GU Imaging

·         IVU:

1. All urinary stones are dense on CT scans, including those that are radiolucent (and therefore undetectable) on plain radiographs.
2. A renal mass detected on an IVU should be further characterized by cross-sectional imaging.
3. Patients with suspected acute renal colic are best evaluated with noncontrast CT rather than an IVU.

·         A retrograde pyelogram is performed if the patient cannot receive IV contrast because of renal insufficiency or a history of severe contrast allergy. Retrograde examination can also be performed if the IVU fails to show the entire pyelocalyceal system or ureter or to further evaluate an abnormality seen on an IVU.

·         The posterior urethra has smooth muscle that relaxes when the detrusor muscle contracts during voiding and is thus best seen on a VCUG. Although visualized on a VCUG, the anterior urethra is better evaluated by a RUG, which is performed by placing a Foley catheter in the tip of the penis and injecting contrast under fluoroscopic guidance.

·         In patients who have undergone cystectomy (usually performed for muscle-invasive bladder cancer), the ureters are connected to a loop of ileum known as an ileal conduit. The ileal conduit is excluded from the intestinal stream and is connected to the anterior abdominal wall through a stoma; a urinary drainage bag is usually applied to the stoma site. A loopogram is performed to evaluate the conduit and the upper urinary tracts. A catheter is placed in the ileal conduit, and contrast is injected under fluoroscopic guidance until it refluxes in a retrograde fashion into the ureters and the pyelocalyceal systems.

·         MRI and ultrasound are excellent at demonstrating the uterus, but both studies are poor at showing the normal fallopian tubes. Dilated fallopian tubes (hydrosalpinx) can be identified on MRI and ultrasound, but abnormality in nondilated tubes is best seen on a hysterosalpingogram.

·         Bosniak system for cystic renal lesions

·         Persons with ADPCKD often also develop multiple liver cysts and are at increased risk for developing intracerebral aneurysms. There is no increased risk of RCC.

·         Von Hippel-Lindau syndrome and the very rare hereditary papillary RCC syndrome are both autosomal dominantly inherited and associated with the development of multiple RCCs. A diagnosis of one of these syndromes often leads to screening of first-degree relatives because they may also carry the disease gene.

·         CT AND MRI OF THE KIDNEY

1.       An enhancing renal mass that does not contain macroscopic fat is an RCC until proven otherwise.

2.       An enhancing renal lesion with macroscopic fat is a benign angiomyolipoma.

3.       Cystic renal lesions that contain thick internal septations, thick mural calcification, or enhancing mural nodules are suggestive of cystic RCCs and should be excised.

·         Oncocytomas are solid, enhancing lesions that may display a central, hypoenhancing scar and tend to be relatively homogeneous for lesion size. Because these findings can also be seen in RCC, oncocytomas cannot be reliably differentiated from RCCs on CT or MRI. Although most exhibit benign behavior, there have been reports of rare metastases from oncocytomas. They are perhaps best thought of as lesions of low malignant potential, and most can be excised with partial nephrectomy.

·         Multilocular cystic nephroma: This unusual lesion is found in young boys and in older women. As its name suggests, it appears as an agglomeration of multiple cystic spaces. In approximately one third of cases, the lesion can herniate into the renal collecting system.

·         Intravenous urography (IVU) remains superior to CT and MRI for detecting TCC, although multidetector CT urography and gadolinium-enhanced MR urography are rapidly gaining acceptance as viable alternatives to IVU in imaging patients for suspected TCC.

TCC is hyperintense on T1-weighted images and hypointense on T2-weighted images compared with surrounding urine.

·         PTLD is a spectrum of diseases ranging from benign lymphoid proliferation to malignant lymphoma. PTLD is caused by the Epstein-Barr virus and is seen in transplant patients receiving immunosuppressive medications such as azathioprine (Imuran), muromonab-CD3 (Orthoclone OKT3), and cyclosporine. Greater amounts of immune suppression are associated with higher rates of incidence of PTLD. Liver transplant recipients are at greater risk for PTLD than are renal transplant recipients.

·         Horseshoe kidney is more common in patients with Turner's syndrome.

·         Chemical shift imaging is an MRI technique that is used to determine whether both lipid and water protons are present with the same small voxel (three-dimensional pixel) of space. T1-weighted gradient-echo images are obtained both "in phase" (meaning that the signals of lipid and water protons are additive and both contribute to the observed signal intensity) and "out of phase" (meaning that the signals of lipid and water protons are destructive to one another; if both are present in a voxel, their signals will tend to cancel each other out). If one therefore compares an in-phase image with an out-of-phase image, there will be less signal on the out-of-phase image in areas that contain both lipid and water protons.

·         The presence of intracytoplasmic lipid is very specific for the diagnosis of benign adenoma. About 70% of all adrenal adenomas exhibit the presence of this lipid and are termed "lipid-rich" adenomas. The remainder are termed "lipid-poor" adenomas.

MRI is very sensitive at detecting intracytoplasmic lipid. T1-weighted gradient-echo images can be obtained both in-phase and out-of-phase. If the signal intensity within the adrenal lesion on the out-of-phase image is 20% less than the signal within the lesion on the in-phase image, this demonstrates that there is intracytoplasmic lipid present, and the lesion is therefore a benign adenoma

·         If unenhanced CT does not characterize the adrenal lesion, IV contrast can be given. CT imaging of the adrenal gland is performed both 80 seconds and 10 minutes after contrast administration. Region-of-interest measurements are taken of the adrenal lesion on both the 80-second and 10-minute scan, and a percentage of "washout" is calculated. The percentage of contrast agent washout is equal to [1 - (attenuation at 10 minutes/attenuation at 80 seconds)] × 100%.

