Case Report

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A 22-year-old woman presented with a 3-month history of postpartum amenorrhea. Physical examination showed a blood pressure of 190/100 mm Hg, moon facies, and truncal obesity. Prominent purple striae covered her abdominal and chest walls. No goiter was palpable. Laboratory data included serum cortisol concentrations of 966 nmol/L at 0800 h (normal, 138 to 552 nmol/L) and 828 nmol/L at 2000 h (normal, 55 to 414 nmol/L). The plasma ACTH level at 0800 h was 60 pmol/L (normal, 2.3 to 13.8 pmol/L). Urinary free cortisol excretion was 1269 nmol/24 h (normal, 30 to 300 nmol/24 h). Dexamethasone administration of up to 16 mg daily in four equally divided doses did not significantly suppress serum cortisol and plasma ACTH levels or urinary free cortisol excretion. Cortisol and ACTH levels were both determined using commercially available kits (cortisol: DPC, Los Angeles, California; ACTH: Nichols Institute, San Juan Capistrano, California).

Contrast-enhanced pituitary computed tomographic (CT) scans were normal. Abdominal CT scans and magnetic resonance imaging studies showed that both adrenal glands were diffusely enlarged but that the pancreas seemed normal. An enhanced axial CT scan of the chest with 5-mm-thick slices showed no abnormality. Somatostatin receptor imaging done after intravenous administration of 20 µg of Indium-111-pentetreotide (222 MBq) showed a focus of increased activity in the left upper lobe, parahilar in location Figure 1 a, as early as 4 hours after the injection of the tracer. This focus was evident for at least an additional 20 hours thereafter. Repeat CT scanning of the chest with coronal reconstruction of the left upper lobe showed a central 1-cm rounded mass occluding a subsegmental bronchus of the apicoposterior segment of the left upper lobe. Distal to the mass, a wedge-shaped small zone of air trapping was noted Figure 1 b.

View larger version (131K): [in this window] [in a new window]   Figure 1. Panel a. Somatostatin receptor scan. Static anterior view of the neck-chest area by Indium-111-pentetreotide shows pathologic tracer uptake in the parahilar area of the left upper lobe. Panel b. Chest computed tomographic scan. Coronal reconstruction shows the parahilar carcinoid with a small area of distal air trapping.

Left upper lobectomy showed a typical invasive carcinoid and metastatic foci within one lymph node. Immunocytochemical staining of specimens from both the tumor and the metastatic lymph node was positive for ACTH. The plasma ACTH concentration was 33 pmol/L in the pulmonary artery feeding the tumor and 64 pmol/L in the pulmonary vein draining the tumor.

One month after surgery, the patient showed marked clinical improvement. Without any medication, her blood pressure was 120/80 mm Hg. The morning cortisol level after 1-mg overnight dexamethasone administration was 30 nmol/L (normal, <138 nmol/L).

Discussion

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Excess ACTH is usually secreted by pituitary adenomas, which can be distinguished from the ectopic ACTH-producing tumors on the basis of their response to various suppressive and stimulatory agents. Ectopic ACTH-producing tumors commonly have their origin in the neuroendocrine system [4], and more than half are bronchial carcinoid tumors [5]. At least 30% of the bronchial carcinoid tumors eventually develop local and distant metastases [2]. Control of the metastatic potential and the endocrine activity of the tumor necessitates accurate localization, which has proved to be difficult [6]. This difficulty is especially evident in cases of small-sized central bronchial carcinoid tumors, which may easily be confused with blood vessels of the same size.

Several neuroendocrine tumors, including those secreting ACTH, have somatostatin receptors [7] and respond clinically and biochemically to administration of the long-acting somatostatin analog octreotide [8]. Nevertheless, some ACTH-secreting tumors do not have these receptors and do not respond to octreotide treatment [3, 9]. Recently, the interaction of Indium-111-pentetreotide with ACTH-secreting bronchial carcinoid has been reported in two cases. In one case, the carcinoid proved to be devoid of somatostatin receptors both on autoradiography and on scintigraphy [3]. In the second case, which has been reported only in abstract form, scintigraphic studies with Indium-111-pentetreotide showed the carcinoid [10]. It thus appears that the inconsistent detection of ACTH-secreting bronchial carcinoids depends on the degree of somatostatin-receptor expression in these tumors. This expression can be identified in vivo by a radiolabeled somatostatin analog. Our findings suggest that in cases of obscure ectopic ACTH-producing tumor, somatostatin-receptor scintigraphic study is warranted because it may localize the tumor for surgical removal or indicate which patients need octreotide treatment.

Addendum

After submission of our manuscript, a similar case was reported elsewhere [11].