Abstract

Simple renal cysts are the most common renal masses but the major concern is to differentiate a simple renal cyst from a complex cyst which may have foci of malignancy. However, this association is seen in 1% cases only. Most of the renal cysts are benign, asymptomatic and are usually treated conservatively. However, various cystic diseases are associated with renal cell carcinoma. Renal cysts with thickened, irregular septa and enhancement on contrast injection raise a suspicion of malignancy. We present a case of a 41 year old male who presented with renal cell carcinoma of left kidney with multiple simple renal cysts.

Keywords: Multifocal RCC, Nephrectomy, Renal cyst, Renal cell carcinoma.

Fig-4: A- Photomicrograph showing tubular arrangement of tumor cells (Green arrow) along with adjacent simple cyst (Blue arrow). (H&Ex100). B- Photomicrograph showing simple cyst of kidney lined by cuboidal epithelium and filled with proteinaceous material. (H & Ex100)

Discussion

Simple renal cyst is the most common pathology associated with urinary tract system. However, Renal Cell Carcinoma is seen to be associated with multiple simple renal cysts in only 1% cases.^[3]Case reports of this association are very rare. In the year 1875, association

between Renal Cell Carcinoma (RCC) and simple renal cysts was first proposed by Sturm.^[4]

Mostly the simple renal cysts are unilocular and benign whereas the complex cysts have thickened irregular septa & may be multiloculated. Recent advances in radiology have improved the clinical approach towards diagnosing the asymptomatic renal masses. Bosniak classification system clinically classifies the renal cystic tumors into 3 categories based on the CT findings. In category I, the incidence of malignancy is very low whereas in categories II and III, a certain risk of malignant cystic disease is included and appropriate treatment may be required.^[5],^[6]However, it may be difficult to determine preoperatively whether or not a cyst is malignant due to the small size of the malignant tissue inside the cyst, which cannot be detected by imaging alone.

Lin et al, reported a case which was initially diagnosed as a simple cyst and was treated by ultrasound?guided aspiration, but 3 weeks later ultrasound examination revealed a recur­rent sizeable cyst which was treated by performing nephrectomy. The pathological examination confirmed the diagnosis of papillary RCC.^[7] Visapaa et al, evaluated 482 patients and demon­strated an association between simple renal cysts and papillary RCC.^[8] Sakai et al, reported a case of a simple renal cyst that developed into a septated renal cyst and finally transformed into a cystic clear cell RCC over a duration of 6 years.^[9]This case demonstrated the natural transformation of a simple renal cyst into malignancy and emphasized that careful follow?up of renal cysts, particularly of complicated type, is mandatory. Takao et al, also reported a similar case where cystic RCC was diagnosed as a simple cyst preoperatively.^[10]

Both acquired and syndromic renal cysts may be associated with Renal Cell Carcinomas such as Adult Polycystic Kidney Disease (APCKD), Von-Hippel Lindau (VHL) disease and tuberous sclerosis complex (TSC). A study conducted by Keith et al found that in association with Autosomal Dominant Polycystic Kidney Disease, Renal Cell Carcinoma develops at a younger age (47 years) as compared to sporadic Renal Cell Carcinoma (61 years). Also, it is more often bilateral (12 versus 2 to 6%) and multicentric (30 versus 5%).^[11]Breysem L et al, observed that in Tuberosus Sclerosis Complex cases, renal involvement occurs in 50 to 80% cases in the form of rnalignant cysts and renal neoplasms.^[12]

Shehata BM et al, observed that in Von-Hippel Lindau patients, renal involvement occurs in the form of multiple, bilateral clear cell-lined cysts in 70 to 80% cases and multiple, bilateral clear cell type Renal Cell Carcinoma in 40-60% cases.^[13],^[14]Association between Renal Cell Carcinoma and End Stage Kidney Disease with Autosomal Dominant Polycystic Kidney Disease was first proposed by Dunhill et al.^[15] In End Stage Kidney Disease and Autosomal Dominant Polycystic Kidney Disease patients the risk of developing Renal Cell Carcinoma increases with the duration of dialysis. The neoplasms developing in End Stage Kidney Disease and Autosomal Dominant Polycystic Kidney Disease are more often multifocal, bilateral and have a papillary appearance.^[16],^[17]Renal Cell Carcinoma associated with End Stage Kidney Disease has now been recognized as a distinct entity by World Health Organization (WHO). Also risk of RCC in acquired renal cystic disease is five times greater than in the general population. The morphology of the cysts and associated tumor types can help to predict the acquired or genetic basis of the lesions. Thus, it is important to mention these associations in the histopathology reports.^[18]

Understanding of the initiating molecular events in cyst formation & renal neoplasm in cystic diseases like Adult Polycystic Kidney Disease (APCKD), acquired cystic diseases, Von-Hippel Lindau (VHL) disease and tuberous sclerosis complex (TSC) is important as it has shown promise for developing targeted therapies for neoplasms which were previously being treated by surgical approach.

Conclusion

The aim of the present study was to emphasize the importance of recognizing that RCC may occur in what appears to be a simple renal cyst. Although, this association of RCC with simple renal cysts is seen in only one percent of cases, if the presence of malignancy is pathologically confirmed, an immediate partial or radical nephrectomy needs to be performed.

Conflicts of Interest: None.