Justify and consider limitations of each imaging investigation selected to determine the presence and staging of suspected Prostate Cancer.

Justify and consider limitations of each imaging investigation selected to determine the presence and staging of suspected Prostate Cancer

A 65-year-old male patient with suspicion of prostate cancer will initially have a digital rectal examination (DRE) and a serum test for prostate-specific antigen (PSA) levels. An abnormal DRE and elevated PSA levels (>4ng/ml) indicates a prostate disorder (Yu and Hricak 2000). This suspicion has to be diagnostically confirmed to start appropriate treatment planning.

Trans-Rectal Ultrasound (TRUS) is the first line investigation; it produces high-resolution images by placing a high frequency transducer within the rectum (Yu and Hricak 2000). Lesions as small as a few millimetres (mm) can be seen (Cass 1992), however, TRUS cannot distinguish between benign and malignant lesions. Prostate cancer is commonly seen as a hypoechoic lesion in the peripheral zone (PZ), of the prostate gland. However, this appearance is not specific and only 40% of hypoechoic lesions are determined to be malignant. Appendix 1a shows the zonal anatomy of the prostate and the relationship of the PZ to the TZ. Tumours in the transitional zone (TZ) of the gland may be isoechoic, particularly when the patient has pre-existing benign prostatic hyperplasia (BPH), so identification of the tumour is difficult (Baxter et al. 1999). Hence, a TRUS-guided biopsy must be performed for histological diagnosis (Grainger and Allison 2001).

Power and Colour Doppler sonography provides TRUS with the potential for imaging tumour angiogensis through its ability to estimate tissue perfusion (Yu and Hricak 2000). Franco et al. (2000) suggest that power Doppler sonography should be routinely used complimentary to TRUS to improve the sensitivity in detecting prostate cancer.

Ultrasound is a safe method of imaging and uses no ionising radiation. It is a relatively inexpensive modality for imaging the prostate and is widely available in all NHS hospitals. TRUS is an invasive procedure and may not be acceptable to all patients. It is a non-sterile technique, so infection and septicaemia are serious complications and have to be prevented by appropriate antibiotic cover (Baxter et al. 1999). TRUS also has the limitation of being highly operator-dependant and dependant on the quality of the ultrasound equipment available (Littrup and Bailey 2000).

Sutton (2003) has concluded that ultrasound cannot evaluate lymph node enlargement on the pelvic sidewall or retroperitoneum and therefore Magnetic Resonance imaging (MRI) is the modality of choice in staging biopsy-proven prostate cancer. This has also been suggested by Grainger and Allison (2001) who add that: MRI can separately assess each Capsular, Seminal Vesicle and bladder involvement by tumour extension. Tumour detection is best on T2-weighted sequences. The PZ of the gland is seen as high signal intensity, the tumour will be seen as a focus of low signal within the PZ. Tumour extension outside the PZ into the TZ, which has an inhomogenous signal pattern, is difficult to detect on MRI. It prevents the differentiation of the tumour from BPH (Higgins and Hricak 1997). MRI also fails to detect microscopic disease and capsular invasion (Cheong and Krebs 2000). This is the T1 stage of the disease and is undetectable by DRE as well; see Appendix 1b for description of TNM staging classification.

A limitation of MRI post-biopsy is commonly from haemorrhage and oedema within the prostate gland occurred during biopsy. Haemorrhage artefacts and prostatitis make tumour detection very difficult in MRI (Sutton 2003). Higgins and Hricak (1997) recommend a delay of atleast 3 weeks between time of biopsy and MRI study, to allow the haemorrhage to clear.

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Yu and Hricak (2000) have found that the use of endorectal coil not only allows for high-resolution images but also the potential of acquiring metabolic information using magnetic resonance spectroscopy. This has also been suggested by Cheong and Krebs (2000) who add that spectroscopy could improve the sensitivity and specificity of MRI, expanding its diagnostic and staging usefulness. Alterations in levels of certain metabolites may provide prognostic information useful for treatment planning. Dynamic Contrast-enhanced MRI can also be used to demonstrate hypervascularity in prostate cancer (Ito et al. 2003).

