Teaching Case

An 88-year-old man diagnosed with non-metastatic prostate cancer 5 years before developed pain in his right hip during weight-bearing activities. No other complaints. PSA = 183µg/l. He previously had a left-sided total hip replacement surgery due to osteoarthritis.

The working diagnoses were 1) osteoarthritis of the right hip and 2) bone metastases from prostate cancer. The following diagnostic imaging procedures were done within 5 weeks according to our protocol, and the treatment was unchanged in that period.

Radiography of the pelvis showed right-sided osteoarthritis and left-sided total hip replacement. No bone lesions. (fig. 1)

Whole-body bone scintigraphy performed with 99m-Tc HDP showed a few bone metastases. (fig. 2)

NaF-PET/CT scan showed multiple bone metastases. (fig. 3)

MRI of abdomen and pelvis (diffusion-weighted, T1-weighted with and without i.v. gadolineum and T2-weighted images) showed multiple bone metastases and extraosseous metastases located to lymph nodes (fig. 4, 5, 6, 7)

Conclusion: The patient was diagnosed with osteoarthritis in the right hip and prostate cancer bone metastases and lymph node metastases.

Prostate cancer is the second most diagnosed cancer in the developed world, and the skeleton is the primary site of metastases [1, 2]. Imaging for metastases should be undertaken when PSA is ≥ 10µg/l and/or Gleason score is ≥ 7. These criteria may vary from place to place. The question is how to diagnose bone metastases?

Conventional radiography has been used for many years, but as known from literature and as shown in this case, radiography is not very sensitive in regard to bone metastases [3].

For the last 40 years bone scintigraphy has played a major role in the diagnosis of bone metastases.
Bone scintigraphy is performed with technetium-labelled diphosphonate and a gamma camera. The degree of tracer uptake reflects the osteoblastic reaction to the presence of tumour cells [1, 4]. It is a very sensitive method, however, very unspecific, as illustrated in this case, where the bone scintigraphy showed tracer uptake in the right hip due to osteoarthritis, which gives rise to increased bone turnover. There were several hot spots indicative of metastases.

18F-NaF-PET/CT is increasingly used for bone metastases. 18F-NaF is a bone seeking tracer for skeletal imaging and an indicator of bone turnover comparable to diphosphonate used for bone scintigraphy. However, 18F-NaF has more favourable kinetic characteristics, which results in a better bone-to-background ratio, and the PET camera offers a higher spatial resolution. The integrated CT scanner makes anatomic mapping possible [1, 5]. In this case several more hot spots appeared on 18F-NaF-PET/CT compared with bone scintigraphy.

Diffusion-weighted magnetic resonance imaging (MRI) is a new MRI technology that provides functional information based on the limited diffusion of water in tumour tissue compared with normal tissue [2]. In DWI the tumour tissue appears as high-signal-intensity regions [6]. In this particular case not only multiple bone metastases were detected, but also extraosseous metastases to the lymph nodes.

Modern imaging offers a lot of possibilities, but also leaves us with a lot of questions. Can we rely on only one examination or are more examinations needed to make the right diagnosis? In this case a large number of bone lesions were detected in three different scanning techniques indicating a 100% likelihood of bone metastases. But what if only one of the examinations had shown 1-2 bone lesions? A bone biopsy might have been needed to make the diagnosis.