Primary Lymphoma of Bone

= RETICULUM CELL SARCOMA = OSTEOLYMPHOMA

= singular bone lesion without evidence of distal nodal /disseminated disease for at least 6 months after diagnosis (= stage E in Ann Arbor classification)

N.B.: presence of locoregional lymphadenopathy is not a criterion of exclusion

Prevalence:<5% of all primary bone tumors; <1% of all NHL; 5% of extranodal lymphomas; 2–6% of all primary malignant bone tumors in children

Histo:

1. NHL (94%): mostly diffuse large B-cell (80%) / T-cell category; sheets of reticulum cells, larger than those in Ewing sarcoma (DDx: myeloma, inflammation, granulocytic osteosarcoma, eosinophilic granuloma)
2. Hodgkin disease in 6%

Median age: 36–52 (range, 1.5–86) years; bimodal distribution with peaks in 2^nd–3^rd and 5^th–7^th decades; 50% <40 years; 35% <30 years; M÷F = 6÷1

• intermittent chronic dull pain; local swelling, palpable mass
• systemic symptoms such as weight loss and fever
• striking contrast between lesion size + patient's well-being

Location: lower femur (25%), upper tibia (40% about knee), humerus, pelvis, head & neck, vertebra (25%), scapula, ribs

Site: meta- / diaphysis

Radiography:

• lytic process at end of a long bone with aggressive periosteal reaction (almost pathognomonic)
• lytic-destructive pattern (70%):
  • “permeative” pattern = numerous small elongated rarefactions parallel to long bone axis
  • “moth-eaten” pattern = many medium to large areas of radiolucency in poorly marginated area of bone
  • lamellated / layered “onion-peel” / broken periosteal reaction (60%):
    • disrupted periosteal bone (poorer prognosis)
    • sunburst periosteal response (rare and less than in Ewing sarcoma)
• blastic-sclerotic pattern (rare):
  • mixed lytic lesion with sclerotic areas
  • may develop after therapy
• near absence of detectable abnormalities on plain X-ray

CT:

• cortical destruction (late)
• sequestrum within lytic lesion

MR:

• bone marrow replacement:
  • areas of low signal intensity within marrow on T1WI
  • high SI on T2WI for tumor + peritumoral edema + reactive marrow changes
  • areas of enhancement within lesion
• soft-tissue involvement ← spread of tumor cells from marrow through small vascular channels through cortex into surrounding soft tissue:
  • soft-tissue mass without calcification (70%)
    N.B.: relatively minimal cortical destruction with extensive soft-tissue + marrow involvement
  • synovitis of knee joint common
• cortical erosion (earliest detection by MR)

Cx: pathologic fracture (25% = most common among malignant bone tumors)

Rx: combination of radiation therapy + chemotherapy

Prognosis: 83% 5-year survival

DDx:

1. Osteosarcoma (less medullary extension, younger patient)
2. Ewing tumor (systemic symptoms, debility, younger patient)
3. Metastatic malignancy / secondary lymphoma (multiple bones involved, more destructive, recognized by whole-body surveillance)