link
Bookmarks
Imaging Approaches
Bryan R. Foster, MD; Ghaneh Fananapazir, MD, FSAR, FSRU, FSABI
To access 4,300 diagnoses written by the world's leading experts in radiology, please log in or subscribe.Subscribe

Renal Mass Evaluation

  • General concepts: Renal masses can be the cause of patient symptomatology but are often discovered incidentally on imaging. While the initial imaging can sometimes confidently diagnose the lesion, often additional imaging is required to characterize it as benign or of malignant potential. CT, MR, and US (especially with the advent of contrast-enhanced US) all play important roles in renal lesion characterization.
  • CT: CT is the most common imaging modality to characterize indeterminate renal lesions. A homogeneous lesion on NECT measuring -10 to 20 HU is highly likely to represent a cyst, while those > 70 HU represent a benign, hyperdense cyst. On portal venous-phase CT, cysts can confidently be diagnosed in the 21-30 HU range. Cysts that are simple can be considered benign, while those that are complex need to be evaluated further using the Bosniak classification. Renal lesions < -10 HU contain fat and almost always represent angiomyolipomas. Renal lesions between 20-70 HU need to be further evaluated. True enhancement (> 20 HU change between NECT and nephrographic phase) indicates a solid mass [renal cell carcinoma (RCC), oncocytoma, lipid-poor angiomyolipoma, metastasis, etc.]. Lack of enhancement (< 10 HU change) indicates a hyperdense cyst. Equivocal enhancement (10-20 HU change) may indicate pseudoenhancement of a cyst or mild enhancement of a solid mass and may benefit from contrast-enhanced US or MR, which are more sensitive in detecting true enhancement.
  • Dual-energy CT is gaining traction in characterizing renal masses using virtual monochromatic imaging. In addition to potentially obviating the need for a noncontrast phase, dual-energy CT potentially decreases pseudoenhancement.
  • MR: MR outperforms CT in the characterization of smaller lesions (< 1.5 cm) given its lack of pseudoenhancement as well as its high specificity for cysts on T2WI. Lesion enhancement on MR is more sensitive than on CT. In the case of an indeterminate renal lesion where the patient is unable to receive contrast, unenhanced MR may still be able to provide useful information, as a uniform, very high T2 signal lesion can be diagnosed as a cyst. Homogeneous high T1 signal also suggests a benign cyst. DWI may be useful in suggesting RCC from oncocytoma.
  • US: US has historically been relegated to the characterization of renal lesions based on whether or not they met the characteristics of a cyst: Anechoic, thin, well-defined wall, posterior acoustic enhancement, and no internal flow on Doppler imaging. However, with the emergence of contrast-enhanced US, previously indeterminate renal lesions can now be characterized as vascularized (indicating a solid mass) or not. Contrast-enhanced US is exquisitely sensitive, exceeding the sensitivity of CT and probably MR in detecting internal vascular flow, especially in patients where the kidney and the lesion are sonographically readily visible.

Hematuria Evaluation

  • CT urography (CTU): All patients with macroscopic hematuria should undergo CTU. Microscopic hematuria is a common problem and, while CTU is highly sensitive and specific for malignancy, historically the diagnostic yield of CTU for upper tract cancer is only ~ 1%. Recently updated guidelines by the American Urologic Association (AUA) risk stratify patients to decrease unnecessary imaging and increase yield; only those in the high-risk group should undergo CTU. All patients undergoing CTU for hematuria should also be referred for cystoscopy (typically performed after CTU). Therefore, detection of a subtle bladder mass by CTU is less important. CTU is performed primarily to detect upper tract cancers.
  • Many different techniques are used for CTU (number of phases, number and timing of boluses) with no consensus. Dose-reduction techniques include DECT, split bolus technique, and low kVp imaging. While the delayed phase is important to identify ureter filling defects, increasing evidence suggests that corticomedullary or nephrographic phase is equally important as urothelial carcinoma enhances avidly and can be detected readily on these earlier phases. Most institutions perform noncontrast, nephrographic, and delayed phases at a minimum. Oral hydration is the easiest patient preparation. Using IV hydration and IV Lasix, on the other hand, adds complexity with questionable benefit.
  • MR urography (MRU): While MRU is attractive because it avoids radiation, it is not widely utilized for hematuria. It is an appropriate modality in a patient unable to undergo CTU due to allergy or renal insufficiency. MRU is less sensitive for upper tract malignancy compared to CTU. Additionally, stones are poorly detected.
  • Intravenous urography, retrograde urography: Intravenous urography has been abandoned for CTU. Retrograde (or antegrade) urography remains important and is typically performed after CTU to confirm abnormalities and obtain biopsy or guide other interventions.
  • US: In some low-risk and all intermediate-risk groups with microscopic hematuria, renal and bladder US is appropriate in the work-up as it can detect stones, renal masses, and bladder lesions.

