A 31‐Year‐Old Woman with a Destructive Clival Mass

Clinical History

A 31‐year‐old woman presented with worsening neck pain for 2 weeks. She was treated for muscle spasms at an urgent care clinic with muscle relaxants and narcotic pain medication, but had no relief of symptoms. On physical examination, she had focal tenderness in the midline at the base of the occiput and resistance to any motion of the neck. Routine laboratory examination was unremarkable. There was no associated history of trauma. Computed tomography (CT) scan showed a large, expansile and destructive mass in the right clivus extending into the right petrous bone with associated right medulla effacement (Figure 1A). Follow‐up with magnetic resonance imaging (MRI) again showed a 5.0 × 3.0 × 3.0‐cm expansile, destructive mass in the right clivus and along the right anterolateral margin of the foramen magnum/base of the skull (Figure 1B).

Figure 1.

 

Microscopic Pathology

Microscopic examination showed large areas of calcification separated by fibrous material (Figure 1C). On higher power, the calcification appears chunky and plate‐like (Figure 1D). The fibrous tissue is composed of spindle cells without mitoses, necrosis or pleomorphism. Some areas have an epithelioid appearance (Figure 1E). Scattered throughout the lesion are multinucleated giant cells (Figure 1F). S‐100, EMA, GFAP, Desmin and pan keratin were negative. Reactive stromal myofibroblasts were seen with SMA, and CD163 highlighted histiocytes. What is the diagnosis?

Diagnosis

Calcifying pseudoneoplasm of the neural axis (CAPNON).

Discussion

CAPNON was first described by Rhodes and Davis in 1978 5, and since then has been found anywhere along the neural axis from L2 to the frontal lobe 1, 2, 4, 6. The age range is highly variable as well, ranging from 6 to 83 years 1, 3. To date, only 32 cases have been reported in the English literature 1.

Calcifying pseudoneoplasm of the neural axis has multiple histopathologic features that may be present, including chondromyxoid matrix, palisading spindled to epithelioid cells, calcifications, fibrous stroma and a foreign body giant cell reaction 1. Although the components are similar from case to case, the distribution may vary 2, and some features may not be seen at all 1. In our case, the calcification manifested as large areas of chunky and plate‐like material. Spindle cells predominated as the cellular component, although occasional areas showed an epithelioid appearance. Multinucleated giant cells were seen scattered throughout the lesion, although they did not have a granulomatous appearance as described in other literature 2. The chondroid matrix, psammoma bodies and osseous metaplasia, which have been described in other cases 1, 2, were not seen in our case.

The differential diagnosis of CAPNON can be fairly broad, depending on the features present. The calcifications seen in this case are very similar to that of phosphaturic mesenchymal tumor and tumoral calcinosis; however, the patient did not have a clinical history of hypophosphatemia or hyperphosphatemia. Given the presence of multinucleated giant cells, a granulomatous reaction may be considered. However, there was no necrosis or rim of lymphocytes, and the multinucleated giant cells were scattered rather than localized. The epithelioid component had a whorled pattern similar to a meningioma, but did not stain for EMA or S‐100. Chondroid or osteoid is often seen in CAPNON, and if present, a chondrosarcoma or osteosarcoma may be considered. CAPNON is a diagnosis of exclusion and should not be made until other possibilities have been ruled out.

CAPNON is believed to be a reactive process 1, 3 and fibroblasts have been proposed to be the precursors of this lesion 3. It is important to note that the lesion is benign and treated with resection without chemotherapy or radiation 2. There have been fatalities reported caused by CAPNON, but from complication related to the anatomic location, and not because of the progression of disease 2.