How is the diagnosis made?
Diagnosis of pulmonary carcinoids is suspected when the symptoms above are noted, or based upon x-ray or CT findings. Blood tests or a biopsy may be done next depending upon symptoms and the appearance of the x-rays. Hormones or tumor markers typically associated with carcinoid tumors will usually be checked in the blood (5HT or serotonin) and in the Urine (5HIAA). Chromogranin A is usually measured as well. It is not associated with symptoms but is frequently elevated in a variety of neuroendocrine tumors. If an elevated level drops after the tumor is resected, it is useful to follow the level to look for evidence of recurrence after surgery. Some Carcinoid tumors make hormones that can produce the carcinoid syndrome, Cushing's syndrome or Acromegaly. The presence of carcinoid syndrome is more common when there is already spread to the liver present. Carcinoid syndrome only occurs in 1-2% of patients at the time of initial diagnosis. When the tumor produces ACTH it can stimulate the adrenal glands to produce steroids causing Cushing's syndrome. This only happens 5% of the time. Acromegaly or gigantism occurs when Growth hormone releasing hormone (GHRH) or Growth hormone (GH) is produced by the tumor. Tiny carcinoid tumors can produce enough hormone to cause very significant problems. Fortunately, these biochemical changes will usually resolve if the tumor has not spread and can be completely removed. The diagnosis can often be made by bronchoscopy; a narrow flexible scope is used to examine the lining of the airways. Cells from the tumor can be obtained by brushing or biopsy during the same procedure. Tumors farther from the trachea can often be biopsied with a needle under CT guidance. Special stains used by the pathologist can show the chromogranin A content confirming that these are carcinoid tumor cells.
Figure 4: CXR showing lobulated carcinoid mass in right lung
Figure 5: CT scan showing compressed lung or atelectasis beyond obstruction from bronchial carcinoid
The plain chest x-ray (CXR) may reveal atelectasis or collapse of a segment of the lung beyond an obstructing carcinoid. When these tumors become larger they may be visible as smooth ovoid or slightly lobulated masses. (Figure 4) Locating and defining the extent of the tumor is often possible with a high resolution or fine cut CT scan. If the mass is not visible but there is collapse of a portion of the lung (Figure 5), this can direct the radiologist, pulmonologist or surgeon where to look for the tumor that is producing a blockage to the lung. MRI is used less often. PET scans can be used as well to look for tissue with a high metabolism such as a cancer or carcinoid tumor. Unfortunately, infectious and inflammatory conditions can also cause increased activity and this may be confusing if the tumor has caused pneumonia and lymph nodes that are reactive to the infection may be misinterpreted as showing evidence of metastasis. The PET scan, on the other hand, may identify sites of spread in advanced disease that were not suspected. Fortunately spread to lymph nodes occurs in only 10 - 15 % of the cases of typical pulmonary carcinoids.
Most carcinoid tumors have a receptor on the surface that binds to somatostatin, a hormone that regulates growth and secretion of neuroendocrine cells. Octreotide or pentreotide are variations of this hormone that can be labeled for nuclear medicine scans (octreoscan or somatostatin SPECT) and combined with CT scans are able to localize carcinoid tumors very precisely. Metastases with functioning receptors may also be identified with an octreoscan, and occult or hidden tumors may be localized with hand held Geiger counter in the operating room in some cases.