Urol Radiol 13:94-97 (1991)
Urologic Radiology (~) Springer-Vedag New York Inc. 1991
Clinical and Imaging Features of Rhabdoid Tumor of the Kidney S. Z a f a r H . Jafri,~ J u d y L. F r e e m a n , l B a r b a r a F. R o s e n b e r g , 2 A l e x a n d e r Cacciarelli,1 a n d B e a t r i c e L. M a d r a z o ~ Departments of 1Diagnostic Radiology and 2 Pathology, William Beaumont Hospital, Royal Oak, Michigan, USA
A b s t r a c t . R h a b d o i d t u m o r o f t h e k i d n e y ( R T K ) is a rare, h i g h l y m a l i g n a n t n e o p l a s m o f c h i l d h o o d . T h e c l i n i c a l p r o f i l e o f t h i s n e o p l a s m differs f r o m t h a t o f Wilms' tumor. We present two cases of RTK. In b o t h o u r cases, large b u l k y m a s s e s w i t h p o o r l y d e fined margins and calcifications were demonstrated. The clinical and imaging findings are compared with other childhood renal neoplasms.
Key words
Kidney -- Rhabdoid tumor -- Clinical features -- Computed tomography -- Sonography.
R h a b d o i d t u m o r o f t h e k i d n e y ( R T K ) is a rare, h i g h ly m a l i g n a n t n e o p l a s m o f c h i l d h o o d . O n c e c o n s i d e r e d a v a r i a n t o f W i l m s ' t u m o r , it is n o w r e c o g n i z e d a s a s e p a r a t e n e o p l a s t i c e n t i t y w h i c h is c l i n i c a l l y a n d h i s t o l o g i c a l l y d i s t i n c t f r o m W i l m s ' t u m o r [ 1]. T h e h i s t o p a t h o l o g i c f i n d i n g s o f R T K h a v e b e e n well d e s c r i b e d in t h e l i t e r a t u r e [1]. H o w e v e r , t h e r e h a v e b e e n o n l y five c a s e s t o o u r k n o w l e d g e i n w h i c h t h e r a d i o g r a p h i c f i n d i n g s h a v e b e e n d e s c r i b e d [2-5]. W e review the computed tomographic (CT) and sonographic (US) findings of two additional cases which p r e s e n t e d a s large b u l k y m a s s e s a r i s i n g f r o m t h e kidney. The clinical and imaging features of RTK w i l l b e c o m p a r e d w i t h t h o s e o f o t h e r c h i l d h o o d renal tumors.
Case Reports Case 1 A 3-year-old girl presented with lethargy, anorexia, and a right upper quadrant abdominal mass. Blood pressure was 174/122 mmHg. An abdominal radiograph demonstrated a large soft tissue mass in the right abdomen and excretory urography showed a nonfunctioning right kidney. Real-time US demonstrated a large, predominantly echogenic mass arising from the right kidney. A bright echo with acoustic shadowing consistent with calcification, was seen within the mass (Fig. 1A). Echogenic material suggestive of tumor thrombus was visualized within the inferior vena eava. A contrast-enhanced CT scan of the abdomen demonstrated a low-density mass arising from the right kidney. The mass extended from the dome of the diaphragm to the iliac crest and crossed the midline to displace the abdominal aorta to the left. Extensive retroperitoneal adenopathy was responsible for much of the mass effect (Fig. 1B). The inferior vena cava could not be identified as a structure separate from the tumor mass. Prominence of the azygos vein and lower lumbar venous plexus was noted, suggesting the presence of collateral venous flow. On the third day following admission, the patient underwent exploratory laparotomy which revealed a large, extremely vascular mass caudal to the liver. The tumor was considered unresectable and multiple incisional biopsies were obtained. The tumor was composed of polygonal cells containing eosinophilic cytoplasm and the cells were arranged in a solid or trabecular pattern. The round to oval nuclei contained single prominent nucleoli. In occasional cells the nuclei were eccentric and the cytoplasm contained a more intensely eosinophilic globule. The globules were immunohistochemically positive for vimentin, and electron microscopic study revealed rounded bundles of intermediate filaments. These findings are characteristic of rhabdoid tumor. Chromosome analysis was not performed. The child was given chemotherapy consisting of actinomycin-D, vincristine, and doxorubicin. The child's condition worsened over the 6-week course of chemotherapy. At the parents' request, chemotherapy was discontinued. The child expired 21/2months after her initial presentation to the hospital.