Kidney Graft Evaluation

  • US: US serves as the 1st-line imaging modality given the kidney graft's relative superficiality, need for repeat imaging, lack of radiation, and ability to assess anatomy as well as perfusion. Grayscale assessment of the kidney graft is used to evaluate for hydronephrosis as well as the presence of perigraft fluid collections. Color or power Doppler is used to assess for graft perfusion, and spectral Doppler looks at renal artery flow as well as intraparenchymal resistive indices. Perfusional assessment can be supplemented with the use of contrast-enhanced US.
  • CT: Perigraft collections may be difficult to fully evaluate by US, and CT may be useful to fully assess deeper collections. Iodinated contrast does not seem to confer any specific risks to patients with kidney grafts and should be used when clinically necessary. CTA can be employed to evaluate for the presence of vascular abnormalities, including transplant renal artery stenosis.
  • MR: MR can be utilized to evaluate for vascular abnormalities. Both unenhanced MR techniques, as well as contrast-enhanced MR, have been employed. The use of macrocyclic gadolinium agents has mitigated the concern for nephrogenic systemic fibrosis and can be used in patients with kidney grafts.

Adrenal Mass Evaluation

  • General concepts: Adrenal masses are common and most frequently represent benign adenomas. However, a subset represents adrenal cortical carcinomas, pheochromocytomas, and metastases. Therefore, correct follow-up and imaging play an important role in the balance between the overutilization of imaging and the underdiagnosis of clinically important adrenal masses. In general, lesions < 1 cm do not need to be pursued. Lesions > 4 cm usually require surgical evaluation. Those between 1-4 cm may require further imaging evaluation.
  • CT: CT serves as the main modality for assessing the adrenal gland. The presence of macroscopic fat can be seen in the setting of myelolipomas or, less commonly, in smaller quantities with lipomatous metaplasia with adrenocortical neoplasms. On NECT, If the adrenal mass measures ≤ 10 HU, a diagnosis of adrenal adenoma can be made with fair confidence (although cyst or pseudocyst would be in the differential). For those that have indeterminate characteristics on NECT (> 10 HU), further evaluation can be performed using contrast kinetics. Adenomas typically show brisk washout of contrast as opposed to metastases, which tend to retain contrast. However, a small percentage of pheochromocytomas can also show brisk washout, and clinical history may be important to avoid mischaracterization of adrenal masses. Dual-energy CT utilizing virtual monochromatic imaging has shown utility in diagnosing adrenal adenomas utilizing the 10 HU cutoff.
  • MR: Chemical shift MR is employed to identify the lipid content of adrenal adenomas and is useful to evaluate adrenal masses in patients with allergies to iodinated contrast.
  • PET/CT or biopsy: For patients with a history of malignancy and an enlarging adrenal mass, an indeterminate adrenal mass on adrenal CT, or an adrenal mass ≥ 4 cm, PET/CT or biopsy should be considered due to concern for metastatic disease.

