Pulmonary carcinoid tumors are low-grade malignant tumors of neuroendocrine origin [
7] accounting for about 1% of all primary lung cancer [
8]. In the last 3 decades, the incidence of lung carcinoid tumors has significantly raised, probably due to increased clinical awareness and to the improved diagnostic yield of radiologic and endoscopic procedures [
9]. On CT scan peripheral carcinoid tumors usually present as a single lobulated lesion whose diameter rarely exceeds 2 cm. In some studies, 68-Gallium DOTATATE peptide PET-CT -a type of functional imaging in which a radioisotope-labeled somatostatin analog peptide binds to the somatostatin receptor found in carcinoid– has been found to improve the anatomic localization of neuroendocrine tumors [
10]. Nevertheless, the small size and the unfavorable sampling features of these lesions cause that more than 30% of carcinoid tumors require thoracotomy to be diagnosed [
6]. CT-guided needle biopsy might also be performed even though the diagnostic yield is moderately low and pneumothorax has been reported as a not infrequent complication for this procedure [
6,
9]. When carcinoids are centrally located, bronchoscopy plays a critical role in their diagnosis, as they are visible at endoscopic evaluation [
11,
12]. Generally flexible bronchoscopy is preferable; however, in patients at high risk for bleeding, rigid bronchoscopy may be indicated, both for obtaining biopsy specimens and also for performing ablation procedures [
11]. If carcinoids involve the peripheral region of the lung, diagnosis results more challenging giving the difficulty to find the right tributary distal bronchial segment, and thoracoscopic resection is often the method of choice. US-guided bronchoscopy demonstrates a high diagnostic yield with low complication rate in the diagnostic evaluation of small peripheral nodules [
6]. Tanaka et al. have recently reported a case of EBUS-diagnosed peripheral carcinoid tumor [
11]. The authors show how the use of ultrasound technique confirmed the presence of a solid nodule located where endoscopic evaluation found a yellow sub-mucosal lesion. In our case the R-EBUS technique was essential to find the correct place to sample giving the lack of appreciable endobronchial involvement at mucosal or sub-mucosal level. It is worth noticing that peripherally radial ultrasound did not help in understanding the o’clock position of a lesion in order to guide the biopsy. However, when the lesion occupies an important portion of the bronchus lumen, this limitation could be overcome by the precise identification of the right tributary bronchus and the appropriate distance from the tip of the endoscope. When forceps are pushed in the point previously identified whit the ultrasound probe, the biopsy can be confidently performed and the rate of positivity is generally high. This limitation is greater when the lesion occupies only a small portion of the distal bronchus or when needle is used instead of forceps.
In conclusion, we report a case of a peripherally located carcinoid tumor whose diagnosis was made possible only through transbronchial biopsy performed with R-EBUS. This case emphasizes how ultrasound is more than useful in the diagnostic process of lung small peripheral tumors, particularly when they present as occult at endoscopic investigation.