Washout that is greater than 50% is very specific for benign adrenal adenoma. Metastatic disease characteristically displays washout of less than 50%. Interestingly, the presence or absence of intracytoplasmic lipid within an adenoma does not make a lesion more or less likely to display washout.

·         A collision tumor is a metastasis to an adrenal gland that also contains an adrenal cortical adenoma. Fortunately, these are not common; however, it is worth remembering that in patients with known malignancies, one should be careful about calling a lesion an adenoma if the lesion contains two distinct parts that display very different CT and MRI characteristics.

·         Adrenal cysts and pheochromocytoma can both be markedly hyperintense on T2, although many pheochromocytomas will contain regions that are not T2-hyperintense. These two lesions are easily differentiated by administration of IV gadolinium chelate. Cysts do not enhance, and pheochromocytomas enhance avidly on both CT and MRI.

·         MEN I (Wermer's syndrome) is characterized by parathyroid hyperplasia, pituitary tumors, and pancreatic islet cell tumors.

MEN IIa (Sipple's syndrome) is characterized by pheochromocytoma, medullary thyroid carcinoma, and hyperparathyroidism.

MEN IIb is similar to MEN IIa but without parathyroid involvement and with the presence of multiple mucosal neuromas and ganglioneuromas throughout the gastrointestinal tract.

·         Cysts within the cervix are called Nabothian cysts. They represent dilated or obstructed endocervical glands. They are very common in women of reproductive ages and are usually of no clinical significance. Occasionally, the cysts appear complicated, secondary to hemorrhage or infection. Nabothian cysts can be a cause of benign cervical enlargement if they are large or multiple.

Bartholin cysts arise from obstruction of the Bartholin glands, which are located in the distal (inferior) posterolateral vagina. Gartner duct cysts are congenital lesions located in the anterolateral aspect of the proximal (superior) vagina. Both of these lesions show the typical high T2-weighted signal of cysts. The T1-weighted signal may vary if they are complicated with infection or proteinaceous content.

·         The diagnosis of mature teratoma is made by identifying macroscopic fat within an ovarian lesion. Fat within an ovarian lesion can be conclusively identified by performing the same T1-weighted sequence, both with and without explicit fat saturation. Macroscopic fat will follow the signal intensity of the body wall fat on all pulse sequences. It will be very bright on T1-weighted images performed without fat saturation and dark on the T1-weighted images performed with fat saturation.

·         The septate uterus and bicornuate uterus are the most common abnormalities and are also the most common types to result in infertility. The septate uterus causes spontaneous abortion more commonly than the bicornuate uterus. The treatment for these two abnormalities also differs. The septate uterus can be treated with hysteroscopic resection of the septum. The bicornuate uterus is treated with open surgery.

MRI can generally distinguish between these two abnormalities. A septate uterus will have a smooth outer contour and a fibrous septum. A bicornuate uterus will display a depression (1 cm or greater) of the outer contour of the fundus; and a thicker, more muscular septum.

·         PROSTATE CANCER

1. Prostate cancer usually occurs in the peripheral zone.
2. Bone metastases are very unlikely with a PSA of <10.
3. Extracapsular extension indicates nonsurgical disease. Patients are treated with chemotherapy or hormonal therapy.
4. Prostate cancer (hypointense) may be distinguished from postbiopsy hemorrhage (hyperintense) on T1 sequences. Both are generally hypointense on T2.

·         Testicular microlithiasis can be seen on ultrasound but generally is not demonstrated on MRI. It refers to minute calcifications (>5 foci per cross-sectional image) associated with cryptorchidism, Klinefelter's syndrome, and pseudohermaphrodism. Although not a premalignant condition, it may be a marker of increased risk for testicular cancer. Yearly ultrasound examinations are recommended at some institutions to screen for tumor.

·         TESTICULAR CANCER

1.       Testicular cancer is the most common soild neoplasm in men 20-40 years old.

2.       Germ cell tumors are most the common tumor type overall.

3.       The most common testicular neoplasm is seminoma in young men and lymphoma in the elderly.

4.       Seminoma has the best prognosis of germ cell tumors and is radiosensitive.

5.       Lymphatic spread of testicular cancer is first to retroperitoneal lymph nodes, unless there is invasion of the scrotal skin or prior surgery, in which case pelvic nodes may be involved early.

·         TESTICULAR TORSION

1. A testicular torsion is usually due to the bell clapper deformity in teenagers.
2. The diagnosis of a testicular torsion is based on the identification of abnormal blood flow, not the gray scale appearance
3. A normal gray scale appearance (<6 hours) suggests viability.
4. Venous flow becomes abnormal before arterial flow.
5. False-negative results may be due to detorsion or partial torsion.
6. A testicle may be hyperemic after detorsion, simulating orchitis.

·         Cowper's duct syringocele: It is cystic dilation of the main duct of the bulbourethral glands. It appears as a T2-hyperintense midline structure ventral to the proximal bulbous urethra (in the expected region of the Cowper's ducts). It may present with vague clinical symptoms, including postvoid dribbling, weak stream, frequency, and hematuria.