Case 2 Address offprint requests to: S. Zafar H. Jafri, M.D., Department of Diagnostic Radiology, William Beaumont Hospital, 3601 West 13 Mile Road, Royal Oak, MI 48073, USA
A 5-month-old girl presented with lethargy and a left abdominal mass. Blood pressure was 136/60 mmHg. Serum calcium was
S.Z.H. Jafri et at.: Rhabdoid Tumor of the Kidney
Fig. 1. A Sagittal sonogram of the right upper quadrant demonstrates a hyperechoic mass (M) involving the upper pole of the right kidney. The normal lower pole is seen anteriorly (K). No definite interface separates the mass from the adjacent liver (L). Calcification was present in other portions of the mass (not ineluded). B Contrast-enhanced CT scan of the same patient demonstrates a large, low-density mass arising from the right kidney (K). The kidney is displaced anteriorly. There is extensive retroperitoneal adenopathy. The abdominal aorta (arrowhead)and superior mesenteric artery (arrow)are displaced by the tumor.
elevated at 24.3 mg/dl (normal 8.8-11.2 mg/dl). Real-time US demonstrated a large, heterogeneous mass arising from the upper pole of the left kidney. An echogenie focus suggestive of calcification was seen in the lower pole of the left kidney. In the midabdomen, there was a hypoechoic area which was displacing but not invading the inferior vena cava and this was consistent with retroperitoneal adenopathy (Fig. 2A). An unenhanced CT scan of the abdomen confirmed the presence of a large soft tissue mass arising from the left kidney. The mass contained multiple curvilinear areas of increased density suggestive of calcification or acute hemorrhage (Fig. 2B). Calcification was noted in the lower pole of the left kidney. Increased soft tissue density consistent with adenopathy was seen in the retroperitoneum. At operation, a large mass was found that occupied most of the left kidney, sparing only a small portion of the lower pole. The mass measured 7 era in greatest dimension, extending to the capsular surface and to the renal pelvis. Greater than 50% of the tumor was necrotic. Grossly abnormal lymph nodes were identified within the renal hilum and in the adjacent periaortic region. There was no tumor thrombus in the renal vein. The left kidney and its associated mass were removed. The lymph nodes could not be entirely resected. Upon microscopic examination, the tumor was composed of sheets and nests of fairly uniform polygonal cells containing granular, eosinophilic cytoplasm and large, rounded nuclei with prominent nudeoli. Tumor cells with eosinophilic globules and eccentric nuclei were present but infi~uent, and such cells stained for vimentin. Electron microscopy showed the globules to be bundles of intermediate filaments. Chromosome analysis was performed and demonstrated no chromosomal abnormalities. The patient's blood pressure and serum calcium levels nor-
95
realized following surgery. The child was initially given chemotherapy consisting of actinomycin-D, vincristine, and doxorubicin. A follow-up CT scan of the abdomen obtained 6 weeks after surgery demonstrated recurrence of the intraabdominal mass. Subsequently, the chemotherapy was changed to include carboplatinum, Ifosphamide, and etoposide (VP 16). The child's condition continued to worsen with development of tumor recurrence at the incisional site, ascites, and increasing retroperitoneal adenopathy as documented by serial CT scans and US. The child died 10 months after her initial presentation to the hospital. Autopsy was not performed.
