Introduction to Nephrology Diagnostic Imaging PDF

Nephrology and Urology Capatano – Radiology – Lesson 01: Introduction to Nephrology Diagnostic Imaging 10/10/2024 – Group #17(Giulia Dani and Anna Ghenciu) We open with a clinical case: 65-year-old patient, ma...

Nephrology and Urology Capatano – Radiology – Lesson 01: Introduction to Nephrology Diagnostic Imaging 10/10/2024 – Group #17(Giulia Dani and Anna Ghenciu) We open with a clinical case: 65-year-old patient, male. Symptoms: abdominal pain, urinary retention, fever, leukocytosis What would you ask for as the 1st imaging modality? In this case for the 1st level method of imaging we could choose between Ultrasound and X-ray. The doctor asked for an X-ray (but the professor would have asked for an ultrasound). Abdominal X-ray: What’s strange? 🡪 Central-posterior view We can see the lumbar spine, the ribs and all the soft tissue. The rendering of the soft tissue is bad here, for this reason the professor would have asked for an ultrasound. An hyperdense structure is recognizable in the left flank. Consequently, the patient also underwent an ultrasound and stones(=lithiasis) were found. Hydronephrosis is also present. An X-ray is performed instead of an ultrasound because there is air in the bowel, so it is easier to rule out other causes due to bowel obstruction. The lighter spots due to lithiasis are indicated in the picture. Ultrasound gives a better depiction of the morphology of the kidneys and the urinary tract. The 1st image here on the left represents the right kidney, the 2nd the left one: in the latter stones are seen as hyperechoic structures (indicated by the arrow). Ultrasonography(ultrasound) uses sound waves of frequencies 2 to 17 MHz (audible sound is in the range of 20 Hz to 20 kHz). Like SON R, images result from the propagation of sound waves through the body and their reflection from interfaces within the body. The time it takes from the sound waves to return to the transducer provides information on the position of the tissue in the body. 1 It doesn’t use ionizing radiation but uses sound waves to visualize structures. For this reason, it is very operator dependent. Cannot penetrate bone. At this point, a 2nd imaging modality is needed to better assess where the stones are and how much the kidney is suffering: Uro-CT Uro-CT is a very particular application of computed tomography, essential in evaluating the obstruction and renal function since 1st level imaging is limited in looking for ureters. Here 2 phases are seen: - CT without contrast - Urographic phase So, as 1st level imaging X-ray is performed, and as 2nd level CT and MRI. In the image above two phases can be seen: CT without contrast Urographic phase CT-computed tomography: cross-sectional modality with capabilities for multiplanar reconstruction and dynamic imaging to assess vascularity. The tube rotates around the body and a circle of stationary detectors catch penetrating X-rays, forming an image. The fundamental steps to follow are: - Initial diagnosis - Detection (site, volume, morphology) - Characterization - Disease balance - Staging - Therapeutical planning - Follow up - Response to therapy Urinary (or excretory) system: Located in the retroperitoneal area, it comprises kidneys, ureters, bladder, urethra. It can be studied by performing: X-ray (excluding ureters) Conventional urography CT urography MR urography 2 Ultrasound: 1st level exam of choice for the detection of primary lesions of the kidney (cystic/solid), calculi (upper – kidney - & lower – bladder urinary tract), and trauma. Some important signs you can find in the ultrasound are dilation duct and hyperechoic structures, but we don't have a good visualization of the ureters. Some images of cases obtained with US: Ultrasound is useful also under the interventional point of view: 3  Normal kidney ultrasound: normal adult renal length is between 9 and 12 cm (depending on the patient’s characteristics, such as age and BMI). There may a dimension difference between the two kidneys, normally of less than 1.5 cm. The kidneys should be seen as smooth in outline; the parenchyma surrounds a central echodense region, known as the central echo complex (the renal sinus), consisting of the pelvicalyceal system, together with the surrounding fat and renal blood vessels. Normal ureters are not usually visualized due to overlying bowel gas. The patient has to drink water at least 30 minutes before doing the ultrasound to have a good echoic window for the bladder. The ureters can be depicted in the intramural part of the bladder (white arrows drawn in the image to the left). The urinary bladder should be examined in the distended state: the walls should be sharply defined and barely perceptible. The bladder may also be assessed following micturition, to measure the post-micturition residual volume of urine. X-Rays: The four basic densities are: Air is the 1st one: black Soft tissue Fat Bone is the 4th one: white In between a scale of grays can be seen. Below are X-rays done with contrast. When there is no pathology of the kidney, to find kidneys location the lumbar spine between L1-L3 may be used. In the flank we can see the area where the kidneys are, and from these imagine where the ureters are and end up in the bladder. The technician can also change the TW to highlight the kidneys (as well as liver and spleen). 