Renal cyst | |
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Other names | Kidney cysst |
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Renal cyst of the left kidney (hyperintense area) as shown on MRI. | |
Specialty | Urology ![]() |
A renal cyst is a fluid collection in or on the kidney. There are several types based on the Bosniak classification. The majority are benign, simple cysts that can be monitored and not intervened upon. However, some are cancerous or are suspicious for cancer and are commonly removed in a surgical procedure called nephrectomy.
Numerous renal cysts are seen in the cystic kidney diseases, which include polycystic kidney disease and medullary sponge kidney.
Renal cysts are classified by malignant risk using the Bosniak classification system. The system was created by Morton Bosniak (1929–2016), a faculty member at the New York University Langone Medical Center in New York City. [1]
The Bosniak classification categorizes renal cysts into five groups. [2]
This category includes renal cysts with multiple thin septa, a septum thicker than hairline, slightly thick wall, or with calcification, which may be thick. It also includes intrarenal cysts larger than 3 centimetres (1.2 inches) if:
Category IIF cysts have a 5–10% risk of being kidney cancer, and therefore follow-up is recommended. However, there is no consensus recommendation on the appropriate interval of follow up. [7]
The presence of measurable contrast enhancement of the lesion is the most important characteristic in distinguishing between high-risk cysts (classifications III and IV) from the typically benign, low-risk Bosniak I, II, and IIF cysts. [8] Such contrast enhancement should be at least 10 to 15 Hounsfield units higher when compared with unenhanced images.
Bosniak category | |||||
---|---|---|---|---|---|
I | II | IIF | III | IV | |
Attenuation [3] | 0–20 HU | 60–70 Hounsfield units | |||
Walls [3] | Thin and smooth | Small and fine calcifications | Nodular or irregular calcifications | Thick, heterogeneous. Gross calcifications with enhancement | |
Solid components [3] | No | Yes | |||
The complex cyst can be further evaluated with doppler ultrasonography, and for Bosniak classification and follow-up of complex cysts, either contrast-enhanced ultrasound (CEUS) or contrast CT is used. [12]
This system is more directly focused on the most appropriate management. These alternatives are broadly to ignore the cyst, schedule follow-up or perform a surgical excision of it. When a cyst shows discrepancy in severity across categories, it is the most worrisome feature that is used in deciding about management. There is no established rule regarding the follow-up frequency, but one possibility is after 6 months, which can later be doubled if unchanged. [5]
Recommended management [5] | |||
---|---|---|---|
Ignore | Follow | Excise | |
Calcification |
| Thick, nodular | |
If radiodensity > 20 HU without radiocontrast |
|
|
|
Septations | Thin and smooth | Slightly greater than hairline |
|
Enhancement (increase with radiocontrast) | < 10 HU | 10–15 HU | > 15 HU |
Multilocular | If infection | All others | |
Nodularity [5] | Very small and nonenhancing | All others | |
Wall thickening [5] | If infection | All others | |
Parapelvic cysts originate from around the kidney at the adjacent renal parenchyma, and plunge into the renal sinus. Peripelvic cysts are contained entirely within the renal sinus, possibly related to dilated lymphatic channels. When viewed on CT in absence of contrast, they can mimic hydronephrosis. [14] If symptomatic, they can be laparoscopically decorticated - removal of the outer layer or cortex. [15]
Up to 27 percent of individuals older than 50 years may have simple renal cysts that cause no symptoms. [16]
Medical ultrasound includes diagnostic techniques using ultrasound, as well as therapeutic applications of ultrasound. In diagnosis, it is used to create an image of internal body structures such as tendons, muscles, joints, blood vessels, and internal organs, to measure some characteristics or to generate an informative audible sound. The usage of ultrasound to produce visual images for medicine is called medical ultrasonography or simply sonography, or echography. The practice of examining pregnant women using ultrasound is called obstetric ultrasonography, and was an early development of clinical ultrasonography. The machine used is called an ultrasound machine, a sonograph or an echograph. The visual image formed using this technique is called an ultrasonogram, a sonogram or an echogram.
A cyst, also traditionally known from Old English as a wen, is a closed sac, having a distinct envelope and division compared with the nearby tissue. Hence, it is a cluster of cells that have grouped together to form a sac ; however, the distinguishing aspect of a cyst is that the cells forming the "shell" of such a sac are distinctly abnormal when compared with all surrounding cells for that given location. A cyst may contain air, fluids, or semi-solid material. A collection of pus is called an abscess, not a cyst. Once formed, a cyst may resolve on its own. When a cyst fails to resolve, it may need to be removed surgically, but that would depend upon its type and location.
Liver tumors are abnormal growth of liver cells on or in the liver. Several distinct types of tumors can develop in the liver because the liver is made up of various cell types. Liver tumors can be classified as benign (non-cancerous) or malignant (cancerous) growths. They may be discovered on medical imaging, and the diagnosis is often confirmed with liver biopsy. Signs and symptoms of liver masses vary from being asymptomatic to patients presenting with an abdominal mass, hepatomegaly, abdominal pain, jaundice, or some other liver dysfunction. Treatment varies and is highly specific to the type of liver tumor.
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Thyroid nodules are nodules which commonly arise within an otherwise normal thyroid gland. They may be hyperplastic or tumorous, but only a small percentage of thyroid tumors are malignant. Small, asymptomatic nodules are common, and often go unnoticed. Nodules that grow larger or produce symptoms may eventually need medical care. A goitre may have one nodule – uninodular, multiple nodules – multinodular, or be diffuse.
A lung nodule or pulmonary nodule is a relatively small focal density in the lung. A solitary pulmonary nodule (SPN) or coin lesion, is a mass in the lung smaller than three centimeters in diameter. A pulmonary micronodule has a diameter of less than three millimetres. There may also be multiple nodules.
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Scrotalultrasound is a medical ultrasound examination of the scrotum. It is used in the evaluation of testicular pain, and can help identify solid masses.
Renal ultrasonography is the examination of one or both kidneys using medical ultrasound.
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Emilio Quaia is an Italian radiologist, academic, and author. He is a professor of Radiology and the Director of the Radiology Department at the University of Padova.
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