What is the differential diagnosis for lytic lesions in the cervical spine identified on a computed tomography (CT) scan?

Differential Diagnosis for Lytic Lesions in the Cervical Spine on CT

The differential diagnosis for lytic lesions in the cervical spine includes metastatic disease, multiple myeloma/plasmacytoma, infection (osteomyelitis/discitis), primary bone tumors (giant cell tumor, osteoblastoma, aneurysmal bone cyst), lymphoproliferative disorders (lymphoma, Castleman's disease), and rare entities such as fibrous dysplasia, epithelioid hemangioendothelioma, and unicameral bone cysts.

Primary Diagnostic Considerations

Metastatic Disease and Multiple Myeloma

• Metastatic disease is the most common cause of multiple lytic lesions in the spine, particularly in adults over 40 years old, with primary sources including lung, breast, kidney, thyroid, and prostate cancers 1.
• Multiple myeloma and solitary plasmacytoma characteristically present with lytic bone lesions that preferentially replace trabecular bone while cortical bone is partly conserved or even sclerotic 2.
• In two-thirds of plasmacytoma cases, the radiographic appearance shows a mixed, predominantly lytic pattern; less commonly, a multicystic appearance is seen 2.
• CT is the gold standard for identifying cervical spine fractures and lytic bone lesions with >98% sensitivity, detecting small (<5 mm) lytic lesions with high-resolution imaging of cortical and trabecular bone 2, 3.

Infectious Processes

• Osteomyelitis and discitis must be considered when lytic lesions are accompanied by neck pain, fever, or elevated inflammatory markers 4.
• Percutaneous aspiration biopsy is useful for distinguishing between metastatic and inflammatory processes, and can identify the causative organism when blood cultures are negative 4.
• Infectious lesions typically show associated soft-tissue changes and may involve adjacent disc spaces, which helps differentiate them from neoplastic processes 4.

Primary Bone Tumors

• Giant cell tumor, osteoblastoma, and aneurysmal bone cyst are the most common primary bone tumors causing lytic lesions in the cervical spine 5.
• Unicameral bone cysts, though rare in the cervical spine, can involve all three columns and present with pathological fractures 5.
• These lesions typically show cystic areas with sclerotic margins on CT and require histological confirmation 5.

Rare Entities

• Fibrous dysplasia rarely affects the cervical spine and may present with multiple lytic lesions mimicking metastatic disease 6.
• Epithelioid hemangioendothelioma should be considered when lytic lesions are clustered in the same anatomic region and may present with visceral involvement in lungs, liver, and kidneys 7.
• Castleman's disease, a rare lymphoproliferative disorder, can present as a destructive lytic lesion with spinal canal extension causing cord compression 8.

Algorithmic Approach to Diagnosis

Initial CT Evaluation

• CT without contrast is the first-line imaging modality for characterizing lytic lesions, providing superior detail of bone destruction, cortical integrity, and fracture risk 2, 3.
• Assess the pattern of bone destruction: purely lytic, mixed lytic-sclerotic, or geographic versus permeative 2.
• Evaluate for pathological fractures, spinal instability, and involvement of all three columns (anterior body, pedicles/lateral masses, posterior elements) 5.

MRI for Soft-Tissue Characterization

• MRI without and with IV contrast should follow CT when evaluating lytic lesions to assess soft-tissue extension, spinal cord compression, and marrow involvement 2, 1.
• MRI is superior to CT for detecting epidural disease, spinal cord compression, and neural foramina involvement—critical complications requiring urgent intervention 1.
• MRI detects very early marrow changes before cortical bone destruction occurs and provides definitive characterization of lesion extent 1.
• Solitary plasmacytoma appears as infiltration with low T1 and high T2 signal intensity on MRI 2.

Advanced Imaging Considerations

• 18F-FDG PET/CT is superior to bone scintigraphy for detecting lytic metastases (sensitivity 89.7%, specificity 96.8%) and offers simultaneous assessment of skeletal and extraskeletal disease 2, 1.
• PET/CT may show additional lesions not visible on CT or MRI in 33-55% of patients with presumed solitary lesions 2.
• Avoid MDP bone scan as primary imaging for lytic lesions due to poor sensitivity (62-100%) and low specificity (48%), particularly for purely osteolytic lesions 1.

Tissue Diagnosis

• Percutaneous aspiration biopsy or open biopsy is essential for definitive diagnosis when imaging findings are indeterminate or when distinguishing between metastatic, infectious, and primary bone lesions 4.
• Biopsy should be performed before initiating treatment to guide appropriate therapy and avoid misdiagnosis 4.

Critical Pitfalls to Avoid

• Never rely on CT alone when neurological symptoms are present—MRI is mandatory to evaluate for spinal cord compression and epidural extension 2, 1.
• Plain radiographs require 50-70% bone destruction before detecting osteolytic changes, so negative radiographs do not exclude significant pathology 1.
• Do not assume multiple lytic lesions automatically represent metastatic disease—rare entities like fibrous dysplasia, epithelioid hemangioendothelioma, and Castleman's disease can mimic metastases 6, 7, 8.
• Avoid using bone scan to monitor treatment response, as the "flare phenomenon" from healing osteoblastic activity can misleadingly suggest disease progression 1.
• In patients with solitary lytic lesions, whole-body imaging (PET/CT or whole-body MRI) is mandatory to exclude additional lesions before diagnosing solitary plasmacytoma or primary bone tumor 2.