Applied Radiology

Prepared by Stephen Waite, MD ; Richard Batz, MD ; and Caren Jahre, MD of the Department of Radiology, Lenox Hill Hospital, New York, NY.

CASE SUMMARY

A 68-year-old woman with a medical history of multiple myeloma, hypertension, and hypothyroidism was admitted to the hospital for fever of unknown origin and generalized malaise. Her multiple myeloma was reportedly in remission and she had previously undergone chemotherapy.

Physical examination demonstrated a nonfocal neurologic examination. Laboratory findings were significant for thrombocytopenia, anemia, and hypercalcemia. A few days after admission, the patient acutely developed an expressive aphasia and incontinence, which prompted a computed tomography (CT) scan of the head (Figures 1 and 2).

DIAGNOSIS

Intracranial plasmacytoma

IMAGING FINDINGS

A head CT demonstrated a 2.4 * 3 cm hyperdense extra-axial left frontal mass with a rim of greater hyperdensity (Figure 1). There is a significant amount of surrounding edema and associated transfalcine herniation. There was bone destruction at the site of the lesion as well as multiple small uniform lytic lesions throughout the calvarium (Figure 2).

A subsequent MRI examination demonstrated the mass to be extra-axial, hypointense on T1-weighted images (Figure 3), and isointense on fluid-attenuated inversion recovery (FLAIR) (Figure 4) and T2-weighted images (not shown). There is a thin rim of hyperintensity on T1-weighted images and hypointensity on T2 weighted images. There was intense enhancement with an associated dural tail (Figure 5), as well as extensive vasogenic edema (Figure 4).

Subsequent surgical resection revealed an extra-axial mass consisting of immature plasma cells that extended into the brain, consistent with a plasmacytoma. The adjacent calvarium was invaded by tumor.

DISCUSSION

Multiple myeloma is the most common primary malignant bone tumor and accounts for approximately 27% of biopsied bone tumors. It is the result of malignant proliferation of plasma cells that infiltrate the bone marrow. In the classic form, the skeleton contains multiple permeative lesions that are filled by masses of neoplastic plasma cells. Areas of increased osteoclastic activity surround these focal collections of plasma cells. The radiographic hallmark is the sharply circumscribed osteolytic defect. These lesions are multiple, round, and purely lytic involving virtually any bone. A plasmacytoma is a localized form of plasma cell infiltration. ¹

Neurologic complications occur in up to 40% of patients with multiple myeloma. ² Often patients have neurologic symptoms from metabolic disturbances, such as hypercalcemia and hyperviscosity states. Often the mechanical effects of local tumor or displaced bone compress neural structures such as the spinal cord. ³ Other neurologic manifestations of myeloma include diffuse leptomeningeal disease. Intracranial involvement by multiple myeloma, however, is an uncommon finding. ⁴ It can manifest as a solitary tumor in the dura mater without invasion of the brain parenchyma, an intra-axial tumor without attachment to the dura mater or bone, or an invasive tumor that may grow from the dura mater into the brain. ^{3, 5-7} The most common sites of intracranial plasmacytoma are the body of the sphenoid bone, juxtasellar region, petrous apex, cerebral convexity, or falx region. ⁴

The typical clinical presentation of an intracranial plasmacytoma is that of an intracranial mass with focal neurological signs, seizures, or increased intracranial pressure, although there are no pathognomonic clinical features. ³

The presence of abnormal serum or cerebrospinal fluid (CSF) immunoglobulins in electrophoresis studies has been reported in intracranial plasmacytomas. Monitoring the level of CSF paraprotein is thought to serve as a marker for tumor recurrence and a decrease in the level is to be expected postoperatively. ⁶

Plasmacytomas are seen on CT examination as isodense to hyperdense lesions that homogeneously enhance after administration of a contrast agent. On MRI, these lesions are hypointense to isointense on T1-weighted images and usually hyperintense on T2-weighted images with dense uniform enhancement after gadolinium administration. ^4,8 Focal calcification or bone erosion without sclerosis may be seen. Spontaneous hemorrhage into an intracranial plasmacytoma has also been described. ⁷

The radiologic signs are not specific and may mimic a meningioma, lymphoma, metastasis, and sarcoma ⁷ ; however, the presence of osteolytic lesions is thought to suggest a plasmacytoma, as meningiomas more often produce a hyperostotic reaction. Plasmacytomas are also more often hyperintense to muscle on T2-weighted images possibly because of intracellular immunoglobins. ⁷ Meningiomas, on the other hand, are usually isointense on all pulse sequences.

This case of intracranial plasmacytoma manifested as a hyperdense lesion with intense enhancement, both classic findings. It is, however, atypical in that it was isointense on FLAIR and T2-weighted images. It was associated with a lytic lesion, suggesting the possibility of a plasmacytoma versus the much more common meningioma, which is usually associated with hyperostosis.

It is important to note that this patient's intracranial plasmacytoma developed as part of the diffuse plasmacytic bony involvement of multiple myeloma. This is important because patients with a solitary intracranial plasmacytoma have a more favorable clinical course. The finding of an intracranial plasmacytoma therefore necessitates looking for systemic disease; and if isolated, follow-up is important, as these lesions often terminate in multiple myeloma.

If the preoperative diagnosis is a solitary intracranial plasmacytoma, the current treatment of choice is surgical removal and/or radiation therapy. These tumors are, in general, radiosensitive and regress in almost every case after local irradiation. Chemotherapy is suggested for systemic disease. ⁵

CONCLUSION

Although rare, an intracranial plasmacytoma should be in the differential diagnosis of an extra-axial mass, especially in patients with multiple myeloma or with an associated calvarial lytic lesion.