4  AP abdomen of a female patient on the left and of a male on the right. She skipped the slides about conventional tomograms. 5 Urography is a combined morphological and functional assessment of the urinary tract due to the presence of a contrast agent. The iodine contrast agent is administered by intravenous injection so that we wait that is passes through the kidneys to be then eliminated via the urinary tract. This way the dynamic phases can be seen by acquiring different frames at different timings: With contrast in the cortex With contrast in the pelvis Through the ureters with contrast to the bladder In the case in which some kind of lesion or pathology is present, a plus and a minus image can be seen: if a stone is present, a minus image appears as the contrast cannot enhance that zone; if instead the contrast flows with no problem, the image is plus. The contrast can be also given directly percutaneously or trans-nephrostomic (typically used to assess conditions of nephrostomy) in direct urography. Or the contrast can be directly put inside the bladder(cystogram) to dynamically assess the presence of obstruction in the bladder or urethra. Typical timings of urography: - Immediate film: before contrast - After 5-15 minutes (from contrast administration) film: Nephrogram phase - 30 minutes film: Ureterogram phase - 45 minutes film: Cystogram phase - Postvoiding film (=after urination) 6 CT Urography CT urography is a way to study the urinary system with CT. It is used for a comprehensive evaluation of the excretory system evaluation. Axial CT with thin collimation for excretory phase (High-resolution dataset) and (multiplanar recon). There is diffusion due to the advent of MDSCT. Axial view, with and without contrast. Contrast medium adds precision to the cortex. 7 CT urography: Protocols single bolus - triple phase 1. Pre-contrast: it helps us to visualize: i. Lithiasis ii. Calcifications iii. HU of solid lesion iv. Hemorrhage When contrast is administered intravenously, we can acquire the: 2. Nephografic face of superior abdomen: we use single bolus (100-150 ml, 2-4 ml/sec). The contrast in in the cortex, so we can assess: 1. Renal parenchyma 2. Masses 3. Flogosis ii. Arterial phase is the first phase just after contrast administration, when contrast medium passes through the arteries: cortex is very bright iii. parenchymal phase is the second phase with the contrast medium passing through the cortex 3. Then we wait from 9 to 12 minutes for the contrast to reach the bladder (if an obstruction is present, we could have to wait up until 20 minutes) to reach the excretory phase (to see ureters and bladder very well) a. Slice thickness < 3 mm (very thin because we need to do the 3D reconstruction), slice overlap 50% voxel isotropic for 3D reformatting CT Urography: excretory phase 3D recon 8 These are the 3D reconstruction that mimic an interventional study to better define the presence of pathologies in the urinary system. This is the most important imaging modality for kidneys. Clinical indications of CT urography: Example case: contrast picture, on the axial plane, representing the left kidney. It’s possible to see a kidney stone which causes hydronephrosis: kidney stones located in the 3rd part of the ureter (bigger than normal) can only be seen by CT Urography (and maybe X-ray). Apart from kidney stones, on other occasions, we could be able to visualize malformations, vascular abnormalities, solid and neoplastic masses. This is a CT urography: it represents an excretory phase since all the contrast is in the pelvis, a minus image, which represents a non-calcified calculus. We can also use CT urography to study the bladder and the presence of masses within it. 9 Magnetic Resonance Imaging (MRI): imaging technique that uses non-ionizing radiation to create tomographic diagnostic images that can be oriented on any spatial plane. MRI relies on the application of magnetic fields and radiofrequency waves. It was born to better define the soft tissue characterization (in fact it is the best imaging methodology in doing that) without using ionizing radiation. The techniques of MR in the particular urography settings are called: Pyelography (MRI U t2) or Urography with Contrast Enhancement (MRI U t1). The main difference is the use of a contrast medium in Urography (and NOT in Pyelography). In MR Pyelography we have T2-weighted images with great magnification of static fluids (water) and the urine itself serves as a contrast agent: there is no need to add contrast medium or radiation. It is used to the investigate the morphology of the excretory system, collecting system dilations, obstruction site and in pregnancy and pediatric population. In urography, instead, T1-weighted images are used; this technique allows us to better visualize anatomical 3D images with the use of a contrast agent (3D GRE🡪Gadolinium ev) and therefore to make functional (GFR) and dynamic