Final diagnosis:

Calcifying pseudoneoplasm of the neuraxis (CAPNON)

Discussion:

Calcifying pseudoneoplasm of the neuraxis (CAPNON) is a rare, benign, non-neoplastic fibro-osseous lesion that can occur anywhere along the central nervous system (brain and spine). It is considered a reactive rather than neoplastic process, though its exact etiology remains incompletely understood.

CAPNON affects both adults and children without sex predilection, with 150 cases reported in the literature. Common presenting symptoms include headache, seizures, radiculopathy, myelopathy, or neck/facial pain depending on location. Some cases are discovered incidentally.

The radiological appearance is nonspecific but has these characteristic features: CT: Densely calcified mass, MRI: T1 and T2 hypointense signal with minimal to no contrast enhancement (though mild rim or internal enhancement can occur), Well-circumscribed margins, smooth in smaller lesions and lobulated in larger ones. These features can mimic such important differential diagnoses as calcified meningiomas, oligodendrogliomas, chondrosarcomas, or vascular malformations.

The histomorphological features include a chondromyxoid fibrillary matrix with dense calcification, which can show nodular, interlacing linear ("chicken footprint"), or amorphous patterns. Additional features include palisading spindle or epithelioid cells, fibrous stroma, osseous metaplasia, psammoma bodies, multinucleated giant cells, and foreign body reaction

Surgical resection is the standard treatment for symptomatic lesions, with gross total resection being curative in the vast majority of cases. Recurrence is rare (~6–8%) even after incomplete resection. No deaths directly attributable to CAPNON have been reported. Asymptomatic or incidental lesions can be monitored with serial imaging.

References

  1. New insights into calcifying pseudoneoplasm of the neuraxis (CAPNON): a 20‐year radiological–pathological study of 37 cases. Histopathology. 2020. Ho ML, Eschbacher KL, Paolini MA, Raghunathan A.
  2. Calcifying Pseudoneoplasm of the Neuraxis: An Institutional Series of Ten Cases and Review of the Literature to Date. World Neurosurgery. 2023. Riviere-Cazaux C, Carlstrom LP, Eschbacher KL, et al.
  3. Calcifying Pseudoneoplasms of the Neuraxis (CAPNON) in Foramen Magnum (Cervicomedullary Junction) Region: A Case Report and Review of the Literature. British Journal of Neurosurgery. 2024. Atallah O, Kurian KM, Teo M.New
  4. Spinal Calcifying Pseudoneoplasm of the Neuraxis (CAPNON) Associated With Facet Joint Pathologies: CAPNON Diagnostic and Pathogenic Insights. Human Pathology. 2024. Fareez F, Yahya S, Fong C, et al.
  5. Calcifying Pseudoneoplasms of the Neuraxis: Report on Four Cases and Review of the Literature. Clinical Neurology and Neurosurgery. 2016. García Duque S, Medina Lopez D, Ortiz de Méndivil A, Diamantopoulos Fernández J.
  6. Skull Base Calcifying Pseudoneoplasms of the Neuraxis: Two Case Reports and a Systematic Review of the Literature. The Canadian Journal of Neurological Sciences. Le Journal Canadien Des Sciences Neurologiques. 2020.Yang K, Reddy K, Ellenbogen Y, et al.
  7. Incidental Multifocal Calcifying Pseudoneoplasm of the Neuraxis: Case Report and Literature Review. British Journal of Neurosurgery. 2023. Lu JQ, Yang K, Reddy KKV, Wang BH.
  8.  Calcifying Pseudoneoplasms of the Neuraxis: CT, MR Imaging, and Histologic Features. AJNR. American Journal of Neuroradiology. 2009. Aiken AH, Akgun H, Tihan T, Barbaro N, Glastonbury C.
  9. Calcified Pseudoneoplasm of the Neuraxis. AJNR. American Journal of Neuroradiology. 2021. Benson JC, Trejo-Lopez J, Boland-Froemming J, et al.
  10. Calcifying Pseudoneoplasms of the Neuraxis (CAPNON). A Case Report. Neuropathology: Official Journal of the Japanese Society of Neuropathology. 2021. Li WQ, Wang SH, Zhang ZW, et al.
  11. Spinal Calcifying Pseudoneoplasm of the Neuraxis (CAPNON) and CAPNON-like Lesions: CAPNON Overlapping With Calcified Synovial Cysts. Pathology. 2022. Lu JQ, Al Mohammadi WJB, Fong C, et al.