What Is a Renomedullary Interstitial Cell Tumor?
A renomedullary interstitial cell tumor, also known as renal hamartoma or medullary fibroma, is an uncommon benign kidney tumor. It was named renomedullary interstitial cell tumor based on biological structure characteristics that resemble renomedullary interstitial cells. It is often found accidentally during autopsy or kidney resection for other reasons. This is seen localized in the medulla, and the lesion is usually small (usually less than five millimeters); therefore, it is hardly detected clinically. However, rare cases have been reported with large masses in the kidney. Most of the renomedullary interstitial cell tumors present no clinical symptoms. But, in some cases, hematuria (blood in urine) and urosepsis (urinary tract infection) have been reported.
What Is the Incidence of Renomedullary Interstitial Cell Tumor?
The incidence of renomedullary interstitial cell cancer increases with age. Most tumors occur in the renal medulla and sometimes in the renal cortex. It is rare in people less than 25 years and most commonly affects people older than 50 years. It affects both males and females equally. Also, no specific ethnic or racial predilection is detected.
What Are the Clinical Features of the Renomedullary Interstitial Cell Tumor?
The clinical feature of a renomedullary interstitial cell tumor depends on the location and size of the tumor. Normally, small tumors do not present with symptoms and remain silent for an entire lifetime and are detected in an autopsy, whereas patients with large tumors can present with signs and symptoms. So, each individual with a renomedullary interstitial cell tumor will have variations in the signs and symptoms. This tumor usually affects a single kidney, and rarely, bilateral kidneys can get involved with multiple lesions. Bilateral tumors are prevalent in elderly people. The clinical feature of renomedullary interstitial cell tumors are
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Hematuria (blood in the urine).
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Hydronephrosis (excess accumulation of fluid in the kidney due to urine build-up)
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Recurrent urinary tract infection.
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Flank pain.
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Large tumors can increase blood pressure.
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As the tumor grows, it starts to compress the adjacent organs and affect their function. However, they are not known to infiltrate them.
What Are the Macroscopic and Microscopic Features of a Renomedullary Interstitial Cell Tumor?
Renomedullary interstitial cell tumor appears round to oval in shape, well-circumscribed, homogenous, tan to white in color, and not encapsulated tumor. The size of the tumor varies from one millimeter to one centimeter. But a tumor of even eight centimeters has been reported in the medical literature. They often appear as a single tumor, but multiple tumors affecting both kidneys are reported in some cases. The prevalence is equal for both sexes.
Microscopically renomedullary interstitial cell tumor cells are small, stellate, spindle-shaped, and arranged in a radiating pattern. It has bland nuclei embedded in a loose or dense collagenous basophilic stroma. The chromatin is open and is hyperchromasia which suggests malignancy. Some tumors appear glassy and translucent or contain protein deposits called amyloid. The tumor contains some degree of entrapped normal renal tubules and eosinophilic collagen bundles, mostly in the periphery of the tumor. Cystic dilated tubules were present in rare cases.
What Is the Differential Diagnosis of Renomedullary Interstitial Cell Tumor?
Renomedullary interstitial cell tumors can be misdiagnosed with metanephric stromal tumors and mixed epithelial and stromal tumors (MEST). By knowing the special characteristics of each tumor, a diagnosis can be made correctly.
1) Metanephric Stromal Tumor - They have characteristic onion-skin rings formation, which means concentric rings or collarettes of stromal cells around entrapped blood vessels or renal tubules in a myxoid background. Unencapsulated infiltrative of spindle and epithelioid cells can be noted. This tumor is rare in adults.
2) Mixed Epithelial and Stromal Tumor (MEST) - It appears as a larger mass lesion with randomly distributed epithelial components throughout the tumor and the stroma. It has positive estrogen and progesterone receptors with fibroblastic or myofibroblastic spindle cell differentiation and variable degrees of smooth muscle.
3) Scar - The lesion will not be well circumscribed and will be less basophilic. There can be a history of renal stones, poor renal function, or surgical history. This can occur mostly due to inflammation.
How Is Renomedullary Interstitial Cell Cancer Diagnosed?
Renomedullary interstitial cell tumor is often detected during autopsies, meaning it remains silent or goes unnoticed by individuals. In some cases, it is accidentally diagnosed during diagnosis undertaken for other health conditions. Later, a biopsy is done to rule out cancer. If renomedullary interstitial cell cancer is suspected, then a complete medical history and physical examination are carried out, followed by a few tests and procedures, including:
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Complete blood counts test to detect polycythemia.
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Urine analysis is performed to detect blood cells in the urine.
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X-ray of the abdomen.
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Kidney function test.
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CT (computed tomography) scan of the abdomen - It shows a well-defined mass.
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MRI (magnetic resonance imaging) scans of the abdomen - The high-quality MRI pictures may reveal the tumor's presence.
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Ultrasound scan of the abdomen
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Intravenous pyelogram (IVP) - A dye is injected intravenously, and the image of the kidney is obtained.
The tests can be used to produce an initial diagnosis. However, a tissue biopsy is required to make a definitive diagnosis and begin the initial treatment. The biopsy sample can be taken in various ways, which include:
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Fine needle aspiration (FNA) of the kidney tumor.
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Core biopsy of the kidney tumor.
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Open biopsy of the kidney tumor.
The collected tissue sample is then taken to a laboratory for further studies. The specimen is initially studied using normal staining with hematoxylin and eosin staining. Later, if additional studies require immunohistochemical stains, molecular testing, and electron microscopic studies are performed.
What Is the Treatment for Renomedullary Interstitial Cell Tumor?
The treatment options for renomedullary interstitial cell tumors depend on the presenting symptoms; in most cases, the tumor does not produce any symptoms and remains asymptomatic with small-sized tumors, so healthcare professionals may suggest a wait-and-watch approach. If symptoms are present, then surgical intervention with complete excision is carried out. It can also reduce the risk of tumor recurrence.
Conclusion
A renomedullary interstitial cell tumor is a rare benign tumor of the kidney. It is mostly asymptomatic and often detected during autopsies. In rare cases, patients present with symptoms like flank pain, hematuria (blood in urine), and urinary tract infections. It is also diagnosed accidentally in most cases, after which a biopsy is carried out to confirm the diagnosis. If there is no presentation, no treatment is carried out; surgical intervention is required in other cases.
