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Department of Radiology

Seth G.S. Medical College and K.E.M. Hospital, Mumbai , India

Case of the Month

< Case No. 41 : September 2023 >

Solitary plasmacytoma of the ilium

Contributed by: Chandrasekhar Khot

Other cases

Clinical Profile:

A 55-year-old woman presented with pain in the left hip, inability to walk, tingling and numbness in the left lower limb since two months following a trivial trauma at home.

Radiological findings:

The radiograph of the pelvis with both hips shows an ill-defined, expansile lytic lesion in the left iliac bone involving the left acetabular roof. It shows few areas of tiny calcifications. (Fig. 1)

Fig. 1 : Radiograph of the pelvis with both hips shows an ill-defined expansile, lytic lesion in the left iliac bone involving the left acetabular roof.

Ultrasonogram of the left iliac fossa and pelvis (Fig 2a) shows a well-defined heterogeneously iso to hypoechoic lesion with few calcific foci. THe lesion measures 10 x 9cm. It shows vascularity with a PSV of 20 cm/s. There is bone erosion in the underlying left iliac bone(Fig 2b).

Fig. 2 : Ultrasonogram of the left iliac fossa and pelvis shows a well-defined , heterogeneously iso to hypoechoic lesion with vascularity (2a). There is lytic bone erosion in the underlying left iliac bone (2b).

CECT of the abdomen and pelvis (Fig 3) shows a large, permeative lytic lesion involving the left iliac blade, acetabulum, left sacral ala . There is a large heterogeneously enhancing soft tissue measuring 11x8x12 cm . There are multiple areas of cortical breach in the involved bones. Spiculated periosteal reaction is seen in the lateral aspect of the left iliac blade.

Fig, 3 : Axial, coronal and sagittal sections of CECT Abdomen and pelvis (3a to 3c-plain,3d to 3f-contrast, shows an extensive permeative lytic lesion involving left iliac blade, acetabulum, left sacral ala with surrounding large heterogeneously enhancing soft tissue. There are multiple areas of cortical breach in the involved bones with spiculated periosteal reaction.

MRI Pelvis with both hips (Fig 4) shows a well defined lobulated heterogeneously STIR hyperintense (Fig 4a), T1 hypo to isointense (Fig 4b) and PD hyperintense (Fig 4c and 4d) soft tissue lesion centered around the medial aspect of the left iliac blade. It shows heterogeneous enhancement on post contrast sequences. Inferiorly. it extends into the acetabular roof of the left hip joint causing irregularity of acetabular articular surface. Posteriorly , it reaches upto gluteus maximus muscle. Medially, the lesion obliterates the left sacroiliac joint and involves the adjacent sacral ala. The iliac vessels are correspondingly displaced.

Fig, 4 :Axial and coronal sections of MRI Pelvis with both hips shows a well defined lobulated heterogeneously STIR hyperintense (Fig 4a), T1 hypo to isointense (Fig 4b) and PD hyperintense (Fig 4c and 4d) soft tissue lesion epicentered around the medial aspect of the left iliac blade. It shows heterogenous enhancement on post contrast sequences(4e).

Whole Body FDG PET shows metabolically active, lytic bone lesion involving left pelvic bone and sacrum. Metabolically active lung changes are seen, likely of infective etiology.

Fig, 5 : Whole Body FDG PET shows metabolically active lytic bone lesion involving left pelvic bone and sacrum. Metabolically active lung changes are seen, likely of infective etiology.

Radiologiclal dignosis:

Based on imaging features, the differentials considered were:

• Plasmacytoma

• Malignant fibrous histiocytosis

• Metastases

• Ewings sarcoma

Pathological Dagnosis:

Sonography guided biopsy of the soft tissue lesion around iliac bone was done. Histopathological examination(Fig 6) shows a malignant tumour with plasmacytoid morphology. There is marked proliferation of sheets of small round lymphocytes with little cytoplasm, variable numbers of plasmacytoid lymphocytes, and well-developed plasma cells. On immunohistochemistry, the tumour cells express CD138 and MUM1; are weakly positive for CD20 and AE1/AE3. These features are suggestive of Plasmacytoma.

Bone marrow biopsy: shows normocellular bone marrow with 2% plasma cells.

Final Diagnosis:

Solitary bone plasmacytoma

Treatment:

The patient is currently planned to be initiated on chemotherapy and radiotherapy.

Fig. 6 : Histopathological examination shows malignant tumour with plasmacytoid morphology.

Timeline :

Discussion:

Solitary plasmacytoma (SP) is characterized by a localized accumulation of neoplastic monoclonal plasma cells without evidence of a systemic plasma cell proliferative disorder (1). They account for 3-6% of all plasma cell neoplasia. There is minimal or no systemic bone marrow involvement in contradistinction to multiple myeloma (2).

Types of solitary plasmacytomas have been described (3).

