26 Prostate Cancer

(1)

History

50-year-old male who is being evaluated because of a prevertebral soft tissue mass at T-9 on CT.

Findings

The intense 18-FDG activity at T-9 is seen on the sagittal images to involve both the prevertebral soft tissues and the vertebral body at T-9 (Figure 26.1.1). There is no oste- olysis and slight medullary sclerosis of this vertebral body. This appears on 18-FDG to be only one of many randomly scattered pathologically intense osseous foci (Figures 26.1.2 and 26.1.3). There is a small focus in the left ischium, involvement of the right subtrochanteric femoral medullary cavity (Figure 26.1.4), a small focus in the right anterior superior ilium, abnormal activity in the right proximal humeral diaphyses (Figure 26.1.5), and a possible small lesion near the right AC joint. Each of these lesions is characterized by slight sclerosis without osteolysis. The multiplicity of the lesions is indicative of likelihood for metastatic disease of unknown primary. Pertinent to this is the intense hypermetabolism in the posterior midline prostate gland (Figure 26.1.6).

If this proves to be prostate carcinoma with osseous metastasis at presentation, it would appear to represent an aggressive prostate lesion. Serum PSA is recommended as a ﬁrst initial step with subsequent prostate biopsy if positive.

Impression

The T-9 prevertebral soft tissue appears to represent coexistent involvement of the T-9 vertebral body as one of several scattered osseous metastases with slight sclerosis.

There is an intense midline posterior lobe prostate activity, consistent with an aggressive primary prostate carcinoma. Other diagnoses such as myeloma and lymphoma are considered less likely.

Pearls and Pitfalls

• 80% of expired prostate cancer patients have osseous metastases.

• The sensitivity of PET for prostate cancer is 50%.¹

• PET has a detection rate of 18% to 65% for metastatic disease.¹

26 Prostate Cancer

Hossein Jadvar

Case 26.1

264

(2)

FIGURE26.1.1. FIGURE26.1.2.

(3)

• PET imaging is a valuable tool for identifying lymph node metastases since it is a whole body exam.

• PET is currently useful in monitoring patient response to treatment for prostate cancer in patients with positive baseline examinations.³

Discussion

A problem with FDG imaging is that it does not accumulate well in some prostate cancers presumably due to a low glucose metabolic rate. Another problem with the tracer is that it is excreted in the urine which will potentially mask lesions in the vicinity of the prostate.

11C-choline may provide an alternative way for prostate cancer imaging. Choline is an important component of phospholipids in cell membrane integrity. Most prostate cancer display a high proliferation rate and increases production of cellular compo- nents for choline uptake. Choline may be superior than FDG because it does not accumulate in urine. The sensitivity of ¹¹C-choline PET and conventional imaging is 80%

vs. 47%, in histologically proven cases. The speciﬁcity is 96% vs. 98% and accuracy 93%

vs. 86%, respectively. Micrometastases and bowel activity are common reasons for a false-negative exam.

11C-acetate also may be useful in the detection of recurrent prostate cancer. It can accumulate in prostate cancer and has a sensitivity higher than that of FDG. A problem with this agent is that it can also accumulate in normal prostate gland and benign prostate hyperplasia. This may lower the speciﬁcity of this exam.

266 Part II Clinical Cases