[Osteoblastic metastasis]

Case 22. Presentation

An elderly man with known prostate cancer was referred to an outside institution to be assessed for metastatic disease by magnetic resonance imaging (Figs. 1 and 2). From the magnetic resonance images, does he have metastatic disease? What other condition(s) must you consider. What additional radiologic study would be helpful in determining the diagnosis.?

Case 22. Diagnosis

Sagittal T[Symbol Not Transcribed]-weighted (Fig. 1) and T[Symbol Not Transcribed]weighted (Fig. 2) spin-echo (SE) images of the dorsal spine demonstrate diffuse homogeneous low signal intensity (SI) of the T6 vertebral body. On the T[Symbol Not Transcribed]-weighted SE series, the vertebral body appears enlarged, suggesting Paget's disease. Osteoblastic metastatic disease should also be a consideration, given the clinical history and MRI characteristics of the lesion.

Correlation with plain radiographs (Figs. 3 and 4) is helpful in distinguishing between these 2 conditions. Diffuse osteosclerosis of the T6 vertebra is noted. The absence of cortical thickening, trabecular coarsening and enlargement of the vertebra preclude the diagnosis of Paget's disease. (The apparent enlargement of the T6 vertebra observed on magnetic resonance imaging was due to the contiguity between the diffusely low SI of the vertebral body and the adjacent intervertebral disc spaces.) The diagnosis of osteoblastic metastatic prostate cancer was subsequently confirmed.

The majority of bony metastases demonstrate low SI on T[Symbol Not Transcribed]-weighted and high SI on T[Symbol Not Transcribed]-weighted SE images. However, through correlation of magnetic resonance imaging, computed tomography, plain radiography and histopathological examination, it is now known that predominantly osteosclerotic metastases may exhibit low SI on both T[Symbol Not Transcribed]-weighted and T[Symbol Not Transcribed]-weighted SE series.(f.1) Similar investigations in patients with Paget's disease have shown that low SI areas on T[Symbol Not Transcribed]-weighted and T[Symbol Not Transcribed]-weighted SE images correspond to areas of osteosclerotic Paget's disease.(f.2) Lastly fibrous lesions, for example fibrous dysplasia, tend to exhibit low SI on both T[Symbol Not Transcribed]-weighted and T[Symbol Not Transcribed]-weighted SE sequences. This was not included in the differential diagnosis because the spine is an uncommon site of fibrous dysplasia.

References

(f.1.) Petren-Mallmin M. Clinical and experimental imaging of breast cancer metastasis in the spine. Acta Radiol 1994;391(Suppl):1-23.

(f.2.) Roberts MC, Kressel HY, Fallon MD, Zlatkin MB, Dalinka MK. Paget disease: MR imaging findings. Radiology 1989;173:341-5.