Bladder Mass Evaluation

  • CTU: While CTU can be highly sensitive for bladder cancer, good technique is needed to opacify the bladder. However, since all patients with hematuria need to undergo cystoscopy based on current guidelines, CTU is not performed to detect bladder cancer, rather it is performed to detect an upper tract cancer, since this portion of the urinary tract is not readily accessible with a scope. CT does however play a role in bladder cancer staging by readily detecting nodal and distant metastases. CT is more limited in tumor stage evaluation. Advanced T3 or T4 disease may be detected by CT, but this is generally a pathologic diagnosis obtained by transurethral resection of bladder tumor (TURBT) through a cystoscope, a procedure that is diagnostic and potentially therapeutic.
  • MR: The role of MR for the local staging of bladder cancer continues to evolve. MR is highly accurate in local staging, particularly when multiparametric imaging is used (T2WI, DWI, and DCE sequences) and when combined with the Vesical Imaging Reporting and Data System (VI-RADS). However, prebiopsy MR prior to TURBT has not been adopted at many high-volume centers, and its future role is uncertain at this point.

Elevated PSA and Prostate MR

  • General concepts: Clinically significant prostate cancer is most commonly defined as Gleason score ≥ 7 (grade group ≥ 2). Most clinically significant cancer needs treatment, whereas small-volume, clinically insignificant cancer in patients with PSA < 10 may be able to avoid treatment and be placed on active surveillance. Multiparametric prostate MR (mpMR) and the Prostate Imaging Reporting and Data System (PI-RADS) are currently optimized to detect clinically significant cancer and have rapidly become the standard in imaging evaluation of the prostate.
  • Indications: Despite the increasingly recognized problem of prostate cancer overdiagnosis by PSA screening, most patients with significant prostate cancer are still detected due to abnormal PSA or digital rectal exam. Historically, imaging of the tumor within the prostate was not performed and only detected and quantified by transrectal US-guided (TRUS) biopsy obtaining ≥ 12 cores randomly from the prostate. mpMR has rapidly grown in the past 10 years and is now performed for many indications due to its high accuracy. mpMR is currently commonly performed in 4 scenarios, and it is important to understand each.
  • First, mpMR is being increasingly performed in men with elevated PSA who have not had a biopsy (so-called biopsy naive). This is being driven mainly by 2 factors; first, targeted biopsy of the prostate either by US fusion biopsy or in-bore biopsy techniques is increasingly available, and second, there is good evidence that MR-detected targets harbor the highest grade cancer, and targeted biopsy is more likely to detect clinically significant cancer compared to random TRUS biopsy. Various society guidelines have recognized this accumulating data and have made mpMR prior to biopsy and the targeted biopsy approach a recommendation.
  • The second common indication for mpMR is evaluation of men with elevated PSA who have had negative TRUS biopsy previously. TRUS biopsy misses ~ 30% of clinically significant cancer. Therefore, these men often harbor cancer readily detected by mpMR, classically in the anterior transition zone (TZ) or in the peripheral zone (PZ) apex, both locations that are undersampled by TRUS biopsy. Targeted biopsy of these lesions allows confirmation of cancer and the patient to undergo appropriate treatment.
  • The third common indication for mpMR is evaluation of men who have known prostate cancer but have chosen an active surveillance pathway. mpMR may be done at the outset of active surveillance to determine if there is a clinically significant tumor that would need targeted biopsy and preclude active surveillance. mpMR is also performed in these patients if PSA is rising or to follow-up known lesions for growth.
  • Finally, the fourth common indication for mpMR is local staging of prostate cancer in men about to undergo treatment, most commonly prior to robotic prostatectomy or image-guided radiotherapy. mpMR has reasonable accuracy to identify organ-confined disease (≤ T2) or extracapsular extension (≥ T3), and knowing this may alter treatment approach.
  • It is important to understand that mpMR however does not have perfect NPV. Thus, a negative mpMR, at this point, does not help men avoid TRUS biopsy.
  • Technical aspects: Adherence to excellent MR technique is crucial to maintain high accuracy in mpMR. This is because many cancers are small, and both high spatial resolution and high SNR is needed to depict these. PI-RADS has set forth minimal technical standards while allowing for flexibility across different MR systems and field strengths. When possible, mpMR should be performed at 3T. Endorectal coils, while not widely utilized, improve signal several fold and should be considered. mpMR is made up of 3 core sequences: T2WI, DWI, and DCE.
  • PI-RADS: The recent explosion of mpMR has in part been driven by PI-RADS, which provides a validated framework for interpretation and is designed to maximize detection of clinically significant prostate cancer. PI-RADS has gone through several iterations and is currently on version 2.1. PI-RADS assigns lesions into 1 of 5 categories based on the likelihood of clinically significant prostate cancer, similar to the models of LI-RADS and BI-RADS. A detailed and practical guide to PI-RADS interpretation is laid out in other chapters.
  • PI-RADS differentiates scoring whether a lesion is located in the TZ or PZ. In the TZ, T2WI is most important for scoring with DWI used as a tiebreaker in some cases. In the PZ, DWI is most important for scoring with DCE used as a tiebreaker. Despite updates and changes to the scoring system, portions of PI-RADS scoring are very much subjective. Several well-known pitfalls are laid out in subsequent chapters. Thus, radiologists need adequate, high-volume training and should recognize that there is a learning curve to reading mpMR. At many centers, prostate specialists interpret mpMR to maintain high accuracy. Radiologists should track their cases and correlate with biopsy results so that they become comfortable with what they are overcalling and undercalling. In the future, imaging center accreditation and radiologist certification with minimum cases may become widespread.
  • PET/CT: Concurrent to the growth of mpMR, PET/CT of prostate cancer has benefited from new radiotracers with higher sensitivity and specificity as compared to FDG. F-18 fluciclovine and PSMA are the two most common tracers in use which are prostate specific. Accumulating data indicates high sensitivity with these tracers, detecting sites of metastatic disease in biochemical recurrence, at very low PSA values. They are also sensitive and specific for showing lymph node and bone disease at initial staging, outperforming CT and MR and often significantly altering the treatment plan.
  • In the future, combined imaging approaches may become standard for some clinical scenarios. PET/MR units are increasingly being installed in academic centers and are appealing for rapid and complete anatomic and metabolic imaging diagnosis and staging of prostate cancer.

