Computed tomography semiotics
The appearance of carcinoid tumors on tomograms is largely determined by their location relative to the bronchial tree and vascular structures.
- Central location: the tumor can partially obstruct the lumen of large bronchi (e.g., left main bronchus). In some cases, especially when analyzing scans in the lung window, the only sign of a centrally located tumor may be a narrow strip of atelectasis (often observed in the middle lobe). Clearly demarcated perihilar masses anterior to the artery supplying the right lower lobe are also found.
- Peripheral location: a small tumor in the peripheral regions appears as a typical solitary pulmonary nodule (solitary pulmonary nodule) and is radiologically indistinguishable from masses of other etiologies.
Standard chest CT protocol
High-quality imaging requires strict adherence to scanning and positioning parameters. The patient is placed in the supine position (supine position) with arms raised overhead.
- Scout projection: performed in anteroposterior (AP) and, optionally, lateral views. This is necessary for precise planning of scan zones and reducing radiation dose.
- Contrast administration: for clear visualization of central pulmonary vessels, the optimal scanning window is 20–30 seconds. If the study is combined with abdominal and pelvic assessment, scanning is performed in the portal venous phase (portal venous phase) at 65 seconds.
- Data acquisition technique: the classical approach involves two short breath-holds (breath-holds) and two scan zones with a slight overlap in the basal regions. On modern high-speed scanners, a single volumetric acquisition (single volumetric acquisition) is possible, capturing both the arterial and portal venous phases simultaneously.
- Post-processing: generating isotropic voxels (isotropic voxels) enables routine multiplanar reconstructions (multiplanar reformatting).
Features of PET/CT and MRI
Positron emission tomography (PET/CT) The study usually covers an extensive area from the skull base (skull base) to the upper third of the thigh. Since PET data acquisition takes a long time (requiring 5–7 bed positions, up to 5 minutes each, with a total time of up to 35 minutes on older scanners), motion artifacts become an issue. For ideal spatial co-registration (co-registration) with PET data, the CT component is performed during gentle respiration (gentle respiration). If a diagnostic CT has already been performed, the CT part of the PET/CT is acquired unenhanced and low-dose (low dose).
Magnetic resonance imaging (MRI) Chest MRI is not a routine screening method for carcinoid, but it serves as a powerful problem-solving tool (problem-solving tool). In staging, it is indispensable for:
- Evaluating superior sulcus tumors (Pancoast tumors).
- Detecting invasion into the chest wall (chest wall) or other intrathoracic structures.
- Checking the structural integrity of the diaphragm (integrity of the diaphragm).
Briefly: answers to topical questions
What are the histological subtypes of lung carcinoid tumors and their differential diagnostic criteria?
Histologically, typical and atypical carcinoids, as well as poorly differentiated carcinomas, are distinguished.
- Typical carcinoids (low-grade) — account for 85–90%, more frequently located in the central airways.
- Atypical carcinoids — account for 10–15%, more frequently arise in the periphery of the lung, tend to invade and metastasize, and have a poorer prognosis.
- Large cell and small cell carcinomas (high-grade) — high-grade malignant tumors.
PET with specific radioligands is used for differential diagnosis:
| Tumor type | 68Ga-DOTATATE uptake | 18F-FDG uptake |
|---|---|---|
| Typical bronchial carcinoids | High and selective | Low |
| Poorly differentiated tumors (high-grade) | Low | High (FDG-avid) |
What are the treatment methods for lung carcinoid depending on the stage?
Surgery is the primary treatment for lung carcinoid tumors, and medical therapy is also used. Sources do not provide a direct description of stage-specific tactics, but the following approaches are distinguished:
- Organ-sparing radical surgery — priority scope (lobectomy, bilobectomy with reconstruction, or isolated radical resection with preservation of lung function).
- Endoscopic resection — used when there is no transmural bronchial wall invasion or radical resection is not feasible.
- Targeted therapy — Pazopanib (Pazopanib) at a dose of 800 mg/day is indicated for lung carcinoids (NET G1-G2).
- Combination therapy — targeted drugs can be used in combination with prolonged-release somatostatin analogs.
Class and exam questions
How can a central carcinoid manifest when analyzed in the lung window?
In some cases, the only manifestation of a central carcinoid in the lung window is a small strip of atelectasis, for example, in the middle lobe.
Why is scanning performed during gentle respiration in PET/CT?
Gentle respiration (gentle respiration) during low-dose CT is necessary for correct spatial co-registration of data with PET images, the acquisition of which takes a long time.
In which cases is it advisable to order MRI for the staging of lung tumors?
MRI is prescribed to evaluate superior sulcus (Pancoast) tumors, as well as to detail tumor invasion into the chest wall, diaphragm, or other thoracic structures.
What else to study on this topic
- Radiological patterns of partial left main bronchus obstruction
- Differential diagnosis of a solitary pulmonary nodule
- Single volumetric acquisition: physical principles
- Multiplanar reconstruction based on isotropic voxels
- Spatial co-registration in PET/CT diagnostics
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