Adrenal incidentaloma

We describe a patient with an incidental adrenal myelolipoma associated with biochemical evidence of Cushing's syndrome who lacked the physical stigmata of cortisol excess (subclinical Cushing's syndrome). Pathologic examination revealed the presence of adrenocortical cells mixed with myelolipomatous tissue. Although cases of clinically evident Cushing's syndrome due to adrenal myelolipomas have been reported previously, to our knowledge this is the first report associating adrenal myelolipoma and subclinical Cushing's syndrome.

(Arch Pathol Lab Med. 1997;121:735-737)

In recent years, the wider availability of sensitive imaging techniques has allowed the frequent discovery of unsuspected asymptomatic adrenal masses. When a refined laboratory investigation is performed, mild cortisol hypersecretion insufficient to cause overt Cushing's syndrome is found in a notable percentage of these patients. Adrenal incidentalomas causing subclinical Cushing's syndrome are presumed to be adrenal adenomas. Here we report the case of an adrenal incidentaloma inducing subclinical hypercortisolism in which pathologic examination of the tumor showed an adrenal myelolipoma. Although myelolipomas have been rarely reported to cause overt adrenocorticotropin-independent Cushing's syndrome, 1-4 to our knowledge, this is the first report associating preclinical Cushing's syndrome and adrenal myelolipoma.

REPORT OF A CASE

A 65-year-old woman was referred to our hospital for the evaluation of an adrenal incidentaloma. Past medical history was notable for craniectomy due to parietal meningioma, peptic ulcer, and hypertension of 3 years' duration. Medications included captopril, 50 mg daily, and phenytoin, 300 mg daily. The patient was completely asymptomatic. She originally underwent an abdominal ultrasonography during evaluation of mild microcytic anemia. An unexpected mass was disclosed in her right adrenal gland, and she was referred to our endocrinology department.

On admission the patient was 153 cm tall and weighed 75.4 kg. Physical examination was unremarkable. Blood pressure on captopril treatment was 160/90 mm Hg.

Laboratory investigations revealed normal catecholamines, metanephrines, and vanillylmandelic acid in a 24-hour urine specimen. The patient's serum potassium level was 4.9 mmol/L. Baseline plasma concentrations of 17-hydroxyprogesterone, androstendione, and free testosterone were within normal ranges. Levels of dehydroepiandrosterone sulfate were near the low limit of normality. Three consecutive 24-hour urine samples coincided to show high urinary free cortisol excretion. Circadian rhythm in plasma cortisol secretion was preserved, but morning plasma cortisol was not suppressed by 1 mg of dexamethasone given at midnight. Because false-positive results of the dexamethasone suppression test may occur in patients receiving phenytoin therapy, an overnight "super-high" dose suppression test was performed with 16 mg of dexamethasone, and normal suppression of cortisol was then achieved. Adequate response of adrenocorticotropin and cortisol to corticotropin-releasing hormone stimulation (100 (mu)g intravenously) were recorded. Endocrine assessment is summarized in Table 1.

Computed tomographic scanning identified a tumor in the right adrenal gland, measuring 7 cm in diameter. The lesion was well delimited and consisted of a large fat-density area, but also contained a component of soft tissue with positive attenuation (Fig 1).

A laparotomy was performed. The tumor was removed, without extirpation of adjacent gland, which showed a nonpathologic appearance. It was a well-encapsulated oval mass, which weighed 90 g and measured 5.2 cm in maximum diameter. Its cut surface was yellow (Fig 2, left).

Microscopic examination revealed abundant, mature, fatty tissue along with islets of normal hematopoietic cells. The tumor was confined by a capsule of connective tissue. Rests of normal adrenal cortex adhered to the outer surface of the capsule. The hematopoietic component included all three myeloid cell lines, granulocytes, erythrocytes, and megakaryocytes, as well as lymphocytes, plasma cells, and reticuloendothelial cells. Cells of granulocytic line were represented by promyelocytes and neutrophils, exhibiting positive staining with chloracetate esterase. Lymphoid cells expressed common leukocyte antigen (CD45, Dako-LC). Nest and cordlike arrangements of fascicular and reticular cells were intermingled with elements of myelolipoma (Fig 2, right). Epithelial compound accounted for about 10% of the tumor's content.

Determination of the urinary free cortisol level after surgery was 104.8 nmol/24 h, and the patient's basal plasma adrenocorticotropin level raised to 12.6 pmol/L.

COMMENT

Myelolipoma of the adrenal gland is a benign, usually silent neoplasm containing both adipose and hematopoietic tissues. It has been found in 0.2% of nonselected autopsies.5 Until widespread use of high-resolution anatomical imaging procedures, diagnosis of adrenal myelolipomas was limited to rare cases producing symptoms of excessive growth or intratumoral hemorrhage. In the last few years, with the availability of computed tomography, magnetic resonance imaging, and ultrasonography, silent adrenal masses have been detected with increased frequency, and myelolipomas, which represent 7% to 15% of the socalled adrenal incidentalomas,6 are thereby increasingly diagnosed premortem.

In exceptional cases, adrenal myelolipomas have been diagnosed because of their association with different endocrine disorders. Fortuitous finding of these tumors in patients with Cushing's disease, Nelson's syndrome, and congenital adrenal hyperplasia has led some authors to postulate that adrenocorticotropin oversecretion could play a role in the pathogenesis of adrenal myelolipomas.7 To date, causal relationship between excessive adrenocorticotropin levels and myelolipomas has not been definitively demonstrated.