Selected References

  1. Waisbrod S et al: Assessment of diagnostic yield of cystoscopy and computed tomographic urography for urinary tract cancers in patients evaluated for microhematuria: a systematic review and meta-analysis. JAMA Netw Open. 4(5):e218409, 2021
  2. Weinreb JC et al: Use of intravenous gadolinium-based contrast media in patients with kidney disease: consensus statements from the American College of Radiology and the National Kidney Foundation. Radiology. 298(1):28-35, 2021
  3. Ahdoot M et al: MRI-targeted, systematic, and combined biopsy for prostate cancer diagnosis. N Engl J Med. 382(10):917-28, 2020
  4. Barocas DA et al: Microhematuria: AUA/SUFU guideline. J Urol. 204(4):778-86, 2020
  5. Lenis AT et al: Bladder cancer: a review. JAMA. 324(19):1980-91, 2020
  6. Walker SM et al: Positron emission tomography (PET) radiotracers for prostate cancer imaging. Abdom Radiol (NY). 45(7):2165-75, 2020
  7. Walker SM et al: Prospective evaluation of PI-RADS version 2.1 for prostate cancer detection. AJR Am J Roentgenol. 1-6, 2020
  8. Roberts JL et al: Diagnosis, management, and follow-up of upper tract urothelial carcinoma: an interdisciplinary collaboration between urology and radiology. Abdom Radiol (NY). 44(12):3893-905, 2019
  9. Turkbey B et al: Prostate Imaging Reporting and Data System Version 2.1: 2019 Update of Prostate Imaging Reporting and Data System Version 2. Eur Urol. 76(3):340-51, 2019
  10. Galgano SJ et al: Optimizing renal transplant Doppler ultrasound. Abdom Radiol (NY). 43(10):2564-73, 2018
  11. Herts BR et al: Management of the incidental renal mass on CT: a white paper of the ACR Incidental Findings Committee. J Am Coll Radiol. 15(2):264-73, 2018
  12. Fananapazir G et al: Sonographic evaluation of clinically significant perigraft hematomas in kidney transplant recipients. AJR Am J Roentgenol. 205(4):802-6, 2015
Related Anatomy
Loading...
Related Differential Diagnoses
Loading...
References
Tables

