Imaging metastatic bone disease from carcinoma of the prostate

Abstract

Imaging bone metastases from prostate cancer presents several challenges. The lesions are usually sclerotic and appear late on the conventional X-ray. Bone scintigraphy is the mainstay of lesion detection, but is often not suitable for assessment of treatment response, particularly because of a 'flare' phenomenon after therapy. Magnetic resonance imaging is increasingly used in assessment, and newer techniques allow quantitation. In addition to (18)F-fluorodeoxyglucose ((18)FDG), newer PET isotopes are also showing promise in lesion detection and response assessment. This article reviews the available imaging modalities for evaluating prostatic bony metastases, and links them to the underlying pathological changes within bone lesions.

Figure 1

False-positive MDP bone scintigraphy. A male patient with prostate cancer and left sided sacral pain previously treated with IMRT, PSA <0.04. MDP bone scintigraphy (posterior view, A) showed a solitary focal area of uptake in the left side of the sacrum (arrow), interpreted as a bone metastasis. Symptom progression with bilateral sacral pain but PSA remaining <0.04 prompted an MRI, which showed bilateral oedema in the sacral ala (T1W coronal), (B) and a fracture through S2 (arrow) but no evidence of metastasis.

Figure 2

Flare response on MDP bone scintigraphy: metastatic disease in the inferior pubic rami (arrows, A) showed increased uptake 3 months after chemotherapy (B) that diminished at 6 months (C).

Figure 3

Schematic describing the relationship between patterns of tumour seeding in bone marrow and imaging findings.

Figure 4

A male patient with prostate cancer metastases to bone. T1W axial MRI pelvis (A) shows a metastasis within the right iliac bone (arrow). High signal within the lesion on the diffusion-weighted MRI of the pelvis (B) indicates that diffusion within the metastasis is less restricted than diffusion in the surrounding normal marrow. An apparent diffusion coefficient (ADC) map of pelvis (C) generated from the diffusion-weighted imaging data (B values 0, 50, 100, 250 500, and 750) provides a quantitative index of water diffusion within the tumour. The ADC map also shows heterogeneity of water diffusion within the tumour not shown by conventional T1W imaging.

Figure 5

Comparison of MRI and MDP bone scintigraphy: pelvic T1W MRI (A) and b750 DWI (B) of a patient with carcinoma of the prostate shows a new small metastasis (arrows) involving the left neck of femur. This small intramedullary lesion has not evoked enough osteoblastic reaction to become visible on bone scintigraphy (C).

Figure 6

Comparison of ¹⁸F-fluoride PET and MDP bone scintigraphy. (A) ¹⁸F-fluoride shows an increased number of metastatic deposits and better resolution than MDP bone scintigraphy (B) on the same patient.

Figure 7

Flow chart showing decision pathways for imaging metastatic bone disease in patients with carcinoma of the prostate. Experimental/non-validated techniques are in italics.