Assessment of primary tumor (T)
The T category describes the primary lesion. Clinical staging (cT) is determined prior to treatment, while pathological staging (pT) is established after surgery based on the examination of resected tissues.
- T1: The tumor is not clinically apparent (not palpable and not visible on imaging). It is found incidentally upon removal of prostate tissue (T1a — occupying 5% or less of the resected volume, T1b — greater than 5%) or via needle biopsy performed due to an elevated PSA level (T1c).
- T2: The neoplasm is confined within the prostate tissues. In the clinical classification, it may involve up to half of one lobe (T2a), more than half (T2b), or both lobes (T2c). In the pathological version (pT), all these substages are grouped into category pT2 (organ-confined tumor).
- T3: The lesion extends through the prostatic capsule. Stage T3a indicates extracapsular extension (including microinvasion into the bladder neck). Stage T3b indicates direct invasion into the seminal vesicles.
- T4: The tumor is fixed or tethered to adjacent structures (other than the seminal vesicles). This may involve the external sphincter, rectum, levator ani muscles, and/or pelvic wall.
Lymph node involvement (N) and metastases (M)
The spread of tumor cells via the lymphatic and circulatory systems determines the prognosis of the disease.
Regional lymph nodes (stage N1 when involved) are defined as those lying below the bifurcation of the common iliac vessels. These include pelvic, internal iliac, hypogastric, and sacral nodes. If lymph nodes above this level (e.g., aortic, common iliac) or in other areas (inguinal, supraclavicular) are involved, it is classified as distant metastasis — stage M1a.
Distant metastases are divided into three groups:
- M1a: Metastases to non-regional lymph nodes.
- M1b: Skeletal bone involvement.
- M1c: Metastases to other organs (visceral). These are extremely rare at initial diagnosis. Hematogenous spread to the lungs, liver, adrenal glands, or brain is characteristic of advanced stages or specific aggressive subtypes of cancer.
Diagnostic imaging and staging
Primary clinical staging often utilizes nomograms incorporating digital rectal examination findings, serum PSA levels, and the Gleason score. This allows for calculating the probability of extracapsular extension, but does not show the exact location of the lesion. MRI is used for this purpose.
MRI Staging Technique The procedure requires acquiring high-resolution T2-weighted images (512 matrix), thin slices (approximately 3 mm), and a small field of view. Scanning is performed in at least two planes.
Signs of Extracapsular Invasion (from early to late):
- Broad tumor contact with the capsule.
- Local bulging of the capsular contour.
- Alteration of the normal MR signal from the capsule.
- Irregularity or blurring of the prostate contour.
- Infiltration of the surrounding periprostatic fat and obliteration of the rectoprostatic angle.
- Presence of visible tumor nodules in the periprostatic fat.
Signs of Seminal Vesicle Involvement: The process begins with focal or diffuse wall thickening of the vesicle. Subsequently, a mass appears within the lumen, the prostato-vesicular angle is obliterated, and in later stages, the architecture of the seminal vesicle is completely destroyed.
For detecting bone metastases, whole-body MRI (wb-MRI) with diffusion-weighted imaging (DWI) surpasses conventional scintigraphy and CT in specificity. The difference in the apparent diffusion coefficient (ADC) between healthy bone marrow and the tumor lesion serves as a reliable biomarker of therapeutic response. DWI and dynamic contrast-enhanced (DCE) sequences also aid in assessing the primary lesion, enabling earlier detection of contrast enhancement in involved seminal vesicles.
To remember the difference between T3 and T4: stage T3 is "roommates" (the tumor has breached the capsule or affected the seminal vesicles), while T4 is "going outside" (invasion into the rectum, sphincter, or pelvic muscles).
Class and exam questions
What is the difference between stages N1 and M1a?
N1 denotes metastases to pelvic lymph nodes located below the common iliac vessels. If nodes above this level (such as aortic) or inguinal nodes are involved, it is considered distant metastasis — stage M1a.
Why are clinical nomograms needed if we have MRI?
Nomograms combine the PSA level, Gleason score, and physical examination data to mathematically calculate the risk of extracapsular extension. They are useful for initial evaluation of progression probability prior to receiving high-resolution MRI results.
Which imaging modality best detects bone metastases?
Whole-body MRI with diffusion-weighted imaging has higher specificity compared to traditional bone scintigraphy. Additionally, it allows the use of the apparent diffusion coefficient (ADC) to evaluate treatment response.
What else to study on this topic
- Anatomic boundaries of regional and non-regional lymphatic drainage pathways of the pelvis
- Physical principles of DWI and DCE image formation in pelvic MRI
- Prognostic nomograms: principles of invasion risk calculation
- Utilization of the apparent diffusion coefficient (ADC) as a biomarker of tumor treatment response
- Algorithms for additional instrumental workup in patients with suspected visceral metastases
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Other topics in the section "Diagnostic Radiology of the Abdominal Organs"
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