CT imaging in the hunt for ectopic ACTH tumors

Once the biochemical evidence of excess ACTH production leads to the diagnosis of Cushing's Syndrome for a patient, the next step is determining the source of excess ACTH production. Usually the source for the excess ACTH is a tumor on the pituitary gland. However, ectopic sources may also be ACTH secreting tumors.

Eighty to 85% of Cushing’s syndrome is ACTH-dependent, of which 80–90% will be due to a pituitary adenoma—Cushing’s disease (CD) [1]. Ten to 15% will have a nonpituitary source, referred to as ectopic ACTH secretion (EAS) [2], of which 80% have an identified source within the chest and abdomen whilst 20% have no detected source and are referred to as occult [1].

This article talks about the use of computed tomography (CT) to locate the source of the EAS. According to the authors, a bilateral inferior petrosal venous sampling (BIPPS) is the first step in determining whether the source of excess ACTH is ectopic, with a 95% sensitivity. They say "false positives are extremely rare (<1%)> and there is a false negative rate of 2–4%".

The authors include information about imaging multiple tumors including the following:

Bronchial carcinoids

Thymic carcinoids

Gastrointestinal carcinoids

Pancreatic neuroendocrine tumours

Medullary thyroid carcinomas

Phaeochromocytomas

They also mention other tumors briefly:

Many tumours have been reported in the literature to result in EAS such asovarian carcinoid, ovarian adenocarcinoma, ovarian androblastoma, ovarian teratoma, ovarian Sertoli cell carcinoma, ovarian dermoid cyst, prostatic adenocarcinoma, prostatic small cell carcinoma, small cell carcinoma of the uterine cervix and olfactory neuroblastoma [6].

The authors recommend the use of ¹¹¹In-octreotide in some cases and mention the enlargement of the adrenals, as well as shape and hyperplasia depending on the type of EAS. They conclude that CT imaging can lead to earlier diagnosis and treatment of these excess ACTH sources.

(Picture is from the article)

Paul A. Sookur, Anju Sahdev, Andrea G. Rockall, Andrea M. Isidori, John P. Monson, Ashley B. Grossman, Rodney H. Reznek (2009). Imaging in covert ectopic ACTH secretion: a CT pictorial review European Radiology DOI: 10.1007/s00330-008-1274-5