Discussion R T K is o n e o f t h e m o s t a g g r e s s i v e s o l i d t u m o r s o f childhood. RTK was originally described by Beckw i t h a n d P a l m e r i n 1978 [6] a s " ' r h a b d o m y o s a r c o m a t o i d " v a r i a n t o f W i l m s " t u m o r b e c a u s e o f t h e res e m b l a n c e o f its cells, w h i c h p o s s e s s large n u c l e o l i and filamentous cytoplasmic inclusions, to rhabdomyoblasts. However, failure to demonstrate evidence of myoblastic differentiation and a lack of morphological or clinical linkage to Wilms' tumor, supported the view that RTK represents a separate n e o p l a s t i c e n t i t y [6]. D e s p i t e i n t e n s i v e t r e a t m e n t regimens, the mortality rate of RTK exceeds 80% [1]. F o r t u n a t e l y , i t a c c o u n t s for o n l y 2 % o f a l l m a l i g n a n t n e o p l a s m s o f c h i l d h o o d [7]. T h e c l i n i c a l p r o f i l e o f R T K differs f r o m t h a t o f Wilms' tumor. RTK tends to present at a younger age w i t h t h e m e a n b e i n g 16.8 m o n t h s , w h e r e a s i n W i l m s ' t u m o r , t h e a v e r a g e age a t t h e t i m e o f p r e s e n t a t i o n is 4.7 y e a r s [1]. R T K h a s b e e n a s s o c i a t e d with an increased incidence of primary central nervous system tumors which occurred either before, after, o r c o n c u r r e n t l y w i t h t h e r e n a l l e s i o n . T h e s e tumors occurred either in the posterior fossa or just above the tentorium cerebelli and most were diagn o s e d a s m e d u l l o b l a s t o m a . O t h e r s w e r e t h o u g h t to
96
Fig. 2. A Sagittal sonogram of the left upper quadrant demonstrates a heterogeneous mass arising from the left kidney. Bright echoes (arrows)indicate the presence of calcification. Associated adenopathy (A) is also seen. B Unenhanced CT scan of the abdomen reveals a large mass arising from the left kidney. Multiple areas of increased density indicate the presence of calcification (arrow). There is soft tissue density around the aorta consistent with adenopathy (A).
represent primitive neuroectodermal tumors, ependymomas, or gliomas o f the cerebellum or brain stem [ 1]. No increased incidence of central nervous system tumors has been reported with Wilms' tumor. Anomalies associated with Wilms' tumor, such as aniridia, hemihypertrophy, hypospadias, and cryptorchidism, are not described in patients with RTK. Nephrogenic rests, found in 25--400/0 of kidneys containing Wilms' tumor, have not been encountered in R T K [ 1]. With the advent of effective chemotherapy in the early 1960s, the overall survival rate of patients with Wilms' tumor improved and is now approximately 80% [8]. R T K is resistant to the chemotherapeutic agents which are so effective in the treatment of Wilms' tumor, thus accounting for the high mortality rate of R T K [7]. In one o f our patients (case 2), serum calcium was elevated at the time of presentation, without evidence of bone metastases. The serum calcium normalized following surgery. Leblanc et al. also described three infants with R T K who had hypercalcemia without evidence of osseous involvement. In Leblanc's series, there was complete resolution o f the hypercalcemia following surgery, suggesting that a humoral factor produced by the tumor cells was responsible for the elevated calcium levels [9]. Other neoplastic conditions with which hypercalcemia has been associated in children include neuroblastoma, leukemia, hepatoblastoma, testicular
S.Z.H. Jafri et al.: Rhabdoid Tumor of the Kidney
carcinoma, dysgerminoma, and lymphoma. Hypercalcemia is rare in patients with Wilms' tumor [ 10]. Clear cell sarcoma of the kidney was also once considered a sarcomatous variant of Wilms' tumor and is now recognized as a distinct neoplastic entity. It accounts for approximately 4% of all childhood renal tumors and has a mortality rate of approximately 50% [8]. Referred to as "bone metastasizing renal tumor of childhood" by Marsden et al., it has a reported incidence of bone metastases of 76% [ 11 ]. R T K rarely metastasizes to the skeletal system, with osseous involvement reported in less than 5% of cases [1]. Wilms' tumor also rarely metastasizes in this manner with reported incidences of osseous involvement ranging from 0.5 to 13% [12]. In both of our cases of RTK, large bulky masses with poorly defined margins and associated calcification were demonstrated by US and CT. This is in contrast to classic Wilms' tumor which commonly is seen on CT as a well-circumscribed mass with "clean" margins and a prominent pseudocapsule composed of compressed, enhanced renal tissue. Less commonly, Wilms' tumor exhibits an infiltrative growth pattern with a resultant mass that is ill-defined and poorly marginated [8]. It is apparent that the poorly defined margins of R T K are not helpful in differentiating this neoplasm from other renal tumors of childhood. It has recently been emphasized that R T K characteristically assumes a medial location within the kidney, whereas Wilms' tumor tends to arise in the outer cortex [1]. Although calcification was demonstrated on US and CT in both of our cases of RTK, this, however, could not be confirmed histologically in case 1, since only random biopsies were obtained. In the second case, calcifications were demonstrated in the portions of the kidney uninvolved by tumor. This may be secondary to the associated hypercalcemia. The exact significance of this finding is uncertain and it
97
S.Z.H. Jafri et al.: Rhabdoid Tumor of the Kidney has not been described previously with R T K . Calcification is u n c o m m o n in W i l m s ' tumor, occurring in only 3-5% o f patients. Retroperitoneal adenop a t h y was a significant finding in both o f our cases. This finding usually indicates a p o o r prognosis. Local metastasis to regional l y m p h nodes has frequently been observed in W i l m s ' tumor. In a small n u m ber o f cases o f W i l m s ' t u m o r , fat has b e e n d e m o n s t r a t e d in the renal mass on CT. T o our knowledge this has not been seen with R T K [8].