evaluations (in the excretory phase). It doesn’t detect dilations of the collecting system. Pyelography is much more used than Urography. To administer the contrast agent in a patient we always have to make sure that s/he has a valid creatinine value, which reflects kidney function. To summarize all the methods: ultrasound is the 1st choice, CT Urography is the 2nd choice (needed most of the time), MRI is the 3rd choice (in particular Pyelography), especially when radiation can’t be used. MRU=magnetic resonance urography MRP=magnetic resonance pyelography 10 Urinary tract malformations and diseases: renal dysmorphisms and parenchymal malformations are commonly seen during CT (but also during Ultrasound abdominal evaluations), with an incidence of 1/500 adults, mainly displayed by male. Horseshoe kidneys: the kidneys fuse together at the bottom and assume a horseshoe shape (U shape). Usually discovered because in ultrasound the end of each kidney cannot be found, with the confirmation given by further CT examination. They are typically asymptomatic and an incidental finding (typically called an incidentaloma). they can also be associated with several complications and clinical conditions, which include: hydronephrosis, presence of renal calculi, increased susceptibility to traumas, infections, and increased incidence of malignancy (transition cell carcinoma of the renal pelvis) and increased incidence of renal vascular hypertension. Renal Ectopia: condition characterized by an abnormal localization of the kidney: lumbar kidney, a pelvic kidney, etc. Renal Agenesis is the congenital absence of one (1/500 births) or both(classic Potter syndrome) kidneys; usually visualized during Ultrasound evaluations. If bilateral it is usually fatal, instead, unilateral agenesis still allows the patient to have a normal life expectancy. Unless identified on antenatal screening, it is incidentally found when the abdomen is imaged for other reasons. Occasionally patients with unilateral renal agenesis develop secondary hypertension. Primary Megaureter: basket term to encompass causes of enlarged ureter which are intrinsic to it, rather then as a result of more distal abnormalities. It comprises: - Obstructed primary megaureter - Refluxing primary megaureter (although vesico-ureteric reflux [VUR] is a cause of primary congenital megaureter it is usually considere separately) - Non-refluxing unobstructed primary megaureter: diagnoses in the absence of reflux, structure, calculus or uterocele. Hydronephrosis is due to an obstruction in the urinary tract, which causes an increase in pressure and subsequent enlargement of kidneys, which in turn press against nearby organs. If this condition is left untreated, the kidney will eventually lose its function. Hydronephrosis is mainly detected with 11 Ultrasound, but also with CT: first-grade hydronephrosis is associated with pelvis dilation, second-grade with pelvicalyceal system dilatation (dilation of major calyces), 3rd grade with cortical thinning (also minor calyces are dilated, but still parenchyma is spared). Lastly, fourth-grade hydronephrosis is considered an emergency since parenchyma is compromised, the cortex cannot be seen anymore and therefore nephrostomy must be performed. With grade 1 and 2 usually we keep the patient under control, and we wait before intervening. This is the appearance of a CT imaging of nephrosis: grade 3 looks like a multicystic disease. Nephrostomy was first described in 1953; it is an intervention of radiological application, mainly performed in case of urinary obstruction secondary to calculi, urinary fistula, and decompression of perinephric fluid collections. It can be formed via ultrasound or fluoroscopy. The main causes of obstructions in the collecting system are calculi, tumors or previous surgeries. In the non-contrast acquisition, it is very difficult to distinguish between stones and phlebolites, which just look as hyperdense spots on imaging. Nephropathies are mainly investigated by CT. Ultrasound role in this setting is limited, because it is insensitive to the change in acute phase. So many patients sent from ER to ultrasound appear totally normal. That’s why we also ask for a CT: we see a reduced enhancement (precocious sign of kidney infection) with a typical focal wedge-like lesion in the cortex of the kidney that appear swollen and demonstrate reduced enhancement compared to normal portions of the kidney without contrast. The periphery of the cortex is also affected, helpful in distinguishing acute pyelonephritis from a renal 12 infarct (tends to spare the periphery, called rim sign). Other signs are reduction of kidney dimensions in the chronic phase infection (chronic pyeloneohritis). Pyelonephritis is a heterogenous group of upper urinary tract infections associated with inflammation of renal calyces, renal pelvis, and renal parenchyma. CT is mainly used to detect pyelonephritis since Ultrasound is insensitive to changes in acute pyelonephritis: there is a reduced enhancement (compared to normal portions of the kidney) and one/more swollen focal wedge-like regions. Possible features include: particulate