Newer, less invasive imaging modalities, have led to an increased use of this technology to aid in diagnosis. Advantages of ultrasound include the fact that risks of IV contrast and x-radiation are avoided. With increased use comes increased detection. Increased use of renal ultrasound to aid in diagnosis and treatment of renal stone disease and or hydronephrosis has lead to an increased detection of asymptomatic cystic lesions of the kidneys. This newsletter focuses on the approach to cystic renal lesions.
Basic knowledge
Simple cysts are detectable in 25 to 30% of patients above the age
of 50. The majority of renal cystic lesions are in fact simple cysts.
Isolated simple cysts are benign by nature and need no further evaluation.
Still, the number of patients with more complex lesions is significant,
and some of these lesions will turn out to be renal cell carcinoma
(RCC). Over 30,000 new cases of renal cell carcinoma are diagnosed
each year and the life time risk of RCC for a 40 year old male is
1.3% (Ries et al, NIH p223, 1997). However, stage migration for
RCC is apparent and the percentage of patients presenting with advanced
disease is dropping.
What are the criteria
for a simple cyst?
Simple cysts are reliably identified by ultrasound. Characteristics
of a simple cyst include
- Anechoic character of the cyst;
- Increased through transmission with posterior enhancement;
- a sharply demarcated cyst wall.
What if the lesion
does not fill the criteria for a simple cyst?
Currently the standard for further evaluation is abdominal
CT with and without contrast. Bosniak (NYU) proposed a classification
of renal cystic lesions based on abdominal CT findings.
Bosniak I—Thin
wall, no septations, no calcifications, density 0-20, No enhancement.
Bosniak II—Same but with, few septations, and or few
calcifications.
Bosniak III—Thick wall, septations, calcifications,
density 0-20, No enhancement.
Bosniak IV—Thick wall, thick septations, course calcifications,
density more than 20, enhancement.
The classification translates roughly to the following:
- We know it's a cyst
- We're still pretty certain it's a cyst
- We don't know what it is.
- It's probably a tumor
More confidence can be achieved by requesting CT intervals of 5 mm rather than the standard 10mm.
Role of MRI
In most circumstances it offers no advantage over CT. Exceptions
include: patients who have IV contrast allergy, or renal insufficiency.
Role of Aspiration
Aspiration should be avoided as a means of diagnosis in most
cases. The dilemma with aspiration occurs as follows: If the
aspiration is positive for malignancy, it is a true positive,
but there is a small risk of seeding the needle tract with tumor.
If the results are negative, the presence of malignancy is still
possible. Aspiration may be appropriate in cases of differentiation
of RCC from other tumors such a s lymphoma or a suspected metastasis
to the kidney, or finally if there is suspicion of abscess.
More renal cystic lesions are being identified. Management of simple cyst, fulfilling Bosniak I criteria requires no further evaluation. Bosniak II lesions should be monitored. Bosniak III and IV lesions are indications for surgical exploration. If lesions are small and confined to one pole of the kidney, a partial nephrectomy may be feasible.