Summary In s u m m a r y , two cases o f R T K are described, both in very y o u n g children who presented with a b d o m inal masses. It is apparent from the clinical and pathological features o f R T K that this neoplasm comprises a discrete entity which should be considered in the differential diagnosis o f a large renal mass presenting in a y o u n g child. T h e radiographic features, however, do not help in distinguishing this neoplasm from other renal neoplasms o f childhood. This t u m o r has a dismal prognosis; no effective treatment has yet been devised. The high mortality rate o f R T K necessitates additional studies to further elucidate the pathobiology o f this t u m o r a n d to develop a treatment protocol which is effective in its management.
References 1. Weeks DA, Beckwith JB, Mierau GW, Luckey DW: Rhabdoid tumor of kidney. A report of 111 cases from the national Wilms' tumor study pathology center. Am J Surg Patho113: 439-458, 1989 2. MontgomeryP, Kuhn JP, BergerPE: Rhalxloid tumor of the kidney. A case report. Urol Rad 7:42-44, 1985 3. Shirkhoda A: Radiologic Oncology of the Abdomen and Pelvis, an Atlas and Text. Yearbook Medical Publishers, 1988, pp 653-750 4. Sisler CL, Siegel MJ: Malignant rhabdoid tumor of the kidney. Radiologic features. Radiology 172:211-212, 1989 5. Lowe W, Weiss RM, Todd MB, True LD: Malignant rhabdoid tumor of the kidney in an adult. J Urol 143:110-112, 1990 6. BeckwithJB, Palmer NF: Histopathologic and prognosis of Wilms' tumor. Results from the first national Wilms' tumor study. Cancer 41:1937-1948, 1978 7. Palmer NF, Sutow W: Clinical aspects of the rhabdoid tumor of the kidney: A report of the national Wilms' tumor study group. Med Pediatr Oncol 11:242-245, 1985 8. Kagan RA, Steckel 1LI:Clear cell sarcoma of the kidney: A renal tumor of childhood that metastasizes to bone. AJR 146:64-66, 1986 9. Leblanc A, Cailland JM, Hartmann O, et al.: Hypercalcemia preferentially occurs in unusual forms of childhood nonHodgkins lymphoma, rhabdomyosarcoma and Wilms' tumor. A study of 11 cases. Cancer 54:2132-2136, 1984 10. A1-RashidRA,Cress C: Hypercalcemiaassociated with neuroblastoma. Am J Dis Child 133:838-841, 1979 11. Marsden HB, Fowler W, Kumar PM: Bone metastasizing renal tumor of childhood: Morphologicand clinical features, and differences from Wilms' tumor. Cancer 42:1922-1928, 1978 12. Lamego C, Zerbini M: Bone metastasizing primary renal tumors in children. Radiology 147:449-454, 1983
Urologic Radiology (~) Springer-Vedag New York Inc. 1991
Clinical and Imaging Features of Rhabdoid Tumor of the Kidney S. Z a f a r H . Jafri,~ J u d y L. F r e e m a n , l B a r b a r a F. R o s e n b e r g , 2 A l e x a n d e r Cacciarelli,1 a n d B e a t r i c e L. M a d r a z o ~ Departments of 1Diagnostic Radiology and 2 Pathology, William Beaumont Hospital, Royal Oak, Michigan, USA
A b s t r a c t . R h a b d o i d t u m o r o f t h e k i d n e y ( R T K ) is a rare, h i g h l y m a l i g n a n t n e o p l a s m o f c h i l d h o o d . T h e c l i n i c a l p r o f i l e o f t h i s n e o p l a s m differs f r o m t h a t o f Wilms' tumor. We present two cases of RTK. In b o t h o u r cases, large b u l k y m a s s e s w i t h p o o r l y d e fined margins and calcifications were demonstrated. The clinical and imaging findings are compared with other childhood renal neoplasms.