matter/debris in the collecting system, reduced areas of cortical vascularity by using power Doppler, gas bubbles and abnormal echogenicity of the renal parenchyma. This is an example of Chronic Pyelonephritis, staged with US or CT: we can see a volumetric reduction of the kidney and a hyperechoic (since it’s fibrotic) cortical scar Renal focal lesions: renal masses Renal masses are incidentalomas (found out by accident) in most cases on US, CT, MR. Almost all the time, they are simple cysts, but in 5% of cases they are solid masses. This needs to be considered, given that 86% of solid masses proves to be aggressive tumors. Size, shape, margins, structure, localization have to be investigated. From the clinical point of view, we can divide the renal masses into: Non surgical masses Angiomyolipoma Oncocytoma Pseudotumor Lymphoma Surgical masses Renal carcinoma Transitional carcinoma Complex cystic lesions (usually requiring follow-up) Non- surgical masses: Angiomyolipoma is the most common benign solid renal lesion. It is usually a well-defined and heterogeneous tumor, typically located in the renal cortex and containing areas of fat (density on CT < 0, usually -20). It can be associated with other pathologies such as tuberous sclerosis, VHL and NF1, but most of the time it is just sporadic, with a prevalence in women (4:1). Most times are completely asymptomatic, so they are accidental findings. There may be calcification and necrosis, 13  but it is very rare. As the name suggests, the main characteristic is the presence of an adipose component and of a vascular component. They can, sometimes, bleed: the most dramatic picture is Wunderlich syndrome, which leads to hypovolemic shock due to the massive hemorrhage. In the US most of them are hyperechoic due to the composition and, if you perform CEUS, they can present peripheral enhancement. In clinical practice, when we suspect this kind of lesion, we ask for a CT to be sure of the diagnosis, as it will reveal the fatty density. In MR we use particular in- and opp- sequences, suppressive techniques, which show the pathognomonic india-like artifact. It is made up of 3 components: fat, muscle, vessels. This is a small lesion, probably asymptomatic, unilateral. In patients affected by tuberous sclerosis, it can be bilateral. In this CT, anteriorly to the kidney we see a very big mass, with different densities inside: the darker region is fat and a more solid region, seen in the arterial phase, which is blood. So, this is an AML causing bleeding. The risk of bleeding with this lesion is not huge, but it tends to increase together with the size of the masses. Oncocytoma is the second most common finding of renal masses (also an incidentaloma). It represents the 5% of adult renal neoplasm and its peak of occurrence is typically at 55 years old. It is more prevalent in male (2:1). They appear as sharply demarcated lesions with uniform enhancement at CT and often have a central scar, which is pathognomonic and used to distinguish this lesion from others, for instance renal carcinoma. Most of them are asymptomatic, but if symptomatic, it can lead to hematuria and pain in the flank. Calcifications in an oncocytoma can be present but are rare. At US it appears as a well-circumscribed isoechogenic mass. In CT it appears as a well-circumscribed, homogeneous attenuation with homogeneous enhancement and with a central stellate non-enhancing scar. In MR it appears hypointense on T1W and hyperintense on T2W (with hypointense scar if present). The tumor is usually solitary, 2-12 cm in diameter, but can be multifocal and bilateral. Surgical masses The most common subtype is the renal cell carcinoma. Renal cell carcinoma (RCC) is a typical ball-type lesion, starting from the cortex and extending toward the surrounding tissue. 50% of RCCs are incidental findings on imaging studies performed for non-urinary tract symptoms, so they are often asymptomatic. Peak incidence of RCC is between 60 and 70 years. RCC is associated with hereditary syndromes, such as von Hippel-Lindau, tuberous sclerosis and Birt-Hogg-Dubé. The most common subtype of RCC is clear cell carcinoma, followed by papillary and chromophobe RCC, then collecting duct carcinoma and finally medullary carcinoma. 14 Clear cell carcinoma (70-80% of RCCs) It can sometimes be cystic (15%, makes diagnosis harder). It can have a capsular infiltration and sometimes an involvement of the renal vein, and even IVC. Metastases spread mainly to the lung, then bone, liver and eventually soft tissue and pleura. At cell histology, glycogen and intracytoplasmic lipids can be seen. With US, in the inferior portion we see an exophytic mass, mixed, with an anechoic part, possibly necrosis, and a solid part. It gives pain and hematuria in 50% of cases. Again, usually US gives a very aspecific idea, so we tend to ask for a second choice imaging modality, a CT. A typical feature of clear cell carcinoma is strong enhancement in the arterial phase, but it may be difficult to see as all the cortical portion of the kidney has a strong enhancement in this phase. The nephrogenic phase is therefore the most sensitive phase for