Carcinoid



Carcinoid


Todd M. Blodgett, MD

Alex Ryan, MD

Omar Almusa, MD





Key Facts


Terminology



  • Neuroendocrine tumor derived from enterochromaffin cells


  • Carcinoid, carcinoid syndrome (CS), carcinoid tumor


Imaging Findings



  • Primary bowel lesion with spiculated soft tissue mass in abdomen ± desmoplastic reaction ± calcifications


  • Hepatic or lung tumors in patient with CS


  • Chest mass: Endobronchial lesion with or without post-obstructive pneumonia


  • FDG PET: Sensitivity 75%



    • Generally low FDG uptake among neuroendocrine tumors


  • Atypical carcinoid can appear as a small pulmonary nodule with extensive hilar or mediastinal lymph node enlargement


  • Carcinoids tend to be vascular and can exhibit considerable enhancement



    • Helpful for differentiating tumor from obstructive atelectasis and adjacent mucous plugs


  • Whole-body morphologic imaging and somatostatin receptor scintigraphy best combination


Top Differential Diagnoses



  • Lymphoma


  • Other Neuroendocrine Tumors


  • Mesenteritis


  • Liver Metastases


Diagnostic Checklist



  • FDG PET or PET/CT may show only mild to moderate FDG activity within lesions






Axial CECT shows a slightly spiculated mass in the small bowel mesentery with areas of calcifications image, most compatible with carcinoid.






Axial fused PET/CT shows moderate FDG activity in the mesenteric mass image, compatible with carcinoid.


TERMINOLOGY


Abbreviations and Synonyms



  • Carcinoid, carcinoid syndrome (CS), carcinoid tumor



    • May indicate malignant or benign disease


Definitions



  • Neuroendocrine tumors arising from enterochromaffin cells of Kulchitsky


IMAGING FINDINGS


General Features



  • Best diagnostic clue



    • Variably calcified soft tissue mass in abdomen with spiculation and desmoplastic reaction



      • Often asymptomatic


    • Tumors of liver or lung in patients with carcinoid syndrome


    • Mass within bronchus with varying degrees of post-obstructive pneumonia


  • Location



    • Abdominal carcinoid common, specifically in large intestine and appendix



      • Primary carcinoids of bowel are often not seen with CT


      • Metastases are frequent from midgut tumor but rare from appendiceal primary


    • Thoracic carcinoid most commonly found within bronchial lumen



      • Also seen in lung parenchyma and peribronchiolar lymph nodes


      • Peripheral lung tumor may represent atypical pulmonary carcinoid, half of which show lymph node involvement or distant metastases


  • Size



    • May become bulky, up to 25 cm


    • Size generally correlates with malignant behavior



      • Tumors < 1 cm metastasize in 2% of cases


      • Tumors 1-2 cm in 50% of cases


      • Tumors > 2 cm in 85% of cases


    • Volume may not change following treatment despite good clinical response


  • Morphology



    • Thoracic carcinoid highly vascular with no characteristic calcification distribution




      • Atypical carcinoid: Small peripheral nodule surrounded by extensive hilar/mediastinal lymphadenopathy


    • Abdominal carcinoid typically manifests as homogeneous mesenteric mass with spiculation and variable calcification



      • Primary bowel lesion often not identified


      • Thickened neurovascular bundles may present as stellate or curvilinear fibrosis radiating from lesion and distorting surrounding bowel


Imaging Recommendations



  • Best imaging tool



    • Whole-body morphologic imaging and somatostatin receptor scintigraphy


    • SUV on FDG PET generally correlates with aggressiveness of tumor


  • Protocol advice



    • Somatostatin receptor imaging (SRI)



      • Administer 6 mCi (222 MBq) In-111 pentetreotide IV


      • Image with 173 keV and 247 keV photopeaks of In-111


      • Administer mild bowel cathartic to decrease colon accumulation in patients not experiencing diarrhea


      • Urinary bladder should be emptied prior to imaging to avoid obscuring pelvic findings


CT Findings



  • General



    • CT has shown superiority to octreotide scan for characterization of primary tumor and liver metastases


    • Benign and malignant disease cannot reliably be differentiated with CT



      • Half of indeterminate lesions are benign on biopsy


    • Carcinoid tumor highly vascular



      • Distinguishable from obstructive atelectasis and mucous plugs on contrast-enhanced images


  • Chest



    • Small pulmonary nodule with extensive hilar/mediastinal lymphadenopathy is classic finding for atypical carcinoid


    • Central carcinoids more commonly have variable calcification (˜ 1/3 of cases)



      • No pathognomonic pattern of calcium distribution known


      • Less commonly seen in peripheral tumors


  • CECT



    • Typical carcinoid



      • Homogeneous, smooth-bordered lesion


      • Highly vascular tumor with intense contrast enhancement


    • Atypical carcinoid



      • Generally larger tumors


      • May show central necrosis and be associated with hilar lymphadenopathy


  • Abdomen



    • Submucosal lesions



      • Vascular lesions enhance intensely


      • Mural nodules more clearly visualized with water contrast


      • Well-defined morphology


    • Small bowel carcinoid



      • Masses are soft-tissue attenuation of variable size


      • Radiating stranding and border spiculation common


      • Retractile mesenteritis and treated lymphoma may share appearance, with calcification and desmoplastic reaction


      • Bowel loop ischemia may present as wall thickening and submucosal edema


    • Extension to mesentery



      • Homogeneous or heterogeneous ill-defined mass with spiculations and variable calcification


      • Desmoplastic reaction presents with finger-like extension into adjacent mesentery


      • Variable encasement and narrowing of mesenteric vessels


      • Fibrosis and desmoplastic reaction leads to fixation and obstruction of small bowel


      • Some tumors demonstrate cystic density



    • Metastasis to liver



      • Hypoattenuating on NECT


      • Strongly enhancing on CECT


      • Delayed images may show lesion isodense to liver


      • Often multiple


    • Colonic extension



      • Extraluminal mass common and better delineated on CT


      • Colon carcinoid has similar CT findings to adenocarcinoma, including a discrete mass or focal wall thickening


Nuclear Medicine Findings

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Sep 22, 2016 | Posted by in MAGNETIC RESONANCE IMAGING | Comments Off on Carcinoid

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