On the other hand, functioning myelolipomas have been found to cause adrenal hypersecretory syndromes themselves. These cases seem to be the result of the presence of intratumoral hyperplastic or adenomatous adrenal cells mixed with elements of the myelolipoma. These combined adrenal and myelolipomatous tumors are typically silent, but they have been reported to induce hyperaldosteronism,8 pheocromocytoma,9 and adrenocorticotropin-independent Cushing's syndrome.1-4 Characteristics of four reported cases of Cushing's syndrome due to primary adrenal myelolipomas are summarized in Table 2. In three of these cases,1-3 the diagnosis was suspected because of clinically evident Cushing's syndrome, but the remaining case was also disclosed by an incidental finding of an adrenal mass during a radiologic abdominal exploration for a problem unrelated to adrenal function.4

In our patient, endocrine assessment demonstrated persistent high urinary cortisol excretion. Surgical removal of the incidentaloma achieved normalization of urinary cortisol levels, and its pathologic examination resembled the picture found in previous reports of Cushing's syndrome due to adrenal myelolipoma.

Apart from hypertension and obesity, however, clinical signs and symptoms of classic Cushing's syndrome were absent in our patient. Concurrent intake of phenytoin prevented exclusion of a subtle alteration in plasma cortisol suppressibility, but it does not explain the increased levels of urinary free cortisol. The rhythm of cortisol secretion and adrenocorticotropin response to stimulation with corticotropin-releasing hormone were normal.

It is now well documented that many adrenal incidentalomas, previously thought to be nonfunctioning, display autonomous glucocorticoid secretion, although they produce adrenocortical hormones in amounts insufficient to cause clinically apparent disease.5,9 In these cases, results of endocrine evaluation are variable. Loss of circadian rhythm and failure of the suppression of plasma cortisol following the administration of dexamethasone typically occur before hypercortisolism is present,6,10 but isolated patients have displayed high urinary free cortisol and low levels of dehydroepiandrosterone sulfate as the only disorders in adrenocortical function,10 such as occurred in our case.

Adrenal incidentalomas causing subclinical Cushing's syndrome are presumed to be cortical adenomas, but most of these tumors are not surgically removed and definitive pathologic diagnosis is therefore not established. We have reported a case of subclinical Cushing's syndrome induced by an adrenal adenomyelolipoma. Taking into account that some of these tumors lack typical radiologic features,11 it is possible that they may be responsible for other cases of preclinical Cushing's syndrome.

References

1. Kanj HA, Noronha J, D'Aguillo AF, Amorosa JK, Amorosa LF. Bilateral adrenal myelolipomas with Cushing's syndrome. JAMA. 1988;259:3034-3036.

2. Vyberg M, Sestoft L. Combined adrenal myelolipoma and adenoma associated with Cushing's syndrome. Am J Clin Pathol.1986;86:541-545.

3. Jenkins PJ, Chew SL, Lowe DG, Reznek RH, Wass JA. Adrenocorticotrophinindependent unilateral macronodular adrenal hyperplasia occurring with myelolipoma: an unusual cause of Cushing's syndrome. Clin Endocrinol (OxO. 1994;41:827 830.

4. Ito T, Asano K, Nomura K, et al. Two cases of adrenal myelolipoma. Acta Pathol jpn. 1992;42:221-226.

5. Abecassis M, McLoughlin MJ, Langer B, Kudlow JE. Serendipitous adrenal masses: prevalence, significance, and management. Am ) Surg. 1985;149:783788.

6. Kloos RT, Gross MD, Francis IR, Korobkin M, Shapiro B. Incidentally discovered adrenal masses. Endocr Rev.1995;16:460-484.

7. Oliva A, Duarte B, Hammadeh R, Ghosh L, Baker RJ. Myelolipoma and endocrine dysfunction. Surgery 1988;103:711-717.

8. Escuin F, Gomez P, Martinez I, Perez-Fontan M, Selgas R, Sanchez-Sicilia L. Angiomyelolipoma associated with bilateral adrenocortical hyperplasia and hypertension. J Urol.1985;133:655-657.

9. Ukimura O, Inui E, Ochiai A, Kojima M, Watanabe H. Combined adrenal myelolipoma and pheochromocytoma. J UroL 1995;254:1470.

10. Osella G, Terzolo M, Borretta G, et al. Endocrine evaluation of incidentally discovered adrenal masses (incidentalomas). J Clin Endocrinol Metab. 1994;79: 1532-1539.

11. Musante F, Derchi LE, Zappasodi F, et al. Myelolipoma of the adrenal gland: sonographic and CT features. AJR Am J Roentgenol.1988;151:961-964.

Mauro Boronat, MD; Amalia Moreno, MD; Santiago Ramon y Cajal, MD; Eva Pineda, MD; Tomas Lucas, MD; Javier Estrada, MD

Accepted for publication February 19, 1997.

From the Departments of Endocrinology (Drs Boronat, Pineda, Lucas, and Estrada) and Pathology (Drs Moreno and Ramon y Cajal), Clinica Puerta de Hierro, Universidad Autonoma, Madrid, Spain.

Reprint requests to Servicio de Endocrinologia, Clinica Puerta de Hierro, C/San Martin de Porres, 4, 28035 Madrid, Spain (Dr Boronat).

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