Radiological Findings-

A chest radiograph (Figure 1A) performed as a part of his routine yearly workup revealed a lytic lesion in the left glenoid. On further questioning, the patient reported mild stiffness in the left shoulder for the past year, without pain or restriction of movements.

Figure 1A

Frontal radiograph of the chest shows an ill defined mixed lytic-sclerotic lesion in the region of the left shoulder joint

A radiograph of the left shoulder (Figure 1B) showed a geographic lytic lesion with a sclerotic rim in the subarticular region of the glenohumeral joint, measuring approximately 3 x 4 cm. The lesion had a widezone of transition. There was cortical breach at the inferior glenoid margin with no periosteal reaction or calcifications. The glenohumeral joint space was preserved.

Figure 1B

Frontal radiograph of the left shoulder shows an ill-defined lytic lesion with areas of sclerosis in the subarticular region of the glenohumeral joint measuring approximately 3x4 cm with a narrow zone of transition (black arrow). A cortical breach is noted (arrowhead). There are no areas of calcification or surrounding sclerosis. The glenohumeral joint is normal (white arrow) . Fibrocalcific scars are seen in the left upper zone.

Figure 2. CT scan of the left shoulder in the axial plane shows the extension of the lytic lesion towards the base of the coracoid process.

Figure 3. CT scan of the left shoulder in the coronal plane shows a well-defined lytic lesion seen in the subarticular region of the glenohumeral joint measuring 1.9 x 2.9 x 4.9 cm (APxTRxCC). There are thin internal bony septations, cortical thinning and breach (black arrow). There are no areas of matrix calcification. The surrounding soft tissue is normal. The glenohumeral joint is normal. 

MRI revealed a lobulated T2 hyperintense lesion with internal hypointense septae with no significant post-contrast enhancement or diffusion restriction (Figures 4 to 9).

Figure 4,5. MRI of the left shoulder- axial and coronal planes of PDFS Sequence show a well defined expansile PDFS hyperintense lesion in the subarticular region of the gleno-humeral joint.

Figure 7. MRI- pre contrast T1 sequence shows T1 Hypointense lesion  

Figure 8.9  MRI- post contrast T1 sequence in axial and coronal plane shows no enhancement

Radiological diagnosis:

On imaging the differential diagnoses considered were in the following order-

1. A cartilage based tumour such as chondromyxoid fibroma

2. Plasmacytoma

3. Metastasis from an unknown primary

Pathological diagnosis:

A CT guided biopsy of the lesion was performed

Histopathology and immunohistochemistry confirmed the diagnosis of a plasma cell neoplasm. 

Management:

Discussion:

A plasmacytoma is a rare plasma cell dyscrasia resulting from autonomous irreversible proliferation of plasma cells involving bony or soft tissue and can occur anywhere in the body without evidence of systemic disease. It is an early plasma cell malignancy and is considered an intermediate phase between monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma. It is divided into two groups according to the International Myeloma Working Group.

1 Solitary Plasmacytoma which is subdivided into 

a. Solitary plasmacytoma  of bone which arises from the plasma cells of bone marrow

b. Extramedullary plasmacytoma (EMP) which arises from the plasma cells of mucosal lining.

2 Multiple Solitary Plasmacytomas (MSP)

Multiple solitary plasmacytoma is less prevalent than solitary plasmacytoma and has a poorer prognosis. It can progress to multiple myeloma if not evaluated and promptly managed. Solitary bone plasmocytoma can occur in any bone but has predisposition for the red marrow-containing axial skeleton. Most common sites include spine (50%), rib, sternum, clavicle, or scapula (20%). Plasmacytoma is prevalent in older individuals, African Americans, and males.

Its peak incidence is seen in the 4th-6th decade of life with male predominance of 2:1. 

Clinically, it can present as a painful swelling, pathological fracture, stiffness or restriction of movement. 

EMP can occur anywhere in the body with 80% to 90% in the head and neck region and aerodigestive tract, mainly in the oral cavity, tonsillar fossa, nasal cavity, and paranasal sinuses, which may present with headache, nasal discharge, dysphagia, sore throat, epistaxis, and nasal obstruction

Solitary plasmacytomas account for less than 5% of plasma cell neoplasms and typically present in the spine, pelvis, or ribs. Glenoid involvement is rare, with few reports in the literature [1]. The imaging findings of a solitary, well-circumscribed lytic lesion with a sclerotic rim, narrow zone of transition, and absence of periosteal reaction or soft tissue extension are typical features [2].