The endorectal coil is often used in conjunction with a surface pelvic coil; this results in poor image quality of information received from the pelvic coil. This is because, as well as imaging anatomical structures within the pelvis, the endorectal coil is also imaged in situ, resulting in streaking artefacts on the image. When the endorectal coil is used on its own, there is less coverage of the pelvic area with the field of view limited to the prostate gland, seminal vesicles, bladder and close structures. However, the image resolution is very good. A study by Tewari et al. (2000) included 73 patients with biopsy- proven Prostate cancer who were examined by endorectal coil MRI. It concluded that the overall accuracy in defining local tumour stage was 82%, which suggests that endorectal MRI is an accurate method for local staging. Table 1 summarises the sensitivity and specificity found by the study.

Table 1: The sensitivity and Specificity of endorectal MRI (Tewari et al. 2000)

MRI has very good spatial resolution and tissue contrast. It has multiplanar capabilities and it does not use ionising radiation. MRI is an expensive modality and is of limited availability, with long waiting lists in NHS hospitals. The limitation of MRI equipment is that it can be claustrophobic for some patients. It is contraindicated for patients with metallic implants, pacemaker, neurostimulators, surgical clips, etc. (Grainger and Allison 2001). The use of an endorectal coil is invasive to the patient and the imaging time can exceed 35 minutes. Therefore, a good explanation of procedure must be given to patient to ensure their cooperation, and it is important for patients to keep very still during scanning.

Yu and Hricak (2000) have determined that “Computed Tomography (CT) is not recommended for local staging of prostate cancer due to its low diagnosing accuracy; 24% for extracapsular extension and 69% for seminal vesicle invasion”. Enlargement of the prostate gland is not indicative of cancer; it could be benign or malignant. If the carcinoma is within the capsule, causing enlargement, it cannot be differentiated from BPH (Yu and Hricak 2000).

Grainger and Allison (2001) argue that CT is highly accurate in advanced stages of the cancer, particularly in detection of metastases to lymph nodes, liver, lung and bone. It also demonstrates extraprostatic spread into adjacent organs. However, when looking for lymph node metastases, CT does not demonstrate the internal structure of the nodes. Therefore, microinvasions in normal sized nodes (<10mm) cannot be detected. This results in false negative results. Grainger and Allison (2001) recommend performing a percutaneous needle biopsy under CT-guidance in enlarged or suspicious nodes. This is also suggested by Yu and Hricak (2000); “Combined CT and CT-guided fine needle aspiration proves high specificity up to 100% for diagnosing lymph node metastases”.

CT is a relatively expensive modality. However, it is much cheaper than MRI and is widely available in most NHS hospitals. The scanning time is very short (<30seconds) and the procedure is much more acceptable to the patient. Its disadvantage includes the high skin dose from ionising radiation.

CT is excellent in distinguishing osteoblastic, osteolytic and mixed bony metastases. However, Grainger and Allison (2001) argue that CT should not be used to screen for bony metastases. Radionuclide Scintigraphy (RNS) is preferred as it examines the entire skeleton and is more sensitive at detecting small and early metastatic lesions.

Bruggmoser et al. (2003) state that bone Scintigraphy is not recommended for all prostate cancer patients, it should be routinely used for those cases with PSA >10ng/ml or with skeletal symptoms in the spine and pelvis. Tewari et al. (2000) reported that no patients in their study had a positive bone scintigram with PSA level <15ng/ml. Therefore, it can be suggested that RNI is performed with elevated PSA levels >15ng/ml.

