Specific Imaging Findings

Chordoma is typically an exophytic mass centered in or around the clivus, characteristically at the midline. It is usually hypodense on CT, iso- to hypointense on T1WI, while predominantly and distinctively of high T2 signal. Chordomas often show septations and lobulations, giving a typical “honeycomb” heterogeneous appearance, with possible round areas of high T1 and low T2 signal. In rare cases they may be predominantly T2 hypointense. Areas of necrosis, hemorrhage, and sequestered bone fragments can cause signal heterogeneity. Chordomas show high diffusion with bright appearance on ADC maps. Post-contrast enhancement is usually heterogeneous and mild, and may be completely absent. CT shows to a better advantage the lytic nature of the lesion, with possible but rare areas of calcification and bone sequestra. Around 15% of these tumors originate off the midline.

Pertinent Clinical Information

The growth of chordomas is usually slow, which accounts for their insidious clinical presentation, often with headache, and/or cranial nerve deficits, most commonly abducens nerve palsy. Both CT and MRI are usually necessary for complete evaluation due to the involvement of soft tissue and bony structures at the skull base.

Differential Diagnosis

Chondrosarcoma (53)

1. • may be indistinguishable

2. • characteristically centered off midline, originating from the petro-clival junction

3. • chondroid matrix calcification (linear, globular, arc-like) is diagnostic, when present

Meningioma (47)

1. • absence of bone destruction

2. • isointense to low T2 signal, low ADC values

3. • intense and homogeneous contrast enhancement

Plasmocytoma/Metastasis

1. • typically pure lytic bone lesions, prominent exophytic component is rare

2. • usually darker T2 signal and lower ADC values

3. • usually more homogeneous pre- and post-contrast appearance