Renal medullary carcinoma is a highly aggressive kidney tumor occurring predominantly in young patients with sickle cell trait or sickle cell disease. It originates from the renal medulla and demonstrates an infiltrative growth pattern. Prognosis is extremely poor, with most patients presenting with metastatic disease at diagnosis. Median survival is less than 5 months, and response to chemotherapy is limited. It shares morphological similarities with collecting duct carcinoma but the sickle cell association is distinctive.
Age Range
10-40
Peak Age
22
Gender
Male predominant
Prevalence
Rare
Renal medullary carcinoma originates from the distal nephron segments of collecting ducts, specifically the calyceal epithelial cells in the renal papilla. Chronic medullary hypoxia and ischemia in sickle cell trait/disease are thought to contribute to tumorigenesis. Loss of SMARCB1 (INI1) tumor suppressor gene is a characteristic molecular feature. The tumor grows rapidly, infiltrates the renal sinus, and shows early lymphatic and hematogenous dissemination. Retroperitoneal lymph nodes, lungs, and liver are the most common metastatic sites.
In a young patient (typically 10-40 years) with sickle cell trait or disease, an infiltrative hypovascular heterogeneously enhancing mass originating from the renal medulla and infiltrating the renal sinus is the most important diagnostic clue for renal medullary carcinoma. The absence of arterial hypervascularity, unlike clear cell RCC, is an important distinguishing feature.
Heterogeneous, mildly hyperdense mass centered in the renal medulla, largely preserving renal contours but infiltrating the renal sinus. The mass is typically ill-defined with indistinct borders between normal renal parenchyma and tumor. Necrotic areas appear hypodense.
Report Sentence
A heterogeneous mass centered in the renal medulla with infiltration of the renal sinus containing areas of necrosis is identified.
In corticomedullary phase, the mass demonstrates markedly hypoenhancing pattern compared to surrounding normal renal parenchyma. Heterogeneous enhancement with necrotic/cystic areas showing no contrast uptake. Renal sinus fat invasion and perinephric extension are best evaluated in this phase.
Report Sentence
In corticomedullary phase, the mass shows markedly reduced enhancement compared to surrounding parenchyma with heterogeneous architecture and necrotic areas.
In nephrographic phase, the mass shows persistent hypoenhancement against homogeneously enhancing renal parenchyma. This phase provides optimal contrast for delineating tumor margins, assessing renal sinus invasion and renal vein involvement. Perinephric stranding and Gerota fascia thickening indicate extracapsular extension.
Report Sentence
In nephrographic phase, the mass remains markedly hypodense compared to surrounding parenchyma with renal sinus invasion and perinephric fat stranding.
In portal venous/delayed phase, retroperitoneal lymphadenopathy is seen as enlarged renal hilar and para-aortic lymph nodes. Metastatic lymph nodes may show heterogeneous enhancement and central necrosis. Inferior vena cava and renal vein thrombosis should be assessed in this phase.
Report Sentence
Pathologically enlarged lymph nodes with central necrosis are seen in the renal hilar and para-aortic retroperitoneal regions.
On T2-weighted images, the mass demonstrates heterogeneous signal intensity. Solid components show intermediate-to-low T2 signal while necrotic and cystic areas show high T2 signal. A reticular (net-like) pattern is characteristic of medullary carcinoma, reflecting the admixture of desmoplastic stroma with necrotic areas.
Report Sentence
On T2-weighted images, an infiltrative mass with heterogeneous signal intensity containing solid and necrotic components is seen in the renal medulla.
On diffusion-weighted images, solid tumor components demonstrate marked diffusion restriction (bright on high b-value images, low signal on ADC maps). Necrotic areas do not show diffusion restriction. ADC values are typically low (0.8-1.2 × 10⁻³ mm²/s), reflecting high cellularity and nuclear-to-cytoplasmic ratio.
Report Sentence
Diffusion-weighted images show marked diffusion restriction in solid tumor components with low ADC values.