Solitary bone plasmacytoma (approximately 70%)
Extramedullary plasmacytoma (approximately 30%)

Solitary bone plasmacytomas are localized to bone. They may involve any bone, but they have a predisposition for the red marrow-containing axial skeleton: spinal disease is observed in ~50% of cases. The thoracic vertebrae are most commonly involved, followed by lumbar, sacral, and cervical vertebrae. The rib, sternum, clavicle, or scapula are involved in 20% of cases.

The peak incidence is in 4th to 6th decades. The median age of presentation is 55 years, that is 10 years younger than patients with multiple myeloma. They show male predisposition with ~2:1 ratio.

Clinical presentation:

Symptoms are mainly related to the site of involvement. If vertebrae are involved, root or spinal cord compression syndrome may be seen.

The most common symptom of solitary bone plasmacytoma is pain at the local site due to bone destruction by the tumour. Pathologic fractures are seen, if long weight bearing bones are involved.

Diagnostic criteria:

For a diagnosis of SP, the International Myeloma Working Group (IMWG) requires all four of the following criteria (4) to be met :

• Biopsy-proven solitary lesion of bone or soft tissue with evidence of clonal plasma cells

• Normal bone marrow with no evidence of clonal plasma cells

• Normal skeletal survey and MRI (or CT) of the spine and pelvis, except for the primary solitary lesion

• Absence of end-organ damage, such as CRAB (hypercalcemia, renal failure, anemia, and osteolytic bone lesions), that can be attributed to a lympho-plasma cell proliferative disorder

Imaging features (5):

Plain radiograph

Solitary, expansile lytic lesion with thinning and destruction of the cortex, and bubbly/trabeculated appearance. Characteristically, there is no sclerotic reaction.

CT

Expansile lytic lesion with thinned out cortex and characteristic 'mini-brain' appearance has been described in solitary vertebral lesions.

MRI

A mini-brain appearance (6) has also been described on MRI. Curvilinear low signal intensity areas within the lesion give it an appearance of sulci in the brain. This appearance is so characteristic that it may obviate the need for a diagnostic biopsy.

Signal characteristics include:

T1: hypo- to isointense

T2: iso- to hyperintense to muscle

T1 C+ (Gd): variable enhancement

Differential diagnosis:

Differentials considered on imaging are: chronic osteomyelitis, osteolytic metastasis, osteoid osteoma, osteoblastoma, inclusion cyst, Brown tumour of hyperparathyroidism, aneurysmal bone cyst, benign giant cell tumour.

Management:

Excision of the tumour with adjuvant chemoradiotherapy is done. Local recurrence is less than 5% and dissemination is seen in 35-70% of patients. The disease may progress to multiple myeloma, with a bad prognosis (7).

References:

1. Wang Y, Zhu XL, Peeroo MW, Qian ZH, Shi D, Wei SM, Yu RS. Pelvic Solitary Plasmacytoma: Computed Tomography and Magnetic Resonance Imaging Findings with Histopathologic Correlation. Korean J Radiol. 2015 Jan-Feb;16(1):146-153. https://doi.org/10.3348/kjr.2015.16.1.146

2. Dimopoulos MA, Kiamouris C, Moulopoulos LA. Solitary plasmacytoma of bone and extramedullary plasmacytoma. Hematol Oncol Clin North Am. 1999 Dec;13(6):1249-57. doi: 10.1016/s0889-8588(05)70124-6. PMID: 10626148.

3. Galieni P, Cavo M, Avvisati G, Pulsoni A, Falbo R, Bonelli MA, Russo D, Petrucci MT, Bucalossi A, Tura S. Solitary plasmacytoma of bone and extramedullary plasmacytoma: two different entities? Ann Oncol. 1995 Sep;6(7):687-91. doi: 10.1093/oxfordjournals.annonc.a059285. PMID: 8664190.

4. [Guideline] Rajkumar SV. Updated Diagnostic Criteria and Staging System for Multiple Myeloma. Am Soc Clin Oncol Educ Book. 2016. 35:e418-23.

5. Ooi GC, Chim JC, Au WY, Khong PL. Radiologic manifestations of primary solitary extramedullary and multiple solitary plasmacytomas. AJR Am J Roentgenol. 2006 Mar;186(3):821-7. doi: 10.2214/AJR.04.1787. PMID: 16498114.

6. Major NM, Helms CA, Richardson WJ. The "mini brain": plasmacytoma in a vertebral body on MR imaging. AJR Am J Roentgenol. 2000 Jul;175(1):261-3. doi: 10.2214/ajr.175.1.1750261. PMID: 10882284.

7. Chak LY, Cox RS, Bostwick DG, Hoppe RT. Solitary plasmacytoma of bone: treatment, progression, and survival. J Clin Oncol. 1987 Nov;5(11):1811-5. doi: 10.1200/JCO.1987.5.11.1811. PMID: 3681369.

Acknowledgement :

We are grateful to the Department of Pathology at our institution for providing us with an image from the histological findings as also its description.

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