Introduction:
Myelolipoma of the kidney is an extremely rare disease comprising adipose tissue in combination with hematopoietic substances in varying ratios. Adrenal glands are the most common location where myelolipoma can be seen. However, extra-adrenal myelolipomas in other sites like the retroperitoneum, pelvis area, mediastinum, and presacral region can also be found. The incidence of finding this entity extrarenal is the least. Myelolipomas show female predilection.
Generally, myelolipomas can be seen in people of age 50 to 70. Myelolipoma is the most known entity type and is a lipomatous adrenal tumor. The reason behind its formation is under debate. Amongst all the cases ever reported, the myelolipoma occurring in the adrenal gland was more common than its occurrence in other organs. Some theories hypothesize that this disease comes under the hamartoma entity or can be from the group of choristomatous hematopoietic stem cells that moved into other sites during intrauterine life. Some other theories proposed that clonal cytogenetic abnormality was found in myelolipoma, which suggests it had renal tumor origin.
What Is A Myelolipoma?
Kidney myelolipoma disease can rarely be seen in existence. It constitutes adipose tissue along with hematopoietic substances in varying proportions. Myelolipoma on other sites is not more common than in the adrenal gland. The adrenal gland is the most common site for this entity. Myelolipoma involving the kidney, renal sinus, and perirenal tissue can be diagnosed while investigating other diseases. Symptoms not specific to myelolipomas, such as pain in the loin and abdomen, hematuria, and bloating, can be seen. Female predilection is seen for myelolipoma and occurs most often from the fifth to the seventh decade of life. It is a lipomatous adrenal tumor. Radiologically, the images show a renal mass having a fatty dense attenuation on the Computed tomography scan or in the magnetic resonance imaging and also show the least enhancement. Diagnosis is confirmed by studying the specimen and finding the mixed adipose tissue with normal hematopoietic cells. This is an entity that may be present along with other diseases.
What Is The Pathophysiology Of Myelolipoma?
The pathophysiology of myelolipoma needs to be clarified and is still being researched. There are differences of opinion between various researchers regarding the pathophysiology of myelolipoma. It is stated in a few of the theories that endocrine dysfunction initiates a triggering effect that helps in the differentiation and development of either the remnant of hematopoietic stem cells or the remnant of ectopic adrenal cells. Also, some theories noticed clonal cytogenetic abnormalities, leading to the hypothesis that myelolipoma originated from a tumor. It has also been stated that myelolipomas can originate from bone marrow cells, which eventually express the poor linkage of myelolipoma with the transferred erythroid cells.
What Do The Various Radiological Investigations State?
1. Ultrasound Scan:
An ultrasound scan of the renal tract, abdomen, and pelvic area can detect a lesion inside the kidneys or surrounding the kidneys, which leads the physician toward further investigation to know the cause, type, and origin of the lesion. It also provides us with information about the lesion's size, site, and shape. If a contrast-enhanced ultrasound scan (CEUS) of the lesion is observed, then it can be seen that the non-contrast enhancement of the lesion surrounds the renal hilum. Biopsy or ultrasound-guided aspiration cytology of the lesion can also be performed.
2. Computed Tomography Scan:
A computed tomography scan (CT) can be carried out to investigate or diagnose the myelolipoma of the kidney. The scan of the abdominal or pelvic region can show a solid mass with fat density attenuation in the kidney. The lesions can be observed near the hilum of the kidney or may be present peripherally. The lesions can also be present surrounding the ureters. Ureters are tube-like elastic structures that provide a connection between the kidneys and the urinary bladder. Associate lesions that are present in the area can also be seen in the scans.
3. Magnetic Resonance Imaging (MRI) Scan:
The magnetic resonance imaging scan (MRI) provides the physician with the images that help them identify the lesion and confirm the diagnosis of myelolipoma of the kidney. A solid mass in the kidney with fat density attenuation can be seen in the abdominal or pelvic region. Also, if there are any other associated lesions in the kidney or surrounding the kidney, then they can also be seen. Mostly, they are benign in nature, which is why they can be seen as non-contrast-enhanced images. This type of scan or imaging is used to survey the progress of small myelolipomas managed conservatively.
4. Selective Renal Artery Angiography:
Selective renal artery angiography can be called an interventional radiologic investigation used to assess renal cancers and angiomyolipoma of the kidney.
What Do The Various Radiological Investigations State?
After the diagnosis of the myelolipoma is confirmed, the size and the site of the lesion are thoroughly studied. The following treatments can be used to treat myelolipoma:
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Treatment in a conservative way, along with radiological imaging surveillance.
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Partial nephrectomy with an open or laparoscopic approach.
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An open or laparoscopic approach by performing radical nephrectomy.
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The lesion is excised if it is present around the kidneys or ureters.
What Are The Differential Diagnosis Of Myelolipoma?
- Angiomyolipoma: An angiomyolipoma is one of the most common benign lesions of the kidney. It is predominantly fatty and looks like lesions such as liposarcoma and myelolipoma.
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Liposarcoma: This lesion mostly occurs in the sixth decade of life and does not show any gender predilection. These types of lesions are generally asymptomatic until they enlarge.
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Extramedullary Hematopoietic Tumors: An extramedullary hematopoietic tumor is characterized by hepatosplenomegaly, anemia, and abnormal blood smears. They show the predominance of hematopoietic cells and also the erythroid hyperplasia.
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Other lesions like lipomatosis, transitional cell carcinomas, renal cell carcinoma, and metastatic tumors can also be considered under the differential diagnosis of myelolipoma.
Conclusion:
Myelolipoma is a benign, rare entity that can be treated and shows a good prognosis. It is made up of adipose tissue and hematopoietic substances. It can appear in both genders but shows female predilection. It can be seen in the adult age group from the fifth to the eighth decade but is mostly found in the seventh decade. It is mostly asymptomatic, and it is diagnosed while investigating any other condition.
