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Prostate Imaging Basics
Resident Academic Half-DayOctober 2, 2012
Rebecca Hibbert, MD, FRCPC
Outline
• Anatomy
• Relevant concepts
• Biopsy
• Prostate Ca – imaging with US and MRI
• Other disease processes of the prostate and seminal vesicles
Anatomy
• Radiologically relevant:– Central and peripheral gland– Base, mid, and apex (sextants)– Right and left
Relevant Concepts
• Serum PSA > 4 ng/mL is abnormal.
• 95% of prostate cancers are adenocarcinomas• 70% arise in peripheral zone• 30% arise in central gland (20% in transition zone, 10% in
central zone)
• Nearly one third of biopsy-proven prostate cancers present with normal PSA levels
• 70–80% of patients with elevated PSA levels do not have prostate carcinoma
Relevant Concepts
• Local or regional disease • 5-year survival of 100%
• With distant metastases • 5-year survival drops to 34%
• Variety of treatment options – watchful waiting– hormonal treatment– radical prostatectomy (open, laparoscopic, or robotic) – various forms of radiation therapy (including external
beam and brachytherapy)– combined approaches
Gleason Score
• Score < 6• Well-differentiated cancers• Good prognosis
• Score 8-10• Worst prognosis• Highest risk of recurrence
• Score 7• Variable prognosis• Indeterminate risk of recurrence
Biospy
• Ultrasound has poor sensitivity for visualizing prostate Ca
• Sextant approach is therefore used– At least 10 cores advocated to minimize sampling errors– At TOH: 10 cores (5 right, 5 left), 18 gauge, 2 cm throw
• 2 in base (medial and lateral) on each side• 2 in mid (medial and lateral) on each side• 1 in apex on each side
– Can add cores if nodule is seen on US• AdenoCa hypoechoic
MRI – Normal appearance
• Peripheral zone high T2 signal intensity• Capsule rim of low T2 signal• Central gland intermediate T2 signal intensity
(more compact smooth muscle and sparser glandular elements)
• Neurovascular bundles course posterolateral to prostate capsule bilaterally at 5- and 7-o’clock
Role of MRI
• Staging high risk patients
• Evaluating rising PSA in post-prostatectomy patients in the absence of disease elsewhere
• Pre-ablation planning (cryotherapy)
MRI Technique
• Current clinical standard is to perform prostate MRI using endorectal and pelvic phased array coils on a magnet that is at least 1.5 T.
• Endorectal coils and high-resolution images are necessary for accurate localization and staging of prostate cancer
• 8-10 week wait between biopsy and MRI is recommended• Postbiopsy hemorrhage can distort image quality and
mask tumor
MRI Technique
• T1W images from aortic bifurcation to pelvis • to check for postbiopsy hemorrhage • to check for metastases to bone and lymph nodes
• Multiplanar high-resolution fast spin-echo (FSE) T2-weighted images
• Enables detection and localization of tumor
• Diffusion weighted imaging (DWI)• improves detection and localization• higher b values (1000–2000 s/mm2) are better
• 3D gradient echo unenhanced and multiphase contrast-enhanced images
MRI – Prostate Ca appearance
• Adenocarcinoma• Low T2 signal intensity, easily distinguished from the normal
high-signal peripheral zone• Restricted diffusion (high signal on DWI and low signal on ADC
map)• Rapid contrast enhancement and washout (like breast Ca)
• DDx for low T2 signal in peripheral zone• Adenocarcinoma• Biopsy-related hemorrhage (look for high T1 signal)• Prostatitis• Changes of hormone therapy• Postradiation fibrosis
Signs of Extracapsular Extension
• Asymmetric prostate capsular bulge with irregular margins
• Obliteration of the rectoprostatic angle• Asymmetry of neurovascular bundle• Tumor encasement of the neurovascular bundle• Seminal vesicle invasion
Seminal Vesicle (SV) Invasion
• Diagnostic Criteria:– Loss of normal SV architecture – SV enlargement with a low-signal-intensity mass on
T2-weighted images
• Caveat– After radiation, chemo or hormonal therapy, the SVs
often demonstrate decreased size, diffuse wall thickening, or diffuse low signal intensity on T2-weighted images. Can mimic tumor invasion.
Other disease processes
• Infection/inflammation– Prostatitis or seminal vesiculitis– Abscess (prostate or SVs)
PATH: areas of necrosis and presence of fungal forms (yeast, hyphae, and pseudohyphae) consistent with Candida species.
Cystic prostate masses
• Utricular cyst• Communicates with prostatic urethra • May contain spermatozoa• Confined within prostate at the midline• Associated with GU abnormalities (hypospadias,
cryptorchidism, unilateral renal agenesis)
• Müllerian duct cyst • Does not communicate with urethra • May extend above the prostate• Not associated with other abnormalities
From: Kim B, Kawashima A, Ryu J, Takahashi N, Hartman RP, and King BF. Imaging of the Seminal Vesicle and Vas Deferens. Radiographics. July 2009, 29, 1105-1121.