Key-words:
Mini brain - plasmacytoma - skull - vault
Introduction
Plasma cell neoplasms can be classified as multiple myeloma, solitary plasmacytomas
of bone, and extramedullary plasmacytomas.[[1]] Plasmacytomas can occur in soft-tissue lesions in soft tissue or bone.[[1]] They are most commonly found in the axial skeleton (thoracic and lumbar spine).[[1]] Skull vault plasmacytomas are rare lesions comprising 0.7% of all plasmacytomas.[[2]],[[3]] They can mimic meningiomas, osteogenic sarcomas, or metastatic carcinomas on radiologic
imaging.
Case Report
A 63-year-old-female presented to us with a swelling over the vertex of the skull
for the past 1 year which was insidious in onset, painless, of the size of a lemon
when it was first noticed and gradually progressed to achieve the present size of
about a cricket ball. The swelling was nontender on palpation and the overlying skin
was normal. On examination, she was conscious oriented and had no neurological deficits.
The progressively increasing scalp swelling made her seek medical attention. Noncontrast
computed tomography (CT) head done showed a large extra-axial swelling of size 10.3
cm × 8 cm × 7 cm over midline (left > right) frontoparietal parasagittal region causing
compression of underlying brain and erosion of skull [[Figure 1]]. Magnetic resonance imaging (MRI) brain [[Figure 2]] revealed a large heterogeneously enhancing lesion over midline (left > right) frontoparietal
parasagittal region. On magnetic resonance venogram [[Figure 3]], the middle part of the superior sagittal sinus was not visualized. Rest of the
veins was normal. A provisional diagnosis of parasagittal meningioma was made. On
digital subtraction angiography, tumor was fed by feeders from a bilateral superficial
temporal artery, middle meningeal artery, and occipital artery. During embolization,
dangerous anastomosis between anterior trunk of the middle meningeal artery and ophthalmic
was carefully ruled out before all feeders were superselectively embolized using polyvinyl
alcohol particles to achieve tumor devascularization. After embolization, the patient
was planned for surgery after 5 days. The patient's head was fixed in three pins and
positioned in a semi-sitting position. There was a large, gray white, soft-to-firm,
moderately vascular, extradural tumor destroying the calvarium. No dural or sinus
invasion was seen. The intraoperative impression was that of a tumor of bony origin.
Histopathology [[Figure 4]] revealed a tumor with sheets of plasmacytoid cells with large areas of necrosis
and microabscesses. The cells were round to oval with moderate amounts of cytoplasm
and eccentric nuclei. On immunohistochemistry, most cells were positive for CD138
and lambda light chain suggestive of a plasmacytoma. Serum light chain assay showed
grossly elevated lambda light chain levels. On serum electrophoresis, M spike was
not seen. Serum calcium levels and renal function were normal. Positron emission tomography
(PET) scan revealed uptake in C3, C4, and C5 vertebra and left iliac bone establishing
a final diagnosis of light chain myeloma. The patient was then referred to hematology-oncology
department for bone marrow evaluation and adjuvant chemotherapy.
Figure 1: (a) Noncontrast computed tomography head showing large hyperdense extra-axial lesion
over midline frontoparietal region. (b) Noncontrast computed tomography head (bone
window) showing erosion of the skull
Figure 2: (a) Magnetic resonance imaging showing an isointense tumor on T1-weighted sequence.
(b) Magnetic resonance imaging axial view showing a hyperintense tumor on T2-weighted
sequence. (c) Contrast-enhanced magnetic resonance imaging (coronal) showing heterogeneously
enhancing tumor (with appearance suggestive of sulci and gyri: mini-brain appearance;
see inset for illustration). (d) Contrast-enhanced magnetic resonance imaging (sagittal)
showing heterogeneously enhancing tumor (with appearance suggestive of sulci and gyri:
mini-brain appearance; see inset for illustration)
Figure 3: On magnetic resonance venogram, middle part of superior sagittal sinus was not visualized
Figure 4: (a) Low-power microscopy (H and E, x20) showing a cellular tumor lying in sheets.