Tables

Renal Mass Evaluation

  • General concepts: Renal masses can be the cause of patient symptomatology but are often discovered incidentally on imaging. While the initial imaging can sometimes confidently diagnose the lesion, often additional imaging is required to characterize it as benign or of malignant potential. CT, MR, and US (especially with the advent of contrast-enhanced US) all play important roles in renal lesion characterization.
  • CT: CT is the most common imaging modality to characterize indeterminate renal lesions. A homogeneous lesion on NECT measuring -10 to 20 HU is highly likely to represent a cyst, while those > 70 HU represent a benign, hyperdense cyst. On portal venous-phase CT, cysts can confidently be diagnosed in the 21-30 HU range. Cysts that are simple can be considered benign, while those that are complex need to be evaluated further using the Bosniak classification. Renal lesions < -10 HU contain fat and almost always represent angiomyolipomas. Renal lesions between 20-70 HU need to be further evaluated. True enhancement (> 20 HU change between NECT and nephrographic phase) indicates a solid mass [renal cell carcinoma (RCC), oncocytoma, lipid-poor angiomyolipoma, metastasis, etc.]. Lack of enhancement (< 10 HU change) indicates a hyperdense cyst. Equivocal enhancement (10-20 HU change) may indicate pseudoenhancement of a cyst or mild enhancement of a solid mass and may benefit from contrast-enhanced US or MR, which are more sensitive in detecting true enhancement.
  • Dual-energy CT is gaining traction in characterizing renal masses using virtual monochromatic imaging. In addition to potentially obviating the need for a noncontrast phase, dual-energy CT potentially decreases pseudoenhancement.
  • MR: MR outperforms CT in the characterization of smaller lesions (< 1.5 cm) given its lack of pseudoenhancement as well as its high specificity for cysts on T2WI. Lesion enhancement on MR is more sensitive than on CT. In the case of an indeterminate renal lesion where the patient is unable to receive contrast, unenhanced MR may still be able to provide useful information, as a uniform, very high T2 signal lesion can be diagnosed as a cyst. Homogeneous high T1 signal also suggests a benign cyst. DWI may be useful in suggesting RCC from oncocytoma.
  • US: US has historically been relegated to the characterization of renal lesions based on whether or not they met the characteristics of a cyst: Anechoic, thin, well-defined wall, posterior acoustic enhancement, and no internal flow on Doppler imaging. However, with the emergence of contrast-enhanced US, previously indeterminate renal lesions can now be characterized as vascularized (indicating a solid mass) or not. Contrast-enhanced US is exquisitely sensitive, exceeding the sensitivity of CT and probably MR in detecting internal vascular flow, especially in patients where the kidney and the lesion are sonographically readily visible.

Hematuria Evaluation

  • CT urography (CTU): All patients with macroscopic hematuria should undergo CTU. Microscopic hematuria is a common problem and, while CTU is highly sensitive and specific for malignancy, historically the diagnostic yield of CTU for upper tract cancer is only ~ 1%. Recently updated guidelines by the American Urologic Association (AUA) risk stratify patients to decrease unnecessary imaging and increase yield; only those in the high-risk group should undergo CTU. All patients undergoing CTU for hematuria should also be referred for cystoscopy (typically performed after CTU). Therefore, detection of a subtle bladder mass by CTU is less important. CTU is performed primarily to detect upper tract cancers.
  • Many different techniques are used for CTU (number of phases, number and timing of boluses) with no consensus. Dose-reduction techniques include DECT, split bolus technique, and low kVp imaging. While the delayed phase is important to identify ureter filling defects, increasing evidence suggests that corticomedullary or nephrographic phase is equally important as urothelial carcinoma enhances avidly and can be detected readily on these earlier phases. Most institutions perform noncontrast, nephrographic, and delayed phases at a minimum. Oral hydration is the easiest patient preparation. Using IV hydration and IV Lasix, on the other hand, adds complexity with questionable benefit.
  • MR urography (MRU): While MRU is attractive because it avoids radiation, it is not widely utilized for hematuria. It is an appropriate modality in a patient unable to undergo CTU due to allergy or renal insufficiency. MRU is less sensitive for upper tract malignancy compared to CTU. Additionally, stones are poorly detected.
  • Intravenous urography, retrograde urography: Intravenous urography has been abandoned for CTU. Retrograde (or antegrade) urography remains important and is typically performed after CTU to confirm abnormalities and obtain biopsy or guide other interventions.
  • US: In some low-risk and all intermediate-risk groups with microscopic hematuria, renal and bladder US is appropriate in the work-up as it can detect stones, renal masses, and bladder lesions.