The presence of a sclerotic rim and well-defined margins in our case argues against metastasis and lymphoma, which tend to be more aggressive and poorly marginated [3][4]. 

The absence of matrix calcification or chondroid components helps exclude chondroblastoma [5] and the lack of expansile nature and fluid-fluid levels makes giant cell tumor less likely [6].

Osteomyelitis usually shows more aggressive features such as periosteal reaction or sequestra, which were absent here [7].

MRI findings, particularly the T2 hyperintense lesion with internal septations and minimal contrast enhancement, are consistent with solitary plasmacytoma and further supported by histopathological confirmation.

In patients with HIV, bone lesions may prompt suspicion for infection or lymphoma; however, solitary neoplasms such as plasmacytoma should remain on the differential diagnosis, especially when systemic parameters are stable [8].

Differential Diagnoses:

The imaging differential diagnoses considered in this patient for a well-defined lytic lesion in the glenoid include:

1. Metastasis 

2. Plasmacytoma

3. Chronic osteomyelitis 

4. Giant cell tumor (GCT) 

5. Lymphoma 

Conclusion:

This case underscores the importance of thorough evaluation of incidental radiographic findings, particularly in immunocompromised patients and not to be overcome by satisfaction of search. Solitary plasmacytoma, though rare in the glenoid, should be considered in the differential diagnosis of well-defined lytic lesions. Imaging plays a crucial role in narrowing the differential, guiding biopsy, and management

References:

1. Soutar R, Lucraft H, Jackson G, Reece A, Bird J, Low E, Samson D; Guidelines Working Group of the UK Myeloma Forum; British Committee for Standards in Haematology; British Society for Haematology. Guidelines on the diagnosis and management of solitary plasmacytoma of bone and solitary extramedullary plasmacytoma. Br J Haematol. 2004 Mar;124(6):717-26. doi: 10.1111/j.1365-2141.2004.04834.x. PMID: 15009059.

2. Yu, M. H., Hong, S. H., Choi, J.-Y., Myung, J. S., Kim, S. J., Choi, J.-A., & Kang, H. S. (2009). MR imaging features of extraspinal plasmacytoma of bone. In J Korean Soc Radiol, J Korean Soc Radiol (Vol. 61, pp. 257–262)

3. Li Q, Wang L, Pan S, Shu H, Ma Y, Lu Z, Fu X, Jiang B, Guo Q. Skeletal muscle metastases on magnetic resonance imaging: analysis of 31 cases. Contemp Oncol (Pozn). 2016;20(3):242-50. doi: 10.5114/wo.2016.61568. Epub 2016 Aug 4. PMID: 27647989; PMCID: PMC5013688.

4. Mulligan ME, McRae GA, Murphey MD. Imaging features of primary lymphoma of bone. AJR Am J Roentgenol. 1999 Dec;173(6):1691-7. doi: 10.2214/ajr.173.6.10584821. PMID: 10584821.

5. Murphey MD, Walker EA, Wilson AJ, Kransdorf MJ, Temple HT, Gannon FH. From the archives of the AFIP: imaging of primary chondrosarcoma: radiologic-pathologic correlation. Radiographics. 2003 Sep-Oct;23(5):1245-78. doi: 10.1148/rg.235035134. PMID: 12975513.

6. Restrepo, C. S., Lemos, D. F., Gordillo, H., Odero, R., Varghese, T., Tiemann, W., Rivas, F. F., Moncada, R., & Gimenez, C. R. (2004). Imaging findings in musculoskeletal complications of AIDS. Radiographics, 24(4), 1029–1049. https://doi.org/10.1148/rg.244035151

7. Pineda C, Vargas A, Rodríguez AV. Imaging of osteomyelitis: current concepts. Infect Dis Clin North Am. 2006 Dec;20(4):789-825. doi: 10.1016/j.idc.2006.09.009. PMID: 17118291.

8. Murphey MD, Nomikos GC, Flemming DJ, Gannon FH, Temple HT, Kransdorf MJ. From the archives of AFIP. Imaging of giant cell tumor and giant cell reparative granuloma of bone: radiologic-pathologic correlation. Radiographics. 2001 Sep-Oct;21(5):1283-309. doi: 10.1148/radiographics.21.5.g01se251283. PMID: 11553835.