Figure 2.
A, Ten-year old African-American
male with sickle-cell trait. Coronal CT scan shows a centrally located and
infiltrating left renal mass. Nephrectomy was performed and surgical pathology
came back as renal medullary carcinoma. B, Large right renal mass in a 7-month old male.
Nephrectomy was performed and the surgical pathology revealed a rhabdoid tumor. C, Two -year old male with a large left renal mass
indistinguishable from a Wilms tumor. The mass was a clear cell sarcoma on
surgical pathology. D, Four-year old female with history of
abdominal enlargement. The kidneys are enlarged and show multiple
hypodensities. There are also enlarged retroperitoneal lymph nodes (arrow); E, Follow-up CT 5 months later after
chemotherapy showing normal kidneys and resolution of the retoperitoneal
lymphadenopathy.
Malignant Rhabdoid Tumor (MRT)
MRT is a rare, aggressive malignancy
that most commonly originates in the kidney (Figure 2B) but can also occur in the central nervous system and
other extrarenal sites. It is commonly
diagnosed between 0-3 years of age. It
is also associated with extensive metastasis at the time of diagnosis and can
have a synchronous brain tumor. A key to the diagnosis is negativity of
immunohistochemistry for SWI/SNF-related, matrix-associated, actin-dependent
regulator of chromatin, sub-family B, member 1 INI1 (SMARCB1) (17). There is no
standard treatment for MRT and prognosis is very poor with published overall
survivals of 15-36%, however more recent treatment regimens including surgery,
radiotherapy, high dose chemotherapy and autologous stem cell rescue
(HDCT/ASCR) may improve survival with one center reporting overall survival of
66.7% with a median follow up of almost 2 years (18).
Clear cell sarcoma of the kidney (CCSK)
CCSK is the second most common renal
tumor in children with a mean age of diagnosis overlapping with Wilms
tumor. Clinical presentation includes
abdominal pain, hypertension, and hematuria.
CCSK is aggressive with a unique propensity to metastasize to bone and
brain, as well as lung and abdomen (19).
It is virtually indistinguishable from Wilms tumor on imaging (Figure 2C). Treatment consists of radical nephrectomy,
chemotherapy, and radiotherapy. While
prognosis traditionally has been poor, newer treatment regimens show
relapse-free and cancer-specific survival rate of 100% for revised stage 1 CCSK
(20) and overall survival rate for patients with CCSK of 83% (21).
Lymphoma
Primary lymphoma of the kidney is
extremely rare since the kidney has no lymphatic system. Disease involvement is
mainly due to hematogenous or direct spread from adjacent lymph nodes. The kidneys are involved in 12% of children
with non-Hodgkin’s lymphoma. On imaging,
lymphoma may have a variety of appearances that include multiple bilateral
low-attenuation masses (Figure 2D, E),
areas of geographic wedge shaped low attenuation, unilateral solitary
low-attenuation mass, unilateral large conglomerate masses, or unilateral
nephromegaly seen on CT (22). Lymphoma
may mimic nephroblastomatosis, however, lymphoma occurs typically in older
children and is associated with lymphadenopathy elsewhere in the body.
Treatment is mainly with chemotherapy;
however careful nephrological monitoring is necessary during treatment since
excretion of tumor metabolites may result in renal obstructive or uric acid nephropathy
(23).
Conclusion
Although Wilms tumor is the most common
pediatric renal malignancy, it is often indistinguishable from other rare but
more aggressive masses like RCC and MRT. Imaging and histologic
characterization are crucial to avoid delay in management. New treatment regimens continue to improve
survival rates, however further research and advancement in knowledge is still
necessary to improve outcomes and decrease treatment-related long-term
complications.
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