Calcifying pseudoneoplasm of the neuraxis (CAPNON)
General description
Calcifying pseudoneoplasm of the neuraxis (CAPNON) represents a rare, benign, non-neoplastic fibro-osseous lesion of the central nervous system. CAPNON demonstrates no clear age or gender predilection, with cases reported across a wide age spectrum ranging from 2 to 90 years. The mean age at presentation has been reported as approximately 46 years, though some studies suggest the lesions are more commonly encountered in middle-aged adults.
References
- Aiken, A. H., et al. "Calcifying pseudoneoplasms of the neuraxis: CT, MR imaging, and histologic features." American journal of neuroradiology 30.6 (2009): 1256-1260.
- Greco, Elena, et al. "Calcifying pseudoneoplasms of the neuraxis (CAPNON): the great tumor mimicker." Radiology Case Reports 17.9 (2022): 3157-3161.
Calcified mass
CAPNONs can occur anywhere within the central nervous system and have been reported to arise in both the brain and spine with similar frequency. These lesions can be found both intra-axially and extra-axially. Intracranial lesions are most commonly supratentorial, with approximately 74% occurring in supratentorial locations and 26% in infratentorial regions. Within the skull base, CAPNONs are commonly extra-axial and often lie nestled within sulci or adjacent to the dura mater. Spinal CAPNONs occur throughout the spine but demonstrate a predilection for the lumbar region, followed by cervical and thoracic areas. The lesions can be intradural, extradural, or intradural extramedullary in location.
CAPNONs typically demonstrate well-defined, circumscribed margins. The lesions often appear as well-circumscribed masses with smooth or occasionally lobulated borders.
On CT imaging, CAPNONs characteristically present as densely calcified, well-circumscribed lesions. The calcifications appear as solid, peripherally distributed, or completely calcified masses.
CAPNONs demonstrate hypointense signal on T1-weighted sequences and T2-weighted sequences and FLAIR images due to the extensive calcification. This hypointensity is typically uniform and reflects the calcium content within the lesion. Enhancement characteristics are variable but typically minimal. When present, enhancement usually manifests as minimal linear internal or rim enhancement.
Vasogenic edema is characteristically absent or minimal in most CAPNONs. This lack of surrounding edema represents an important distinguishing feature from many neoplastic lesions.