Tumor is seen breaching the bone (arrow). (b) High-power microscopy (H and E, x40)
showing plasmacytoid cells with atypical and binucleate forms. (c) Immunohistochemistry
showing diffuse positivity for lambda light chain and absence of kappa chain (light
chain restriction)
Discussion
Myeloma is a hematological malignancy that originates from plasma cells of bone marrow.[[1]],[[2]] Plasma cell neoplasms can be classified into multiple myeloma, solitary plasmacytomas
of bone, and extramedullary plasmacytomas.[[1]],[[2]] While multiple myeloma is a systemic disease, solitary plasmacytoma and extramedullary
plasmacytomas are focal forms of plasma cell neoplasms. Plasmacytomas occur as mass
lesions in soft tissue or bone. Skull vault plasmacytomas are very rare, comprising
0.7% of all plasmacytomas, most common locations being thoracic and lumbar spine.[[2]],[[3]] As per our information, this is the first case report of a plasmacytoma in a parasagittal
location which closely mimicked the appearance of a parasagittal meningioma.
In such cases, a differential diagnosis of meningioma, osteosarcoma, metastatic carcinoma,
and plasmacytoma must be considered. We considered meningioma as the most likely possibility
because of its common occurrence in the parasagittal location. For meningioma, it
must be remembered that they rarely cause osteolysis albeit for intraosseous forms.[[4]] Osteosarcomas occur mostly in long bones and rarely involve the skull when they
cause the destruction of outer table and present as extracranial masses.[[2]],[[4]] Osteolytic metastatic carcinoma is usually multiple and has punched out margins.[[4]]
Plasmacytomas may be identified as osteolytic lesions on X-ray.[[2]],[[4]],[[5]] On a CT scan, they are seen as osteolytic lesions without sclerotic rim and homogeneous
contrast enhancement. They show variable intensity on T1-weighted images but enhance
strongly on administration of gadolinium.[[4]],[[5]] The sharp borders of the lesion, lack of sclerosis, and minimal periosteal reaction
are strongly suggestive of a plasmacytoma. In our case, lesion was hyperintense, osteolytic
without sclerosis on the CT scan. It was hyperintense on T1 and was heterogeneously
contrast enhancing on MRI. On retrospective review, lesion was seen to have “mini-brain
appearance.” “Mini-brain appearance” was first described by Major et al. in their
series of spinal plasmacytomas.[[1]] As in our case, “mini-brain appearance” can be retrospectively seen in cases of
calvarial plasmacytomas reported in the literature [[Table 1]]. We feel that finding this characteristic appearance can aid in forming a radiological
diagnosis of a calvarial plasmacytomas even in locations where this lesion is extremely
rare.
Table 1: Reported cases of skull vault plasmacytoma with "mini-brain appearance"
For embolization of tumors fed by the middle meningeal artery, overt and covert “dangerous
anastomosis between anterior trunk of the middle meningeal artery and ophthalmic artery”
must be ruled out during angiography and superselective distal embolization of tumor
feeders must be done to avoid catastrophic complications.
Chemotherapy is the treatment of choice for multiple myeloma.[[2]] Skull plasmacytomas are treated by excision followed by radiotherapy.[[6]],[[7]] After a diagnosis of skull plasmacytoma, patients must be evaluated for myeloma
using a battery of tests such as serum light chain assay, serum electrophoresis, urine
for Bence–Jones protein, PET scan, and bone marrow examination.[[9]] The monoclonal nature of tumor cells must also be confirmed to rule out the possibility
of plasma cell granuloma. The prognosis of solitary plasmacytomas and extramedullary
plasmacytomas is better as compared to that of multiple myeloma.[[7]],[[8]] These patients must be followed up closely to detect progression to multiple myeloma.
Conclusion
Skull vault plasmacytomas are rare lesions. Their appearance can often mimic other
skull vault lesions such as meningioma, osteosarcoma, and metastatic carcinoma. Findings
of “mini-brain appearance” can help in the formation of diagnosis in such cases.
Declaration of patient consent
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understand that their names and initials will not be published and due efforts will
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