A 33‐Year‐Old Male with Five Years of Neck Pain

Clinical History

A 33‐year‐old male patient reported on head and neck pain radiating into the left maxilla, that had already persisted for 5 years presented in the clinic, as he experienced an acute neuralgic pain provoked by physical activity (VAS 8/10 points) as a new symptom. MRI showed a left‐sided hypointense, polyglobulated tumor in the left cerebello‐pontine angle, with irregular contrast enhancement and hypointensity on T1 and T2 images (Figure 1a–c). The tumor exerted pressure on the medulla oblongata, resulting in perifocal edema. By cranial CT (Figure 1d) the tumor had a strong hyperdense signal. The patient complained of no other neurological deficits. The tumor was extirpated microneurosurgically using electro‐physiological monitoring via retromastoidal approach and semisitting position of the patient. Since the lesion was adjacent to the brain stem, a thin layer was left (intraoperative pictures of the tumor: Figure 1e, 1f). Postoperatively, the patient sustained a new facial and glossopharyngeal palsy, which considerably improved at 3 months’ follow‐up.

Figure 1.

Pathology

The tissue contained multiple pieces, grey white, soft to hard, measuring 8 x 8 x 8 mm. Histological examination showed amorphic tissue that was partly characterized by a lobulated appearance. At the periphery of the lobules cells with epithelioid appearance and a radial orientation, were seen (Figure 1g). Other areas had fibrohistiocytic tissue with multinucleated cells (Figure 1h). There was also fibro‐osseous metaplasia including osteoclasts and calcifications, surrounded by collagenous fibrovascular strands (Figure 1i). Adjacent central nervous tissue showed reactive gliosis. There was no necrosis. Immunostains were negative for MNF 116 (pancytokeratin), CK8, GFAP, Synaptophysin, S100 protein, actin, desmin, p53 and IDH‐1‐R132H mutation. A part of the epithelioid cell elements expressed EMA (Figure 1j) and KiM1P1 (a macrophage marker) (Figure 1k).

The Ki67 proliferation index in those cells was about 5% (Figure 1l). What is your diagnosis?

Diagnosis

Calcifying pseudoneoplasm of the neuraxis (CAPNON), located in the cerebellopontine angle. This is a rare, uncommon and pathogeneticly unexplained lesion. In the literature it is also described as "fibro‐osseous lesion", "cerebral calculi" or "brain stone".

Discussion

Calcifying pseudoneoplasms of the brain are rarely reported. Since the first reported case of a "Calculi within the brain" by Miller in 1929 3 less than 100 clinical cases have been described in the literature. These lesions are often located intracranially but may also be observed in the spinal cord. The age of patients with this diagnosis ranges from 6 to 83 years, with a mean age of 46 years. The histopathological background is not yet understood, but concerning the reported cases these lesions seems to be usually benign. It is discussed that they develop as a reactive response on unspecific stimulating factors rather than a neoplastic process 2.

Typical differential diagnosis of preoperative imaging, depending on location, is meningioma, chordoma or chondrosarcoma as well as vestibular schwannoma. The typical T1 and T2 hypointensity of calcifying pseudoneoplasm 1 would be unusual for the described entities, except meningioma. Further important differential considerations for calcified lesions should contain tumors like gangliogliomas, oligodendrogliomas, vascular malformations and infections such as tuberculosis 1, 2. Microscopically, the differential diagnosis includes several reactive lesions such as granulomatosis, chondroid chordoma, chondroma, chondrosarcoma, metaplastic meningioma or other calcified primary parenchymal central nervous system tumors 4.

Calcifying pseudoneoplasms present classic histopathological characteristics containing calcification, osseus metaplasia, chondromyxoid matrix, fibrous stroma, spindle or epithelioid cells and also foreign‐body reaction with giant cells. The characteristics are varying a lot, not all features must be present. The current immunohistochemical findings could not contribute to determine the etiology of the lesion. In reported cases the staining with GFAP and S‐100 was negative. EMA was positive in a part of epithelioid cell elements but can also be negative as reported in other cases.

Concluding calcifying pseudoneoplasm is a rare differential diagnosis for calcifying tumors of the neuraxis. Although complete surgical resection is recommended even an incomplete resection as in the presented case bears a favorable prognosis. Therefore, a function preserving less aggressive surgical approach is justified.