On B-mode ultrasound, a predominantly heterogeneous mass with ill-defined borders is seen in the renal medulla. The mass is generally hypoechoic compared to renal parenchyma, but necrotic/cystic areas may show anechoic appearance. Obliteration of renal sinus echo and distortion of calyces is characteristic.
Report Sentence
B-mode ultrasound demonstrates an ill-defined, heterogeneous, predominantly hypoechoic mass in the renal medulla with obliteration of the renal sinus echo.
On FDG PET-CT, the primary tumor shows intense FDG uptake (SUVmax typically >10). Metastatic lymph nodes and distant metastases also demonstrate increased FDG uptake. Delayed images improve assessment of tumor uptake due to physiological FDG excretion by renal parenchyma. PET-CT is valuable for staging and treatment response assessment.
Report Sentence
FDG PET-CT demonstrates intense FDG uptake (SUVmax >10) in the primary renal mass with increased metabolic activity in retroperitoneal lymph nodes and distant sites.
Criteria
SMARCB1 (INI1) loss, sickle cell trait/disease association, reticular growth pattern, high-grade cytology
Distinct Features
Most common form. Prominent infiltrative growth, dense desmoplastic stroma, neutrophil infiltration, and sickle-shaped erythrocytes are histologically typical. On imaging, medullary location and renal sinus invasion are prominent.
Criteria
Complete SMARCB1 loss (confirmed by immunohistochemistry), may or may not have sickle cell association, separate entity in WHO 2022 classification
Distinct Features
Rare variant that can occur without sickle cell association. Imaging features are similar to classic form but clinical context (absence of sickle cell) may be distinguishing. Prognosis is similarly poor as classic form.
Criteria
Form where >50% of tumor volume consists of necrosis or cystic degeneration with thin peripheral solid tumor tissue remaining
Distinct Features
Due to extensive necrosis, imaging shows limited solid component with prominent cystic/necrotic areas. Thin peripheral enhancing solid tumor rim is critical for diagnosis. May be confused with infected collection or complicated cyst, but medullary location and clinical context are distinguishing.
Distinguishing Feature
Collecting duct carcinoma is also a medullary infiltrative mass but lacks sickle cell association and typically occurs in older patients. SMARCB1 loss is seen in medullary carcinoma while it is retained in collecting duct carcinoma.
Distinguishing Feature
Urothelial carcinoma grows from the renal pelvis into the medulla, showing pelvicalyceal filling defect on excretory phase. Medullary carcinoma originates from parenchyma. Urothelial carcinoma lacks sickle cell association and typically occurs in patients >60 years.
Distinguishing Feature
Renal lymphoma typically shows bilateral, multifocal, and homogeneously hypoenhancing masses. Medullary carcinoma is unilateral, heterogeneous, and contains prominent necrosis. Lymphoma usually occurs in the context of systemic disease without sickle cell association.
Distinguishing Feature
Clear cell RCC is a cortically located, hypervascular mass with prominent arterial phase enhancement. Medullary carcinoma is medullary in location, hypovascular, and infiltrative. RCC typically occurs in patients >50 years, while medullary carcinoma affects young sickle cell carriers.
Urgency
emergentManagement
surgicalBiopsy
NeededFollow-up
specialist-referralRenal medullary carcinoma is a highly aggressive tumor, with most patients presenting with advanced disease at diagnosis. Urgent urology and oncology consultation is required. Radical nephrectomy is the primary treatment, but curative surgery may not be feasible due to metastatic disease in most patients. Response to chemotherapy is limited; limited success has been reported with high-dose methotrexate-based regimens and immunotherapy. Biopsy is needed for confirmation of SMARCB1 loss. Concurrent sickle cell disease management is required.
Renal medullary carcinoma is one of the most aggressive kidney tumors with a median survival of less than 5 months. It should be considered when a medullary renal mass is seen in young Black patients with sickle cell trait. Response to chemotherapy is limited.