Key words
Kidney -- Rhabdoid tumor -- Clinical features -- Computed tomography -- Sonography.
R h a b d o i d t u m o r o f t h e k i d n e y ( R T K ) is a rare, h i g h ly m a l i g n a n t n e o p l a s m o f c h i l d h o o d . O n c e c o n s i d e r e d a v a r i a n t o f W i l m s ' t u m o r , it is n o w r e c o g n i z e d a s a s e p a r a t e n e o p l a s t i c e n t i t y w h i c h is c l i n i c a l l y a n d h i s t o l o g i c a l l y d i s t i n c t f r o m W i l m s ' t u m o r [ 1]. T h e h i s t o p a t h o l o g i c f i n d i n g s o f R T K h a v e b e e n well d e s c r i b e d in t h e l i t e r a t u r e [1]. H o w e v e r , t h e r e h a v e b e e n o n l y five c a s e s t o o u r k n o w l e d g e i n w h i c h t h e r a d i o g r a p h i c f i n d i n g s h a v e b e e n d e s c r i b e d [2-5]. W e review the computed tomographic (CT) and sonographic (US) findings of two additional cases which p r e s e n t e d a s large b u l k y m a s s e s a r i s i n g f r o m t h e kidney. The clinical and imaging features of RTK w i l l b e c o m p a r e d w i t h t h o s e o f o t h e r c h i l d h o o d renal tumors.
Case Reports Case 1 A 3-year-old girl presented with lethargy, anorexia, and a right upper quadrant abdominal mass. Blood pressure was 174/122 mmHg. An abdominal radiograph demonstrated a large soft tissue mass in the right abdomen and excretory urography showed a nonfunctioning right kidney. Real-time US demonstrated a large, predominantly echogenic mass arising from the right kidney. A bright echo with acoustic shadowing consistent with calcification, was seen within the mass (Fig. 1A). Echogenic material suggestive of tumor thrombus was visualized within the inferior vena eava. A contrast-enhanced CT scan of the abdomen demonstrated a low-density mass arising from the right kidney. The mass extended from the dome of the diaphragm to the iliac crest and crossed the midline to displace the abdominal aorta to the left. Extensive retroperitoneal adenopathy was responsible for much of the mass effect (Fig. 1B). The inferior vena cava could not be identified as a structure separate from the tumor mass. Prominence of the azygos vein and lower lumbar venous plexus was noted, suggesting the presence of collateral venous flow. On the third day following admission, the patient underwent exploratory laparotomy which revealed a large, extremely vascular mass caudal to the liver. The tumor was considered unresectable and multiple incisional biopsies were obtained. The tumor was composed of polygonal cells containing eosinophilic cytoplasm and the cells were arranged in a solid or trabecular pattern. The round to oval nuclei contained single prominent nucleoli. In occasional cells the nuclei were eccentric and the cytoplasm contained a more intensely eosinophilic globule. The globules were immunohistochemically positive for vimentin, and electron microscopic study revealed rounded bundles of intermediate filaments. These findings are characteristic of rhabdoid tumor. Chromosome analysis was not performed. The child was given chemotherapy consisting of actinomycin-D, vincristine, and doxorubicin. The child's condition worsened over the 6-week course of chemotherapy. At the parents' request, chemotherapy was discontinued. The child expired 21/2months after her initial presentation to the hospital.
Case 2 Address offprint requests to: S. Zafar H. Jafri, M.D., Department of Diagnostic Radiology, William Beaumont Hospital, 3601 West 13 Mile Road, Royal Oak, MI 48073, USA
A 5-month-old girl presented with lethargy and a left abdominal mass. Blood pressure was 136/60 mmHg. Serum calcium was
S.Z.H. Jafri et at.: Rhabdoid Tumor of the Kidney
Fig. 1. A Sagittal sonogram of the right upper quadrant demonstrates a hyperechoic mass (M) involving the upper pole of the right kidney. The normal lower pole is seen anteriorly (K). No definite interface separates the mass from the adjacent liver (L). Calcification was present in other portions of the mass (not ineluded). B Contrast-enhanced CT scan of the same patient demonstrates a large, low-density mass arising from the right kidney (K). The kidney is displaced anteriorly. There is extensive retroperitoneal adenopathy. The abdominal aorta (arrowhead)and superior mesenteric artery (arrow)are displaced by the tumor.
