Renal medullary carcinoma is a very rare and highly aggressive variant of renal cell carcinoma centered in the renal medulla.
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Epidemiology
The overwhelming majority of cases occur in individuals with sickle cell trait (HbAS) and, less commonly, with the hemoglobin SC (HbSC) variant of sickle cell disease. This prompted the authors who first defined it to name it the "seventh sickle cell nephropathy" 2. As such, a central renal mass in a young (<50 years) patient with sickle cell trait should alert one to the possibility of renal medullary carcinoma. It affects adolescents and young adults and is more common in males, especially among adolescent patients. Mean age at presentation is around 20 years, with a range of 11-39 years.
Clinical presentation
Presenting symptoms include frank hematuria, abdominal or flank pain, a palpable mass, and possibly, signs of metastatic disease. The latter are due to the fact that at the time of diagnosis, most patients will have developed metastatic disease. Similarly to other types of renal cancer, the lungs are the most common location for distant metastases and virtually every patient with liver metastases has lung metastases.
Pathology
Renal medullary carcinoma is of epithelial origin and is thought to arise from renal papillae or calyceal epithelium 4. They tend to hemorrhage and develop necrosis. They also tend to involve vascular and lymphatic structures early on.
Microscopically, these tumors are composed of sheets of poorly differentiated cells commonly found to have a reticular growth pattern and adenoid cystic component with an infiltrate of neutrophils. Sickled erythrocytes in the specimen are pathognomonic.
It exhibits SMARCB1/INI1 loss at immunohistochemistry, found in several other types of childhood malignancies, such as malignant rhabdoid tumor of the kidney and atypical teratoid/rhabdoid tumor (AT/RT) 6.
Radiographic features
Renal medullary carcinoma is a centrally located solid mass with a predilection for the right kidney. It usually has infiltrative borders and in a minority of cases, sharp borders. Mean maximum length is ~6.5 cm. Caliectasis is virtually always present. Peripheral satellite nodules and extension into renal sinus fat and perirenal extension are commonly present 5-7.
Vascular involvement can be seen, e.g. renal vein tumor thrombus.
Enlarged retroperitoneal lymph nodes are present in a great majority of cases.
The most common pattern of lung metastasis is lymphangitic carcinomatosis. Virtually all of the patients who exhibit this pattern also have mediastinal lymphadenopathy. Other patterns are lung nodules with hazy borders, nodules with sharp borders, and cannonball metastases 5,6.
Hepatic metastases are hypodense.
Tumor features on ultrasonography have not been described extensively.
CT
Renal medullary carcinoma usually appears as a central infiltrative mass. It is hypoenhancing compared to renal parenchyma, as it is a hypovascular lesion. Hemorrhage, both intratumoral and subcapsular, and necrosis are common. Calcification is uncommon.
MRI
Hemorrhage and liver metastases are both better depicted at MRI compared with CT 5.
Treatment and prognosis
There is no recommended treatment. Treatment protocols used in other types of renal carcinoma have all been tried but response to any treatment is very poor. The accepted treatment for patients without metastatic disease is total or radical nephrectomy. Patients with metastases at presentation undergo chemotherapy and/or radiotherapy but again, response to either is poor. Overall prognosis is dismal: depending on the cohort the publication is based on, mean survival time is between 4 and 12 months; a good estimate is 7.7 months 3.
Differential diagnosis
The differential diagnosis of renal medullary carcinoma includes:
-
renal cell carcinoma (RCC): extremely rare in children without von Hippel-Lindau syndrome
- collecting duct carcinoma subtype of RCC shares many features with renal medullary carcinoma: both favor the right kidney, are centrally located, and are aggressive
- rhabdoid tumor: age 3 years or younger
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