Kidney Graft Evaluation

  • US: US serves as the 1st-line imaging modality given the kidney graft's relative superficiality, need for repeat imaging, lack of radiation, and ability to assess anatomy as well as perfusion. Grayscale assessment of the kidney graft is used to evaluate for hydronephrosis as well as the presence of perigraft fluid collections. Color or power Doppler is used to assess for graft perfusion, and spectral Doppler looks at renal artery flow as well as intraparenchymal resistive indices. Perfusional assessment can be supplemented with the use of contrast-enhanced US.
  • CT: Perigraft collections may be difficult to fully evaluate by US, and CT may be useful to fully assess deeper collections. Iodinated contrast does not seem to confer any specific risks to patients with kidney grafts and should be used when clinically necessary. CTA can be employed to evaluate for the presence of vascular abnormalities, including transplant renal artery stenosis.
  • MR: MR can be utilized to evaluate for vascular abnormalities. Both unenhanced MR techniques, as well as contrast-enhanced MR, have been employed. The use of macrocyclic gadolinium agents has mitigated the concern for nephrogenic systemic fibrosis and can be used in patients with kidney grafts.

Adrenal Mass Evaluation

  • General concepts: Adrenal masses are common and most frequently represent benign adenomas. However, a subset represents adrenal cortical carcinomas, pheochromocytomas, and metastases. Therefore, correct follow-up and imaging play an important role in the balance between the overutilization of imaging and the underdiagnosis of clinically important adrenal masses. In general, lesions < 1 cm do not need to be pursued. Lesions > 4 cm usually require surgical evaluation. Those between 1-4 cm may require further imaging evaluation.
  • CT: CT serves as the main modality for assessing the adrenal gland. The presence of macroscopic fat can be seen in the setting of myelolipomas or, less commonly, in smaller quantities with lipomatous metaplasia with adrenocortical neoplasms. On NECT, If the adrenal mass measures ≤ 10 HU, a diagnosis of adrenal adenoma can be made with fair confidence (although cyst or pseudocyst would be in the differential). For those that have indeterminate characteristics on NECT (> 10 HU), further evaluation can be performed using contrast kinetics. Adenomas typically show brisk washout of contrast as opposed to metastases, which tend to retain contrast. However, a small percentage of pheochromocytomas can also show brisk washout, and clinical history may be important to avoid mischaracterization of adrenal masses. Dual-energy CT utilizing virtual monochromatic imaging has shown utility in diagnosing adrenal adenomas utilizing the 10 HU cutoff.
  • MR: Chemical shift MR is employed to identify the lipid content of adrenal adenomas and is useful to evaluate adrenal masses in patients with allergies to iodinated contrast.
  • PET/CT or biopsy: For patients with a history of malignancy and an enlarging adrenal mass, an indeterminate adrenal mass on adrenal CT, or an adrenal mass ≥ 4 cm, PET/CT or biopsy should be considered due to concern for metastatic disease.