Yu and Hawkins (2000) claim that RNS has a high sensitivity for bone metastases, but it has a low specificity. Radionuclide bone imaging is quick, relatively inexpensive and widely available (Love et al. 2003). The radiological appearance is of multiple sclerotic deposits. False positive results occur due to Paget’s disease and Osteoarthritis, which are prevalent in this age group (Merrick 1998). Love et al. (2003) suggest that Single Photon Emission Computed Tomography (SPECT) is useful in differentiating between metastases and Osteoarthritis in the spine. Sections of vertebrae can be examined on transaxial, coronal, sagittal and three-dimensional structures, which facilitates both localisation and characterisation of an abnormality. Yu and Hawkins (2000) suggest that plain films are useful, for selective bones, to evaluate inconclusive findings on the bone scan. False negative results can occur due to residual radioactivity in the bladder and underclothes, which can obscure parts of the pelvis (Merrick 1998).

In conclusion, TRUS-guided biopsy is the first line investigation to diagnose a suspected prostate cancer. MRI is used to stage biopsy proven carcinoma and evaluate ECE and SVI. CT can be used where MRI is contraindicated, or to evaluate spread in advanced stages >T3. RNS is used in advanced stages to evaluate bone metastases in patients with skeletal symptoms or PSA levels >15ng/ml. All these investigations have their limitations, but their benefits result in successful evaluation of prostate cancer, leading to the best method of treating the patient.

References

Baxter G M., Allan P L P., Morley P. (1999) Clinical Diagnostic Ultrasound. Blackwell Science.

Bruggmoser G., Mould R F., Tai T H P., Mate T P. (2003) Prostate Cancer Review. Zuck Schwerdt Verlag

Cass A S. (1992) Imaging of Urologic Disorders. Futura Publishing Co.

Franco O E., Arima K., Yanagawa M., Kawamura J. (2000) ‘The usefulness of power Doppler ultrasonography for diagnosing prostate cancer: histological correlation of each biopsy site’. British Journal of Urology, 85(9): 1049-52.

Grainger R G., Adam A., Dixon A K. (2001) Diagnostic Radiology – A textbook of Medical Imaging, 4th edition. Churchill Livingstone.

Higgins C B., Hricak H., Helms C A. (1997) Magnetic Resonance Imaging of the body. Lippincott-Raven Publishers.

Ito H, Kamoi K., Yokogama K., Yamada K., Nishimura T. (2003) ‘Visualisation of prostate cancer using dynamic contrast-enhanced MRI: comparison with trans-rectal power Doppler ultrasound’. British Journal of Radiology, 76: 617-624.

Littrup P J., Bailey S E., (2000) ‘Prostate Cancer: The role of TRUS and its impact on Cancer detection and management’. Radiologic Clinics of North America, 38(1): 87-113.

Love C., Din A S., Maria B., Tomas, Kalapparambath T P., Palestro C J. (2003) ‘Radionuclide bone imaging: An illustrated Review’. Radiographics, 23: 341-358.

Merrick M V. (1998) Essentials of Nuclear Medicine, 2nd edition. Springer.

Moss A A., Gamsu G., Genant H K. (1992) Computed Tomography of the body with Magnetic Resonance Imaging (2nd edition) W B Saunders Co.

Sutton D. (2003) Textbook of Radiology and Imaging, 7th edition. Churchill Livingstone.

Tewari A, Konety B, Bhandari A, et al. (2000) ‘Evaluation of the Patient With Prostate Cancer’. Medscape General Medicine 2(4):

Wong-You-Cheong JJ; Krebs TL. (2000) ‘MR imaging of prostate cancer’. Magnetic Resonance Imaging Clinics North America 8(4): 869-86.

Yu K K., Hawkins R A. (2000) ‘The prostate: diagnostic evaluation of metastatic disease’. Radiologic Clinics of North America, 38(1): 139-157.

Yu K K., Hricak H. (2000) ‘Imaging Prostate Cancer’. Radiologic Clinics of North America, 38(1): 59-85.

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Justify and consider limitations of each imaging investigation selected to determine the presence and staging of suspected Prostate Cancer.