Calcifying pseudoneoplasms of the neuraxis (CAPNON) are very rare, non-neoplastic, calcified lesions of the central nervous system of poorly understood etiology.
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Epidemiology
Given the rarity of these lesions, detailed epidemiological data is not available. Since their first description, less than 50 cases have been reported in the literature.
Clinical presentation
The clinical presentation of patients with CAPNON is heterogeneous and generally depends on the location and size of the lesion. Symptoms are related to local compression or irritation of the adjacent tissue. In spinal disease, the predominant presentation is local or back pain 2.
By contrast, intracranial CAPNON may present with not only headache but also seizures, cranial neuropathy, or motor deficits 2. In a few cases, it was an incidental finding 2.
Pathology
CAPNONs are usually solitary extra-axial, or less frequently intra-axial, masses 1-4. An understanding of etiology remains elusive with reactive, metaplastic and even neoplastic processes having been proposed 3,5.
They demonstrate extensive calcifications and a nodular chondromyxoid matrix with an amorphous quality and fibrovascular stroma. The spindle and epithelioid cells surrounding the matrix showed positive staining with antibodies against epithelial membrane antigen (EMA) 1-3. They are S100 and GFAP negative 3.
Although the typical histopathologic features can be observed in most cases, some may be unusual and may be confused with calcified meningioma or tumoral calcinosis.
Radiographic features
CT
Calcifying pseudoneoplasm of the neuraxis may present as a heavily calcified well-defined leptomeningeal or parenchymal mass.
MRI
Typical signal characteristics of a calcifying pseudoneoplasm of the neuraxis are those of calcium:
- T1: iso to hypointense
- T2: low signal on FLAIR and T2
- T1 C+ (Gd): varies from none to moderate enhancement
- T2*: mild blooming
Treatment and prognosis
Resection of a CAPNON is usually curative. Morbidity relates to operative complications and damage to structures adjacent to the mass 3,4.
History and etymology
Calcifying pseudoneoplasm of the neuraxis was first described by Rhodes and Davis in 1978 6.
Differential diagnosis
CAPNON should be considered in the imaging differential diagnosis of a heavily calcified lesion in the CNS and the differential will depend on the location. It is worth considering this entity to avoid aggressive surgical intervention in a lesion that is difficult to resect, as the natural history of CAPNON is generally indolent.
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