Diagnostic Anatomic Imaging for Neuroendocrine Neoplasms: Maximizing Strengths and Mitigating Weaknesses

Abstract

Neuroendocrine neoplasms are a heterogeneous group of gastrointestinal and lung tumors. Their diverse clinical manifestations, variable locations, and heterogeneity present notable diagnostic challenges. This article delves into the imaging modalities vital for their detection and characterization. Computed tomography is essential for initial assessment and staging. At the same time, magnetic resonance imaging (MRI) is particularly adept for liver, pancreatic, osseous, and rectal imaging, offering superior soft tissue contrast. The article also highlights the limitations of these imaging techniques, such as MRI's inability to effectively evaluate the cortical bone and the questioned cost-effectiveness of computed tomography and MRI for detecting specific gastric lesions. By emphasizing the strengths and weaknesses of these imaging techniques, the review offers insights into optimizing their utilization for improved diagnosis, staging, and therapeutic management of neuroendocrine neoplasms.

FIGURE 1.

Axial non-CE T1w fat-saturated (A), arterial phase T1w fat-saturated (B), and T2w SSFSE fat-saturated images. On non-CE T1w fat-saturated images (A), NETs (arrow) tend to be hypointense, compared to a healthy pancreas. In arterial phase imaging (B), they usually enhance more avidly than normal background parenchyma. They also present hyperintense on T2w imaging (C).

FIGURE 2.

Axial T2w fat-saturated SSFSE (A), T1w arterial phase (B), and EUS (C and D) images. A 6-mm pancreatic tail grade 2 NET (arrow), given its high T2w signal intensity (A), is easily detected; lesion enhancement (B) rules out cystic entities. EUS, due to its superior resolution, better visualizes the NET, which presents as a well-circumscribed hypoechoic lesion (C) and also allows for definitive diagnosis through tissue sampling (arrowhead) (D).

FIGURE 3.

Axial T1w portal venous phase (A) and coronal T2w SSFSE (B) images. A cystic lesion (arrow) in the pancreatic tail demonstrates a thick, smooth, and uniform rind of peripheral enhancement (A). There are no internal septa nor communication with the pancreatic duct (B). These features favor a cystic pancreatic NET, as subsequently confirmed by tissue sampling.

FIGURE 4.

Coronal T2w SSFSE (A) and MRCP (B) images. Cystic lesion in the pancreatic head communicates with the pancreatic duct (arrow). Duct communication excludes a cystic NET and is diagnostic of the pancreas’s side branch intraductal papillary mucinous neoplasm.

FIGURE 5.

Axial T1w portal venous phase (A) and coronal T2w SSFSE (B) images. A cystic lesion (arrow) in the pancreatic body demonstrates a thick rind of peripheral enhancement and does not communicate with the pancreatic duct. However, this cystic lesion presents a lobulated contour and contains enhancing internal septa; these features are more in favor of other etiologies, including mucinous cystic neoplasm, as subsequently pathologically confirmed, rather than of NETs.

FIGURE 6.

Coronal arterial phase CE-CT (A), fused DOTATE PET/CT (B), and coronal DOTATATE PET (C). Primary cystic pancreatic NET (arrowhead) demonstrates marked DOTATATE uptake in its walls. A focal hepatic lesion (arrow) displays marked arterial enhancement and radiotracer avidity, as per NET metastasis.

FIGURE 7.

Axial T1w arterial phase (A) and coronal MRCP (B) images. Despite even severe biliary duct dilation (black arrow), diagnosis of ampullary NETs (arrow) might be challenging, especially if of small size. However, arterial phase imaging can facilitate detection.

FIGURE 8.

Coronal CE-CT (A and B). Small bowel NETs (arrow) tend to occur in the last 100 cm of the distal ileum and present as focal wall thickening. Bowel distention with oral contrast facilitates detection. Associated mesenteric lymphadenopathy and desmoplastic reaction (arrowhead) tend to occur close to the primary tumor, can harbor calcifications, and can tether bowel loops.

FIGURE 9.

CT-enterography with (A) and without (B) intravenous contrast. Distal ileum is distended by fluid and contains a large and markedly enhancing polypoid NEN (arrow). The lesion, which immediately stands out after contrast injection, would be extremely hard to diagnose on non-CE CT image (B). Usage of oral and intravenous contrast facilitates detection of SB-NENs.

FIGURE 10.

Coronal T1w fat-saturated (A), T2w SSFSE fat-saturated (B), and T1w fat-saturated CE (C) images. In MRI, similarly to CT, usage of oral and intravenous contrast helps detection of NENs (arrows). These tumors would be very challenging to appreciate in the case of collapsed bowel loops and absence of intravenous contrast.

FIGURE 11.

Coronal CT image. Multiple bilateral pulmonary nodules (arrows) and mosaic attenuation. Wedge resection of the left upper and lower lobes demonstrates carcinoid tumors and tumorlets, and neuroendocrine cell hyperplasia within airway epithelium in keeping with DIPNECH.

FIGURE 12.

Axial CT (A) and DOTATATE PET (B) images. There is an endobronchial nodule in the bronchus intermedius (arrow), which demonstrates marked DOTATATE PET uptake (arrow). This was confirmed to be a typical carcinoid on resection.

FIGURE 13.

Axial CT (A) and FDG PET (B) were imaged. There is a dominant nodule in the right middle lobe (arrow) and subcarinal adenopathy (arrowhead), which, along with another right lung nodule (white short arrow), demonstrates marked FDG activity. This was confirmed to be an atypical carcinoid on biopsy.

FIGURE 14.

Monochromatic (A) and nonmonochromatic (B) CE-CT images. Monochromatic images increase the conspicuity of contrast enhancement among anatomic structures and tissues, facilitating the detection of hypervascular NEN metastases (arrows) to the liver, which could have otherwise blended with similar attenuation background hepatic parenchyma as in B.

FIGURE 15.

Sagittal CT (A) and STIR (B) images. NEN metastases to the bones (arrow) tend to present sclerotic as in A. MRI outperforms CT in detecting additional early metastases (arrowhead), which otherwise could be completely undetected on CT.