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Orbital plasmacytoma and myeloma


Key points

  • Definition: Plasma cell tumors may present as a solitary bone plasmacytoma (SBP), extramedullary plasmacytoma (EMP), or multiple myeloma (MM). While orbital involvement is rare and may not be associated with MM at presentation, it habitually heralds the unwelcome unleashing of this formidable foe (see Figure 49-3 , C ).

    FIGURE 49-3 ■, A, T1 axial show huge homogeneous, mass with “grapefruit-like” septations, destroying bone and displacing brain with intracranial mass effect and edema. Clearly this tumor should have been diagnosed and treated earlier. B, Axial T2 through orbits shows very complex heterogeneous abnormality filling right orbit and displacing and invading adjacent structures. C, Axial T2 shows huge heterogeneous complex mass extending into anterior cranial fossa with mass effect causing considerable cerebral edema. Complex heterogeneous pattern corresponds to calcific/ossific features.

  • Synonyms: Solitary bone plasmacytoma (SBP), solitary extramedullary plasmacytoma (SEP).

  • Classic clue: a 60-year-old man presents with painless proptosis, diplopia, blurred vision, and decreased visual acuity and is found to have an extraconal soft tissue mass in the upper outer orbital quadrant with exopthalmos, hypoglobus, and bone destruction.

  • Solitary osseous plasmacytoma of orbit is very rare. It may present as a solitary orbital tumor or as part of a generalized systemic disease (MM).

  • Bilateral orbital plasmacytomas are extremely rare, having been reported in a handful of cases.

  • EMPs of the orbit are extremely rare tumors, originating outside bone marrow. ,

  • Orbital plasmacytoma is frequently the first manifestation of MM, but MM is frequently not found at initial presentation of SBP or EMP.

Imaging

General imaging features

Multiple myeloma

  • MM, by definition, involves multiple locations with characteristic features that are well appreciated and have been deftly described for decades in the literature (see Figure 49-3 , A ).

  • MM is usually appreciated as systemic, disseminated disease.

Solitary bone plasmacytoma

  • SBPs arise in bone marrow causing characteristic bony destruction.

  • SBP has a homogeneous appearance of pure soft tissue components on T1 and T2 (see Figures 49-1 , A and B ).

    FIGURE 49-1 ■, A, T1 axial image shows homogeneous fusiform abnormality along lateral aspect of left orbital wall isointense to EOM but clearly hypointense to orbital fat, displacing adjacent structures and causing exopthalmos. Indistinct orbital cortex suggests bony involvement. B, Axial T2 confirms findings on T1 and shows homogeneous soft tissue mass isointense to EOMs and cerebral cortex. C, Axial DWI shows bright restricted diffusion corresponding to the lesion portrayed on T1 and T2 images above. D, Axial ADC map shows low signal “ADC black hole” corresponding to abnormality involving left orbit demonstrated to be bright on DWI ( C ).

  • Has markedly heterogeneous appearance of calcified/ossified portions of tumor (see Figure 49-3 , C ).

  • Computed tomography (CT) shows focal lytic lesions expanding bone with soft tissue components.

  • Can cause bone remodeling or erosion.

Extramedullary plasmacytoma

  • EMP arises outside bone marrow from mucosal cells characteristically sparing adjacent bone.

  • Homogeneous contrast enhancement of soft tissue masses in areas without bone formation.

  • Bony involvement is not a significant feature.

  • Very rare.

  • EMP portrays a propensity for bilateralism.

  • Falls into a disparate group of neoplasms regarding location, tumor progression, and survival rate compared with SBP and MM.

Computed Tomography Features

  • Features divide into three groups—MM, SBP, and EMP—as described in General Imaging Features above.

  • Slightly hyperdense smoothly circumscribed orbital mass causing hypoglobus and exopthalmos.

  • EAP may show no bony involvement.

  • MM and SBP arise in bone and do have bony involvement.

  • See Plain Film Features later.

Magnetic Resonance ImagingFeatures

  • T1 isointense to muscle and brain but hypointense to orbital fat. Figure 49-1 is isointense to cortex on T1 (see Figure 49-1 , A ).

  • T2 isointense to muscle and brain. , Figure 49-1 is isointense to cortex on T2 (see Figure 49-1 , B ). May be quite heterogeneous, depending on amount of calcification/bone formation (see Figure 49-3, B and C ).

  • T1 gadolinium (Gd) is variable. “Significant contrast enhancement with central heterogeneity” is often noted. This heterogeneity correlates with the amount of calcification and/or ossification seen on CT.

  • May show “grapefruit-like” septations (see Figure 49-3 , A ).

  • Short tau inversion recovery (STIR) is a fat suppression technique that often improves imaging of bony lesions.

Plain film features

  • May see well-defined, “punched-out” lytic lesions (see Figure 49-2 ).

    FIGURE 49-2 ■, Clear case of multiple “punched-out” lytic lesions depicted by lateral skull radiograph characteristic of MM. If present, this finding can clinch the diagnosis in an otherwise complex case.

  • Often see associated soft tissue masses.

  • As disease progresses, erosion, expansion, and destruction of bone cortex with thick peripheral ridging can cause characteristic “soap bubble” appearance.

Clinical issues

Presentation

  • Presenting problems include proptosis, diplopia, blurred vision, decreased visual acuity.

  • Rarely involves lacrimal sac and presents with epiphora. (Differential diagnosis: lacrimal sac lesion. See Chapter 43 : Squamous Cell Carcinoma of the Lacrimal Sac.)

  • EMP is 90% unilateral, 10% bilateral.

  • Usually unilateral. Bilateral orbital plasmacytomas are extremely rare, reported sporadically in a handful of cases.

  • Onset of symptoms may be quite gradual, spanning several months.

Epidemiology

  • Male-to-female ratio is 3:1.

  • Usual onset age is 50 to 70 years. Orbital plasmacytoma has been described in children.

Treatment

  • Treatment varies according to stage, so quality imaging is important for determining proper treatment.

  • Treatment includes combinations of surgery, radiation therapy, and chemotherapy.

Prognosis

  • The average survival rate for EMP is 8.3 years compared with 20 months for MM.

  • Finding the remote sites outside the orbit is important for prognosis.

Pathology

  • Composed of plasma cell-modified β lymphocytes, which produce large quantities of antibodies (immunoglobulins, usually IgG) in serum and urine.

  • Urine protein electrophoresis is positive for Bence Jones protein in two thirds of patients with MM.

  • The spectrum extends from benign, localized reactive lesions to low-grade monoclonal malignancy.

  • Plasma cell tumors are classified into SBP arising from bone, EMP arising from soft tissues, or MM.

  • EMPs primarily occur in head and neck region.

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