Bladder Mass Evaluation

  • CTU: While CTU can be highly sensitive for bladder cancer, good technique is needed to opacify the bladder. However, since all patients with hematuria need to undergo cystoscopy based on current guidelines, CTU is not performed to detect bladder cancer, rather it is performed to detect an upper tract cancer, since this portion of the urinary tract is not readily accessible with a scope. CT does however play a role in bladder cancer staging by readily detecting nodal and distant metastases. CT is more limited in tumor stage evaluation. Advanced T3 or T4 disease may be detected by CT, but this is generally a pathologic diagnosis obtained by transurethral resection of bladder tumor (TURBT) through a cystoscope, a procedure that is diagnostic and potentially therapeutic.
  • MR: The role of MR for the local staging of bladder cancer continues to evolve. MR is highly accurate in local staging, particularly when multiparametric imaging is used (T2WI, DWI, and DCE sequences) and when combined with the Vesical Imaging Reporting and Data System (VI-RADS). However, prebiopsy MR prior to TURBT has not been adopted at many high-volume centers, and its future role is uncertain at this point.

Elevated PSA and Prostate MR

  • General concepts: Clinically significant prostate cancer is most commonly defined as Gleason score ≥ 7 (grade group ≥ 2). Most clinically significant cancer needs treatment, whereas small-volume, clinically insignificant cancer in patients with PSA < 10 may be able to avoid treatment and be placed on active surveillance. Multiparametric prostate MR (mpMR) and the Prostate Imaging Reporting and Data System (PI-RADS) are currently optimized to detect clinically significant cancer and have rapidly become the standard in imaging evaluation of the prostate.
  • Indications: Despite the increasingly recognized problem of prostate cancer overdiagnosis by PSA screening, most patients with significant prostate cancer are still detected due to abnormal PSA or digital rectal exam. Historically, imaging of the tumor within the prostate was not performed and only detected and quantified by transrectal US-guided (TRUS) biopsy obtaining ≥ 12 cores randomly from the prostate. mpMR has rapidly grown in the past 10 years and is now performed for many indications due to its high accuracy. mpMR is currently commonly performed in 4 scenarios, and it is important to understand each.
  • First, mpMR is being increasingly performed in men with elevated PSA who have not had a biopsy (so-called biopsy naive). This is being driven mainly by 2 factors; first, targeted biopsy of the prostate either by US fusion biopsy or in-bore biopsy techniques is increasingly available, and second, there is good evidence that MR-detected targets harbor the highest grade cancer, and targeted biopsy is more likely to detect clinically significant cancer compared to random TRUS biopsy. Various society guidelines have recognized this accumulating data and have made mpMR prior to biopsy and the targeted biopsy approach a recommendation.
  • The second common indication for mpMR is evaluation of men with elevated PSA who have had negative TRUS biopsy previously. TRUS biopsy misses ~ 30% of clinically significant cancer. Therefore, these men often harbor cancer readily detected by mpMR, classically in the anterior transition zone (TZ) or in the peripheral zone (PZ) apex, both locations that are undersampled by TRUS biopsy. Targeted biopsy of these lesions allows confirmation of cancer and the patient to undergo appropriate treatment.
  • The third common indication for mpMR is evaluation of men who have known prostate cancer but have chosen an active surveillance pathway. mpMR may be done at the outset of active surveillance to determine if there is a clinically significant tumor that would need targeted biopsy and preclude active surveillance. mpMR is also performed in these patients if PSA is rising or to follow-up known lesions for growth.
  • Finally, the fourth common indication for mpMR is local staging of prostate cancer in men about to undergo treatment, most commonly prior to robotic prostatectomy or image-guided radiotherapy. mpMR has reasonable accuracy to identify organ-confined disease (≤ T2) or extracapsular extension (≥ T3), and knowing this may alter treatment approach.
  • It is important to understand that mpMR however does not have perfect NPV. Thus, a negative mpMR, at this point, does not help men avoid TRUS biopsy.
  • Technical aspects: Adherence to excellent MR technique is crucial to maintain high accuracy in mpMR. This is because many cancers are small, and both high spatial resolution and high SNR is needed to depict these. PI-RADS has set forth minimal technical standards while allowing for flexibility across different MR systems and field strengths. When possible, mpMR should be performed at 3T. Endorectal coils, while not widely utilized, improve signal several fold and should be considered. mpMR is made up of 3 core sequences: T2WI, DWI, and DCE.
  • PI-RADS: The recent explosion of mpMR has in part been driven by PI-RADS, which provides a validated framework for interpretation and is designed to maximize detection of clinically significant prostate cancer. PI-RADS has gone through several iterations and is currently on version 2.1. PI-RADS assigns lesions into 1 of 5 categories based on the likelihood of clinically significant prostate cancer, similar to the models of LI-RADS and BI-RADS. A detailed and practical guide to PI-RADS interpretation is laid out in other chapters.
  • PI-RADS differentiates scoring whether a lesion is located in the TZ or PZ. In the TZ, T2WI is most important for scoring with DWI used as a tiebreaker in some cases. In the PZ, DWI is most important for scoring with DCE used as a tiebreaker. Despite updates and changes to the scoring system, portions of PI-RADS scoring are very much subjective. Several well-known pitfalls are laid out in subsequent chapters. Thus, radiologists need adequate, high-volume training and should recognize that there is a learning curve to reading mpMR. At many centers, prostate specialists interpret mpMR to maintain high accuracy. Radiologists should track their cases and correlate with biopsy results so that they become comfortable with what they are overcalling and undercalling. In the future, imaging center accreditation and radiologist certification with minimum cases may become widespread.
  • PET/CT: Concurrent to the growth of mpMR, PET/CT of prostate cancer has benefited from new radiotracers with higher sensitivity and specificity as compared to FDG. F-18 fluciclovine and PSMA are the two most common tracers in use which are prostate specific. Accumulating data indicates high sensitivity with these tracers, detecting sites of metastatic disease in biochemical recurrence, at very low PSA values. They are also sensitive and specific for showing lymph node and bone disease at initial staging, outperforming CT and MR and often significantly altering the treatment plan.
  • In the future, combined imaging approaches may become standard for some clinical scenarios. PET/MR units are increasingly being installed in academic centers and are appealing for rapid and complete anatomic and metabolic imaging diagnosis and staging of prostate cancer.