elevated at 24.3 mg/dl (normal 8.8-11.2 mg/dl). Real-time US demonstrated a large, heterogeneous mass arising from the upper pole of the left kidney. An echogenie focus suggestive of calcification was seen in the lower pole of the left kidney. In the midabdomen, there was a hypoechoic area which was displacing but not invading the inferior vena cava and this was consistent with retroperitoneal adenopathy (Fig. 2A). An unenhanced CT scan of the abdomen confirmed the presence of a large soft tissue mass arising from the left kidney. The mass contained multiple curvilinear areas of increased density suggestive of calcification or acute hemorrhage (Fig. 2B). Calcification was noted in the lower pole of the left kidney. Increased soft tissue density consistent with adenopathy was seen in the retroperitoneum. At operation, a large mass was found that occupied most of the left kidney, sparing only a small portion of the lower pole. The mass measured 7 era in greatest dimension, extending to the capsular surface and to the renal pelvis. Greater than 50% of the tumor was necrotic. Grossly abnormal lymph nodes were identified within the renal hilum and in the adjacent periaortic region. There was no tumor thrombus in the renal vein. The left kidney and its associated mass were removed. The lymph nodes could not be entirely resected. Upon microscopic examination, the tumor was composed of sheets and nests of fairly uniform polygonal cells containing granular, eosinophilic cytoplasm and large, rounded nuclei with prominent nudeoli. Tumor cells with eosinophilic globules and eccentric nuclei were present but infi~uent, and such cells stained for vimentin. Electron microscopy showed the globules to be bundles of intermediate filaments. Chromosome analysis was performed and demonstrated no chromosomal abnormalities. The patient's blood pressure and serum calcium levels nor-
95
realized following surgery. The child was initially given chemotherapy consisting of actinomycin-D, vincristine, and doxorubicin. A follow-up CT scan of the abdomen obtained 6 weeks after surgery demonstrated recurrence of the intraabdominal mass. Subsequently, the chemotherapy was changed to include carboplatinum, Ifosphamide, and etoposide (VP 16). The child's condition continued to worsen with development of tumor recurrence at the incisional site, ascites, and increasing retroperitoneal adenopathy as documented by serial CT scans and US. The child died 10 months after her initial presentation to the hospital. Autopsy was not performed.
Discussion R T K is o n e o f t h e m o s t a g g r e s s i v e s o l i d t u m o r s o f childhood. RTK was originally described by Beckw i t h a n d P a l m e r i n 1978 [6] a s " ' r h a b d o m y o s a r c o m a t o i d " v a r i a n t o f W i l m s " t u m o r b e c a u s e o f t h e res e m b l a n c e o f its cells, w h i c h p o s s e s s large n u c l e o l i and filamentous cytoplasmic inclusions, to rhabdomyoblasts. However, failure to demonstrate evidence of myoblastic differentiation and a lack of morphological or clinical linkage to Wilms' tumor, supported the view that RTK represents a separate n e o p l a s t i c e n t i t y [6]. D e s p i t e i n t e n s i v e t r e a t m e n t regimens, the mortality rate of RTK exceeds 80% [1]. F o r t u n a t e l y , i t a c c o u n t s for o n l y 2 % o f a l l m a l i g n a n t n e o p l a s m s o f c h i l d h o o d [7]. T h e c l i n i c a l p r o f i l e o f R T K differs f r o m t h a t o f Wilms' tumor. RTK tends to present at a younger age w i t h t h e m e a n b e i n g 16.8 m o n t h s , w h e r e a s i n W i l m s ' t u m o r , t h e a v e r a g e age a t t h e t i m e o f p r e s e n t a t i o n is 4.7 y e a r s [1]. R T K h a s b e e n a s s o c i a t e d with an increased incidence of primary central nervous system tumors which occurred either before, after, o r c o n c u r r e n t l y w i t h t h e r e n a l l e s i o n . T h e s e tumors occurred either in the posterior fossa or just above the tentorium cerebelli and most were diagn o s e d a s m e d u l l o b l a s t o m a . O t h e r s w e r e t h o u g h t to
96
Fig. 2. A Sagittal sonogram of the left upper quadrant demonstrates a heterogeneous mass arising from the left kidney. Bright echoes (arrows)indicate the presence of calcification. Associated adenopathy (A) is also seen. B Unenhanced CT scan of the abdomen reveals a large mass arising from the left kidney. Multiple areas of increased density indicate the presence of calcification (arrow). There is soft tissue density around the aorta consistent with adenopathy (A).