the detection of these lesions, as the renal parenchyma enhances homogeneously and more intensely than the tumor. The role of CT is significant not only for diagnosis but also for TNM of the pathology and the follow-up during the treatment. For instance it can show the presence of metastases and infiltrations in other organs and structures. You can also see in it some calcifications, fat, hemorrhage, necrosis, cystic components. It's a really mixed lesion with high enhancement. CT is fundamental for the planning of the surgery (and try to save healthy tissue if possible), and for the follow-up. In MR clear cell carcinoma appears iso-hypointense in T1 and iso-hyperintense in T2. After contrast media administration It typically has inhomogeneous enhancement, useful to distinguish it from other renal masses. Papillary carcinoma Papillary carcinoma accounts for 10-15% of all RCCs, being the second most common type. These lesions are typically homogeneous and hypovascular and can therefore mimic cysts. Bilateral and multifocal tumors are more frequently seen in papillary RCC than in other types of RCC. The 5-year survival is 80-90%. They have a slightly increased male predilection and can rarely be hereditary. Most are asymptomatic and are therefore often an incidental finding. 15 At US, it has a very aspecific and heterogeneous appearance, and can even mimic a cyst. In CT they show as solid homogeneous mass, where calcification may be present, which enhances less than the renal cortex (clear cell carcinoma instead has a very high enhancement). They show progressive enhancement in excretory phase In MR they are hypointense both on T1W and T2W images and may reveal a hypointense pseudo-capsule. Specific sequences, like subtract perfusion images, can be helpful in the differentiation. Cysts and Complex cystic masses Often cysts do not require any treatment but other times they may need follow up and even surgery. In order to differentiate between these different approaches we use the Bosniak classification. The Bosniak classification was described in 1986. This classification helps the radiologist to categorize each cystic renal mass as "nonsurgical" (eg. benign in category 1 and 2) or as "surgical" (eg. requiring surgery in category 3 and 4), with a 2F being an intermediate situation, requiring follow-up. After the original description, it became obvious that there were some category II cysts that were slightly more complicated than most category II lesions, but not complicated enough to place them in category III. For that reason, a category IIF (F for follow-up) was introduced in 1993. Category 1: simple cysts, you may or may not see a wall because it is very small and hyperechoic, they are rounded and totally benign so they can just be ignored. Category 2: can have very thin calcifications inside; mildly complicated benign cysts, they can have some interior very small septa. No enhancement of septa or wall. Still benign. Category 2F ('F' for follow-up): moderately complicated cystic masses, mostly benign but require follow-up imaging to demonstrate stability and therefore benignity. They are more complex: have more than one septa, bigger than 1 mm. It can have a light enhancement in the post-contrast acquisition if we do a CT or MR in this patient. In this case the patients needs a follow-up, because this cyst has a 5-6% of malignancy (even if it is low, we have to be sure that it doesn’t change by doing follow up) Category 3: indeterminate masses that require surgery in most cases can be difficult to differentiate and are subject to variability. They have thick, multiple septations, septal nodularity and are hyperdense on CT with calcifications. Treated with a partial nephrectomy or radiofrequency ablation. Category 4: clearly malignant mass (100% malignant), tipically mixed, with a cystic part and a mass portion. In patients with polycystitis in the kidneys it can be tricky to assess the lesions. 16 Take home message It is crucial to distinguish between surgical or non surgical mass (in the first case the patient goes to the urology department, in the second they go home and just undergo follow-ups). For differentiation of renal masses first determine whether a lesion is a cyst. If it is, we can classify it according to the Bosniak classification. If it is not, look for macroscopic fat (hypoechoic) to diagnose AML. Otherwise exclude tumor-mimics like abscess or infarction (even though you would have different symptoms). Then exclude metastatic disease and lymphoma. Eventually a final answer may be given by CT and MRI. A 2nd level imaging exam is always needed. To distinguish between different masses, be aware of the specific characteristics of each of them specifically. Be aware of pseudomasses: pyelonephritis and renal abscess can be tumor mimics, but in most cases the history of the patient and the clinical findings help you to make the right diagnosis. Renal abscess is usually a complication of acute pyelonephritis and patients present with urinary tract infection, flank pain and fever. 17 The professor skipped some slides. For the sake of completeness, these are those slides: 18 19