Calcifying pseudoneoplasms of the neuraxis: CT, MR imaging, and histologic features

Abstract

Background and purpose: Non-neoplastic, calcified, fibro-osseous lesions known as "calcifying pseudoneoplasms of the neuraxis" (CAPNON) are rare and can occur anywhere within the neuraxis. The radiologic and histopathologic characteristics of this unusual entity are not well understood. We present the largest series reviewing the MR imaging features of CAPNON.

Materials and methods: The MR and CT imaging features in 4 patients with a pathologic diagnosis of "calcifying pseudoneoplasms of the neuraxis" were retrospectively reviewed. A neuropathologist also analyzed the histopathologic features for typical and atypical patterns.

Results: Imaging features were strikingly similar for all 4 patients. All lesions appeared T1 and T2 hypointense without vasogenic edema. All tumors had dense calcification, and 3 tumors showed minimal linear internal or rim enhancement on MR imaging.

Conclusions: CAPNON may mimic more common vascular malformations or neoplasms and are often not considered in the differential diagnosis of calcified lesions. CAPNON should be included in the differential diagnosis of a calcified mass with marked T1 and T2 hypointensity and limited to no enhancement. Careful CT and MR imaging evaluation can suggest this entity, and this preoperative recognition may help subsequent management decisions.

Fig 1.

Typical radiologic features of extra-axial CAPNON. A, Noncontrast CT scan shows a densely calcified mass in the right temporal horn. B, Axial T2-weighted MR image shows a uniform T2 hypointense mass centered in the right temporal horn. C, Axial T1-weighted postgadolinium sequence illustrates marked T1 hypointensity with scattered linear areas of enhancement that correspond to the strands of T2 hyperintensity. This appearance was seen in both of our larger lesions and may correspond to the vascular stromal elements seen within these lesions.

Fig 2.

Typical radiologic features of intra-axial CAPNON. A, Noncontrast CT scan shows a left hippocampal mass with attenuated calcification. B, Coronal T2-weighted sequence demonstrates T2 hypointensity with a nodular border. C, Coronal T1-weighted sequence shows the typical T1 hypointensity. Preoperatively, this lesion was thought to represent a cavernous malformation. In retrospect, the nodular contour on T2 and lack of internal T2 hyperintensity would be atypical for a cavernous malformation of this size.

Fig 3.

Typical histopathologic features of CAPNON. A, The typical chondromyxoid matrix of CAPNON (H&E, original magnification ×100). B, Focal osseous metaplasia is seen in all 4 cases (H&E, original magnification ×100). C, Medium-power magnification of the chondromyxoid matrix and the peripheral spindle cells (H&E, original magnification ×200). D, Immunohistochemical analysis for EMA demonstrating positive staining in the spindle cells surrounding the matrix (EMA immunohistochemistry, original magnification ×200).

Fig 4.

Atypical and unusual features of CAPNON. A, Areas of coalescent concentric lamellar calcifications without intervening chondromyxoid matrix or cells (H&E, original magnification ×100). B, More basophilic amorphous lamellar calcifications without intervening chondromyxoid matrix and with rare meningothelial cells (H&E, original magnification ×100). C, Adjacent cortical region showing meningioangiomatosis (H&E, original magnification ×200). D, Surrounding parenchyma with prominent perivascular lymphocytic infiltrates and Rosenthal fibers (H&E, original magnification ×200).