Adrenal myelolipoma: An incidental and rare benign tumor in children.

Myelolipoma is a rare benign tumor of adrenal gland and rarer in children. Myelolipoma contains adipose tissue and myeloid precursor producing white blood cells (WBC), red blood cells (RBC) and megakaryocytes. Asymptomatic tumor does not require treatment whereas symptomatic tumor needs operation. We are reporting a rare adrenal myelolipoma in a child with review of literature.

INTRODUCTION

Adrenal myelolipoma is a tumor-like lesion composed of variable amounts of mature adipose tissue and bone marrow elements. In spite of WBC and RBC precursors such as megakaryocytes, it does not serve as a hematopoietic source. Giercke in 1905 first described and 24 years later, Oberling coined the term ‘myelolipoma’. It usually affects patients in their 4th to 6th decades. Only two cases under the age of 16 are reported and to the best of our knowledge, this patient is the youngest pediatric case of adrenal myelolipoma reported in the English literature.

CASE REPORT

An 11-year-old girl presented with recurrent pain abdomen for 1 year, which was gradually increasing in frequency and severity for last 5 months. There were no other associated symptoms. Ultrasonography (USG) of abdomen showed a well-encapsulated and hypo echoic lesion in right suprarenal region measuring 27.1 × 24.3 mm. Contrast enhanced computed tomography (CECT) scan of abdomen confirmed the lesion to be arising from right adrenal gland with fat density measuring 1.8 × 2.3 cm [Figure 1]. Opposite adrenal gland and kidney were normal. There was also a calcification in the peripheral part of the lesion. Clinical examination, complete hemogram, blood biochemistry, urine microscopy were normal. The mass was removed surgically and was sent for histopathology. It measured 2 cm × 3cm × 1cm. Gross examination of the specimen showed reddish yellow colored friable mass, soft in consistency; and on microscopy, islands of hematopoietic tissue were found scattered among the fat cells [Figure 2].

Figure 1

CECT reveal small fat containing lesion in right adrenal suggestive of myelolipoma

Figure 2

Histopathology showing fat lobules (F) and megakaryocyte (M)

DISCUSSION

Adrenal myelolipoma is a tumor-like lesion composed of variable amounts of mature adipose tissue and bone marrow elements. In spite of WBC and RBC precursors such as megakaryocytes, it does not serve as a hematopoietic source.

Myelolipoma may occur in retroperitoneum around kidney and pre-sacral space or in liver; however, adrenal gland is the most common site.[1] Reported incidence of this tumor in autopsy series is varying between 0.03% to 0.8%.[2] Unilateral involvement is more common. Size of the tumor usually less than 5 cm and giant myelolipoma is rare. Both genders are almost equally affected.

Most of the cases of myelolipomas are asymptomatic. Usually diagnosed incidentally at imaging for other purposes and the reported incidence are reaching up to 7% of the adrenal masses. Majority of incidentally discovered myelolipomas are small and asymptomatic though large symptomatic lesions are also reported but in adult population.

Symptoms may be due to large tumor causing the pressure effect, tumor necrosis and intralesional hemorrhage. Spontaneous retroperitoneal hemorrhage is usually the most common complication of adrenal myelolipoma. Malignant potential of adrenal myelolipoma has not been reported. In our study, the child presented with pain abdomen and, on investigation diagnosis was confirmed.

The lesion is itself hormonally inactive but may be associated with metabolically active adrenal lesion like Cushing syndrome, Conn's syndrome, congenital adrenal hyperplasia etc.[3] Myelolipoma can be regarded as an exception to the mandatory metabolic work-up of a newly discovered adrenal mass.[4]

Etiology of adrenal myelolipoma is unknown till now. Large myelolipoma usually associated with hematological disorders like hereditary spherocytosis, thalassemia intermedia, thalassemia major, sickle cell anemia and usually bilateral. Such large tumor may be due to external stimulus of erythropoietin. If we get a case of large or bilateral adrenal myelolipoma we have to investigate for chronic hematological disorders. Before removal the of tumor, it may be necessary for bone marrow transplantation to avoid aggravation of hemolytic anemia.

Myelolipomas are usually small and non-functional in nature with unclear etiology. Most accepted theory regarding etiologies are that it arises in response to infection, stress or necrosis causing metaplasia of reticuloendothelial cells of the capillaries of adrenal gland.[5]

CECT is the investigation of choice for confirmation of diagnosis. CECT is preferable for identification of adrenal myelolipoma than MRI. Focal fat density, peripheral calcification and hemorrhage within the tumor can be better identified with CECT scan. MRI scan may be helpful for detection of organ of origin of large myelolipoma.

Myelolipoma contains adipocytes with hematopoietic elements, consisting of myeloid and erthyroid precursors, as well as, megakaryocytes. These hematopoietic elements are scattered in the adrenal tissue and separated by sheets and large clusters of mature adipocytes admixed with hemorrhagic foci. The presence of macroscopic fat in an adrenal mass is virtually diagnostic of myelolipoma.

Though open surgery is the classical method, laparoscopic adrenalectomy has now become the standard of care for the treatment of functioning and non-functioning adrenal tumors, introduced by Gagner in 1992.

Asymptomatic myelolipomas are treated conservatively. Surgery is usually reserved for symptomatic lesions.[6] Laparoscopic adrenalectomy is now a preferred option with good outcome.

CONCLUSION

Adrenal myelolipomas are rare benign tumors of adrenal gland and extremely rare in children. CT scan is useful adjunct for confirming the diagnosis. Small asymptomatic myelolipomas can be treated conservatively but the symptomatic one should be treated with surgical excision and/or adrenalectomy.