represent primitive neuroectodermal tumors, ependymomas, or gliomas o f the cerebellum or brain stem [ 1]. No increased incidence of central nervous system tumors has been reported with Wilms' tumor. Anomalies associated with Wilms' tumor, such as aniridia, hemihypertrophy, hypospadias, and cryptorchidism, are not described in patients with RTK. Nephrogenic rests, found in 25--400/0 of kidneys containing Wilms' tumor, have not been encountered in R T K [ 1]. With the advent of effective chemotherapy in the early 1960s, the overall survival rate of patients with Wilms' tumor improved and is now approximately 80% [8]. R T K is resistant to the chemotherapeutic agents which are so effective in the treatment of Wilms' tumor, thus accounting for the high mortality rate of R T K [7]. In one o f our patients (case 2), serum calcium was elevated at the time of presentation, without evidence of bone metastases. The serum calcium normalized following surgery. Leblanc et al. also described three infants with R T K who had hypercalcemia without evidence of osseous involvement. In Leblanc's series, there was complete resolution o f the hypercalcemia following surgery, suggesting that a humoral factor produced by the tumor cells was responsible for the elevated calcium levels [9]. Other neoplastic conditions with which hypercalcemia has been associated in children include neuroblastoma, leukemia, hepatoblastoma, testicular
S.Z.H. Jafri et al.: Rhabdoid Tumor of the Kidney
carcinoma, dysgerminoma, and lymphoma. Hypercalcemia is rare in patients with Wilms' tumor [ 10]. Clear cell sarcoma of the kidney was also once considered a sarcomatous variant of Wilms' tumor and is now recognized as a distinct neoplastic entity. It accounts for approximately 4% of all childhood renal tumors and has a mortality rate of approximately 50% [8]. Referred to as "bone metastasizing renal tumor of childhood" by Marsden et al., it has a reported incidence of bone metastases of 76% [ 11 ]. R T K rarely metastasizes to the skeletal system, with osseous involvement reported in less than 5% of cases [1]. Wilms' tumor also rarely metastasizes in this manner with reported incidences of osseous involvement ranging from 0.5 to 13% [12]. In both of our cases of RTK, large bulky masses with poorly defined margins and associated calcification were demonstrated by US and CT. This is in contrast to classic Wilms' tumor which commonly is seen on CT as a well-circumscribed mass with "clean" margins and a prominent pseudocapsule composed of compressed, enhanced renal tissue. Less commonly, Wilms' tumor exhibits an infiltrative growth pattern with a resultant mass that is ill-defined and poorly marginated [8]. It is apparent that the poorly defined margins of R T K are not helpful in differentiating this neoplasm from other renal tumors of childhood. It has recently been emphasized that R T K characteristically assumes a medial location within the kidney, whereas Wilms' tumor tends to arise in the outer cortex [1]. Although calcification was demonstrated on US and CT in both of our cases of RTK, this, however, could not be confirmed histologically in case 1, since only random biopsies were obtained. In the second case, calcifications were demonstrated in the portions of the kidney uninvolved by tumor. This may be secondary to the associated hypercalcemia. The exact significance of this finding is uncertain and it
97
S.Z.H. Jafri et al.: Rhabdoid Tumor of the Kidney has not been described previously with R T K . Calcification is u n c o m m o n in W i l m s ' tumor, occurring in only 3-5% o f patients. Retroperitoneal adenop a t h y was a significant finding in both o f our cases. This finding usually indicates a p o o r prognosis. Local metastasis to regional l y m p h nodes has frequently been observed in W i l m s ' tumor. In a small n u m ber o f cases o f W i l m s ' t u m o r , fat has b e e n d e m o n s t r a t e d in the renal mass on CT. T o our knowledge this has not been seen with R T K [8].
Summary In s u m m a r y , two cases o f R T K are described, both in very y o u n g children who presented with a b d o m inal masses. It is apparent from the clinical and pathological features o f R T K that this neoplasm comprises a discrete entity which should be considered in the differential diagnosis o f a large renal mass presenting in a y o u n g child. T h e radiographic features, however, do not help in distinguishing this neoplasm from other renal neoplasms o f childhood. This t u m o r has a dismal prognosis; no effective treatment has yet been devised. The high mortality rate o f R T K necessitates additional studies to further elucidate the pathobiology o f this t u m o r a n d to develop a treatment protocol which is effective in its management.
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