Calcifying pseudoneoplasm of the neuraxis (CAPNON): Unraveling a rare non-neoplastic calcified central nervous system lesion

Abstract

Introduction and importance

Calcifying pseudoneoplasms of the neuraxis (CAPNON) are infrequent benign brain tumors. They demonstrate slow growth and are characterized by calcium deposits within the tumor tissue. CAPNONs are observed in the supratentorial compartment of the brain. Due to their rarity, increasing knowledge of CAPNONs is essential for accurate diagnosis and effective management of affected patients. This report describes a case of CAPNON diagnosed in a 56-year-old female and discusses the clinical, imaging, and histopathological findings of this rare entity.

Case presentation

A 56-year-old female presented with a history of recurrent holocranial headache and dizziness, progressively worsening over the last month. Physical and neurological examinations revealed no evident abnormalities. Brain magnetic resonance imaging revealed a calcified and cystic mass, measuring 40 × 32 mm in the right frontal lobe. Complete excision of the mass was done. Histologically, the lesion was composed of glial tissue with abundant amorphous lamellar calcification and a myxoid matrix in the background. Concentric circular calcifications were observed with osseous metaplasia present in some areas. Palisading spindle to epithelioid cells was noted around the lesion. The final diagnosis was CAPNON. The postoperative course was uneventful, and one year of follow-up revealed no signs of recurrence.

Discussion

CAPNON typically occurs in middle-aged adults and can present with variable symptoms depending on its location within the brain, including seizures, headaches, or neurological deficits. Surgical resection is considered the optimal treatment for CAPNON. Raising awareness and understanding of this rare entity is necessary for accurate diagnosis and management of patients affected by this condition.

Highlights

• •Calcifying pseudoneoplasms of the neuraxis (CAPNON) is a rare benign brain tumor
• •The diagnosis is made on histopathological examination of resected tissue
• •Increased awareness and understanding of this rare entity is important for accurate diagnosis and management of patients with this condition

1. Introduction

Calcifying pseudoneoplasms of the neuraxis (CAPNON) represent uncommon and benign brain tumors, with a reported incidence of merely 150 cases, often leading to misdiagnosis as more prevalent brain tumors [1]. Although the exact etiology of CAPNON remains uncertain, it is postulated to be a reaction to various factors, including trauma, infection, inflammation, and neoplasms, primarily due to its benign clinical behavior and histopathological characteristics [2]. These lesions are also known as fibro-osseous CNS lesions and typically demonstrate slow growth, characterized by the presence of calcium deposits within the tumor tissue, resulting in distinctive features on imaging studies. CAPNONs are predominantly found in the supratentorial region of the brain [1]. Despite their rarity, raising awareness and knowledge regarding CAPNONs is crucial for the accurate diagnosis and effective management of patients affected by this condition. In this study, we present a case of CAPNON diagnosed in a 56-year-old female and extensively discuss the clinical, imaging, and histopathological findings associated with this exceptional pathological entity.

2. Case presentation

A 56-year-old female presented with a 2-year history of recurrent holocranial headache and dizziness, which had worsened in the preceding month. Physical and neurological examinations revealed no obvious abnormalities. Axial T2-weighted Magnetic resonance imaging (MRI) sequence showed a multilobulated calcified mass on the right frontal lobe, surrounded by edema and associated with a cystic cavity in the anterior region, measuring 40 × 32 mm (Fig. 1). The imaging differentials initially included an oligodendroglioma. A frontal craniotomy was performed, and the entire mass was excised, after which it was sent for histopathological and immunohistochemical analysis. Grossly, the lesion measured 2.5 cm and appeared homogeneous, with calcified areas but without identifiable compartments. Microscopic examination revealed glial tissue containing amorphous lamellar calcification with a chondromyxoid matrix in the background. The calcifications exhibited a concentric circular structure, and some areas of ossification were observed. Additionally, peripheral palisading spindle to epithelioid cells were seen around the lesion (Fig. 2). These findings were consistent with the diagnosis of CAPNON. The postoperative course was uneventful, and the patient has been under observation for one year following the surgical intervention with no signs of recurrence observed in either clinical or radiological assessments.

Fig. 1.

Axial T2-weighted Magnetic resonance imaging (MRI) sequence showed a multilobulated calcified mass on the right frontal lobe, surrounded by edema and associated with a cystic cavity in the anterior region.

Fig. 2.

H&E (×400 magnification). A/ The lesion consisted of glial tissue containing amorphous lamellar calcification with chondromyxoid matrix in the background. The calcifications had concentric circular structure. B/ Some areas of ossification were noticed.

The work has been reported in line with the SCARE 2020 criteria [3].