Selected References

  1. Waisbrod S et al: Assessment of diagnostic yield of cystoscopy and computed tomographic urography for urinary tract cancers in patients evaluated for microhematuria: a systematic review and meta-analysis. JAMA Netw Open. 4(5):e218409, 2021
  2. Weinreb JC et al: Use of intravenous gadolinium-based contrast media in patients with kidney disease: consensus statements from the American College of Radiology and the National Kidney Foundation. Radiology. 298(1):28-35, 2021
  3. Ahdoot M et al: MRI-targeted, systematic, and combined biopsy for prostate cancer diagnosis. N Engl J Med. 382(10):917-28, 2020
  4. Barocas DA et al: Microhematuria: AUA/SUFU guideline. J Urol. 204(4):778-86, 2020
  5. Lenis AT et al: Bladder cancer: a review. JAMA. 324(19):1980-91, 2020
  6. Walker SM et al: Positron emission tomography (PET) radiotracers for prostate cancer imaging. Abdom Radiol (NY). 45(7):2165-75, 2020
  7. Walker SM et al: Prospective evaluation of PI-RADS version 2.1 for prostate cancer detection. AJR Am J Roentgenol. 1-6, 2020
  8. Roberts JL et al: Diagnosis, management, and follow-up of upper tract urothelial carcinoma: an interdisciplinary collaboration between urology and radiology. Abdom Radiol (NY). 44(12):3893-905, 2019
  9. Turkbey B et al: Prostate Imaging Reporting and Data System Version 2.1: 2019 Update of Prostate Imaging Reporting and Data System Version 2. Eur Urol. 76(3):340-51, 2019
  10. Galgano SJ et al: Optimizing renal transplant Doppler ultrasound. Abdom Radiol (NY). 43(10):2564-73, 2018
  11. Herts BR et al: Management of the incidental renal mass on CT: a white paper of the ACR Incidental Findings Committee. J Am Coll Radiol. 15(2):264-73, 2018
  12. Fananapazir G et al: Sonographic evaluation of clinically significant perigraft hematomas in kidney transplant recipients. AJR Am J Roentgenol. 205(4):802-6, 2015