Parietal swelling in an old female: A diagnostic conundrum

Q1. What is your interpretation?

1. Plasma cell lesion

2. Hematopoietic cells

3. Infective etiology

4. Benign neoplasm

Answer 1: Option a – Plasma cell lesion

Explanation

The aspirate showed moderate cellularity with cohesive fragments of predominantly round cells having inconspicuous nucleoli and fine granular chromatin. Few interspersed cells with eccentric nuclei and pale cytoplasm were noted. Magnetic resonance imaging (MRI) of brain showed an extra-axial homogenously enhancing solid lesion measuring 3.8 × 3.6 cm in the left parietal region involving skull vault and scalp, isointense on T1W [Figure 2a], and heterogeneously hyperintense on T1W with gadolinium [Figure 2b]. There was mild compression of the adjacent brain parenchyma. Rest of the cerebral parenchyma appeared normal with maintained gray-white matter differentiation. Both the cerebellar hemispheres and brainstem showed normal morphology.

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Figure 2:

(a) T1W MRI of the brain showing a well-defined, extra-axial, isointense lesion in the left parietal region. (b) The same lesion is heterogeneously hyperintense on T1W gadolinium-enhanced MRI.

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Q2. What is the most likely cytological diagnosis?

1. Meningioma

2. Solitary plasmacytoma of skull

3. Multiple myeloma with associated bony plasmacytoma

4. Metastatic tumor

Answer 2: Option b – Solitary plasmacytoma of skull

Explanation

Multiple FNA was done from the scalp mass. Smears revealed moderate cellularity comprising clusters of round to oval cells with fine chromatin and inconspicuous nucleoli and also seen were interspersed plasma cells with eccentric nuclei and moderate amount of pale bluish cytoplasm. Binucleate cells with few reactive forms were noted [Figure 1b]. Occasionally, plasmablasts-like cells were seen with high N:C ratio, large round to ovoid, central to eccentric nucleus, and evident nucleoli. The patient was operated for the swelling and intraoperative squash smears were prepared. Smears showed moderate cellularity with sheets and singly dispersed cells of similar morphology with many bi/multinucleate forms [Figure 1c and d]. No evidence of mitosis or necrosis was seen.

Cytomorphological features and radiological findings were suggestive of solitary plasmacytoma of skull. However, a possibility of multiple myeloma (MM) could not be excluded because biochemical investigations were within normal limits, but other ancillary investigations such as complete skeletal survey, serum/urine electrophoresis, and bone marrow examination were not performed.

The diagnosis of meningioma is eliminated as the classical features such as intranuclear cytoplasmic inclusions, whorling pattern, and psammomatous calcification were not found. Sometimes, in rare cases, unusual cytomorphologic features including plasmacytoid appearance may be seen.^[1]

Of the metastatic tumors, plasmacytoma may be misdiagnosed as malignant melanoma because of the eccentric nuclei, but it is a less likely diagnosis in our case as there is no pseudo-inclusion, melanin pigment, and frequent mitoses. Metastasis from neuroendocrine tumors (NETs) could still be kept as a differential, however, NET cells are rounder with salt and pepper chromatin, and frequent mitotic figures.

Q3. What is the definite diagnosis?

1. Solitary plasmacytoma of bone (SBP)

2. Multiple myeloma with associated plasmacytoma

3. Meningioma with plasmacytoid pattern

4. Metastasis

Answer 3: Option b – Multiple myeloma with associated plasmacytoma

Explanation

Surgery for excision of the parietal bony mass lesion was performed. There was grayish-colored tumor tissue adherent to dura which was scraped off. Both the soft tumor tissue and involved bony tissue were sent for histopathological examination. Routine processing was done and hematoxylin and eosin staining was performed. Sections showed sheets of plasmacytoid cells infiltrating the bone [Figure 3a]. Occasional binucleated plasma cells were also noted. The cells strongly expressed CD138 and kappa light chain restriction [Figures 3b-d] and were negative for CD56 and cytokeratin, consistent with the diagnosis of plasmacytoma. The absence of CD56 rules out the possibility of metastatic NET.

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Figure 3:

(a) Tissue sections from parietal mass showing sheets of plasma cells involving the bone (H&E, ×100). (b) Plasma cells showing diffuse membranous positivity for CD 138 (×100). (c) Nuclei of plasma cells showing diffuse kappa positivity (×100). (d) Nuclei of plasma cells negative for lambda (×100).

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A workup for MM was advised including all the necessary investigations. Contrast-enhanced computed tomography (CECT) chest revealed multiple erosive lesions in dorsolumbar vertebrae and bony thoracic cage. Serum protein electrophoresis showed monoclonal gammopathy with a serum M protein concentration of 3.50 g/dl [Figure 4]. Serum calcium was 10.1 mg/dl, serum creatinine was 0.6 mg/dl, serum albumin was 3.5 g/dl, and beta-2 microglobulin was 4.2 mg/ml. These findings were consistent with multiple myeloma ISS Stage II. Bone marrow aspiration and biopsy were also performed simultaneously which showed 45% plasma cells with strong CD 38 positivity and kappa restriction. In view of above histomorphological and immunohistochemical (IHC) features, in conjunction with serum electrophoretic and bone marrow findings, a final diagnosis of multiple myeloma with associated plasmacytoma of bone was rendered.

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Figure 4:

(a) Serum protein electrophoresis: Densitometric tracing showing M-spike. (b) Serum protein electrophoresis: Gel picture showing M-band.

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ADDITIONAL QUIZ QUESTIONS

SUMMARY

Solitary plasmacytoma can be the initial presentation of multiple myeloma so a thorough clinical, hematological, and biochemical workup along with skeletal survey is necessary in all cases. Correct diagnosis in such cases helps in planning proper treatment and results in prolonged overall and progression-free survival.