3. Discussion

CAPNON is an uncommon and benign tumor that can arise anywhere in the neuraxis, affecting both children and adults, with a higher incidence in males [4]. It can be diagnosed at any age, ranging from 2 to 90 years [4]. Typical symptoms associated with these tumors include headaches, seizures, and focal neurological issues. However, the specific clinical presentation may vary based on factors like the tumor's location, size, and its impact on surrounding tissues [5].

Imaging techniques play a crucial role in diagnosing central nervous system (CNS) tumors, aiding in characterizing CAPNON and differentiating it from other calcified CNS lesions. On conventional radiography and computed tomography, CAPNONs usually appear as solid lesions with complete or peripheral calcifications. When imaged using MRI, CAPNONs typically exhibit low-intensity signals in both T1- and T2-weighted sequences, with minimal or no contrast enhancement, and they do not cause surrounding vasogenic edema [6,7].

Despite these characteristic imaging features, the radiological diagnosis of CAPNONs may not always be straightforward, as they can share similar imaging traits with more common calcified lesions. In cases where CAPNONs are located in the skull base, they may resemble intra-axial calcified lesions like low-grade glial neoplasms (e.g., oligodendroglioma, ependymoma), mixed neuronal-glial tumors (e.g., ganglioglioma), vascular malformations (e.g., cavernous malformation), and granulomatous or infectious processes (e.g., tuberculosis). In the present case, the tumor was initially suspected to be an oligodendroglioma.

The definitive diagnosis of CAPNON relies on histopathological examination, revealing nodular patterns composed of a chondromyxoid matrix containing fine calcifications with psammomatous bodies. These nodules are surrounded by epithelioid and spindle cells at the periphery. A foreign body reaction with multinucleated giant cells is also observed [4,8]. However, the presence of these components may vary among reported cases, and in some instances, the classic histopathological characteristics may be absent, making differential diagnosis challenging. In such cases, the differential diagnosis may include infectious granulomatous diseases, foreign body reaction, and neoplasms like chordomas, chondroblastomas, chondrosarcomas, and metaplastic meningioma [4,9]. Immunohistochemical analysis commonly shows that the palisading cells express epithelial membrane antigen (EMA) and vimentin but are negative for glial fibrillary acid protein, S-100 protein, and smooth muscle actin [8]. EMA may be helpful in distinguishing CAPNONs from calcified psammomatous and metaplastic meningiomas, as CAPNONs usually exhibit irregular EMA expression confined linearly to the periphery of the chondromyxoid matrix, unlike meningiomas, which show widespread positive EMA expression [9].

The management of CAPNONs depends on their location, size, and presenting symptoms. Asymptomatic lesions may be observed without intervention [4]. Surgically resecting superficially located intracranial lesions is more likely. Patients who undergo surgical resection of intracranial CAPNONs typically remain stable or experience an improvement in symptoms after the surgery [6]. Although data on surgical treatment is limited, achieving complete and safe resection, when possible, should be the primary objective to achieve optimal clinical outcomes [10]. In our case, the patient underwent tumor excision and showed no signs of recurrence after one year of follow-up.

The prognosis of CAPNONs primarily depends on their location and size, with clinical symptoms arising from the mass effect of the tumor rather than its pathological nature [4]. Overall, the outlook for CAPNON is considered positive due to its benign and non-neoplastic nature, regardless of the extent of resection, and the infrequent recurrence [4].

4. Conclusion

In conclusion, this case report highlights the challenges in diagnosing CAPNON radiologically, as it can mimic other brain tumors such as oligodendroglioma. Accurate diagnosis of CAPNON requires histopathological examination, and complete surgical resection, if feasible, is the recommended treatment approach. The prognosis for CAPNON is favorable due to its benign nature and low recurrence rate.

Ethical approval

We respected ethical considerations in our work. Rabta hospital's ethic committee approval number is RH/12 dated 3rd January 2023.

Sources of funding

No.

CRediT authorship contribution statement

All the authors read and approved the final version of the manuscript.

Farah Sassi (MD): conception, acquisition of data, literature research and preparing the manuscript

Alia Zehani (MD): acquisition of clinical data, revising the manuscript

Khalil ghedira (MD): Supervision and acquisition of clinical data.

Ines Chelly (MD): revising the manuscript

Khedija Bellil (MD): revising the manuscript

Slim Haouet (MD): Final approval of the version to be published.

Guarantor

Sassi Farah.

Consent

Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.

Provenance and peer review

Not commissioned, externally peer-reviewed.

Declaration of competing interest

The authors declare that they have no affiliations with or involvement in any organization or entity with any financial interest in the subject matter or materials discussed in this manuscript.

Data availability

All data generated or analysed during this study are included in this published article (and its supplementary information files).