontine cistern through a single surgical corridor could achieve good clinical course without recurrence. As the cystic component might be a reactive substance of the core of CAPNON in Meckel's cave, recurrence of the lesion might be unavoidable without resection of the core of CAPNON. Resecting both the calcified mass and the cystic lesion should be mandatory.


 

Conclusion

The authors reported a case of CAPNON in Meckel's cave with a unique clinical course in which the recurrence of a cystic lesion in the cerebellopontine cistern following the first operation was resolved by the second operation, resecting both the calcified mass and the cystic lesion.


 

 

Conflict of Interest

None declared.


Address for correspondence

Ryuta Yamada, MD
Department of Neurosurgery, Asahi University Hospital
Gifu 500-8856
Japan   

Publikationsverlauf

Artikel online veröffentlicht:
25. März 2025

© 2025. Asian Congress of Neurological Surgeons. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/)

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Zoom
Fig. 1 (A) Axial T2-weighted MRI demonstrates a low-intensity mass in the right of Meckel's cave (arrow) connected to a cystic lesion in the cerebellopontine cistern (arrowhead). (B) Plain coronal CT demonstrating a calcified mass in the right of Meckel's cave. (C) Axial T1-weighted image with contrast enhancement demonstrating irregular rim enhancement of the mass in the right of Meckel's cave.
Zoom
Fig. 2 (A) Operative view in the first operation demonstrating the cystic lesion in the right cerebellopontine cistern attaching with the trigeminal nerve. (B) Operative view of the first operation after extirpation of the cystic mass. The arrowhead indicates the right trigeminal nerve. The double arrow indicates the cochlear nerve. The arrow indicates the basilar artery. (C) Operative view in the second operation demonstrating a calcified mass in the right Meckel cave (arrow) through a right extradural subtemporal approach. (D) Operative view in the second operation demonstrating total extirpation of the calcified mass in the right of Meckel's cave and a cystic lesion in the cerebellopontine cistern with preservation of the trigeminal nerve (arrow).
Zoom
Fig. 3 (A) T2-weighted MRI obtained after the initial operation shows that the cystic lesion in the right cerebellopontine cistern was removed, while the low-intensity mass in the Meckel cave remained. (B) T2-weighted MRI obtained 23 months after the initial operation demonstrating recurrence of the cystic lesion in the right cerebellopontine cistern (arrow) with a low-intensity mass in Meckel's cave (arrowhead). (C) T2-weighted MR image obtained after the second operation demonstrating removal of both the low-intensity mass in Meckel's cave and the cystic lesion in the right cerebellopontine cistern with preservation of the trigeminal nerve (arrow).
Zoom
Fig. 4 (A) Hematoxylin and eosin staining demonstrating cores of calcified, fibrillary materials surrounded by spindled to epithelioid cells and fibrovascular tissue containing lymphocytes. (B) Some peripheral spindled to epithelioid cells demonstrating positive epithelial membrane antigen (EMA) immunostaining.