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Diagnostic Radiology · Diagnostic Radiology of the Abdominal Organs

PET/CT and Adrenal Scintigraphy

PET/CT and scintigraphy are molecular imaging methods that play a key role in the differential diagnosis of complex adrenal masses. They evaluate not only the structure but also the functional activity of tissues, helping to distinguish benign adenomas from malignant processes without biopsy.

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PET/CT SensitivityReaches 100% in evaluating malignant adrenal masses.
Comparison with the liverThe ratio of the lesion SUV to the liver SUV is the main criterion for differential diagnosis.
[11C]-MetomidateA specific radiopharmaceutical for the adrenal cortex (a marker of 11β-hydroxylase).
BiopsyPerformed rarely, strictly after ruling out pheochromocytoma.
3 min readFor medical studentsUpdated Sep 25, 2026
Material prepared by WhiteCoat Pro editorial team based on platform study guidesReviewed by medical editor: Aulov A. A., general practitioner · 09/24/2026

PET/CT: 18F-FDG Uptake Criteria

The differential diagnosis in 18F-fluorodeoxyglucose (18F-FDG) PET/CT is based on comparing the level of radiopharmaceutical uptake by the mass with that of the healthy liver parenchyma. For a more accurate quantitative assessment, the standardized uptake value (SUV) is used.

  • Uptake lower than in the liver (SUV < Liver SUV): A highly specific sign of a benign process (most often an adenoma). Such results make it possible to avoid invasive procedures if CT or MRI data are inconclusive.
  • Uptake equal to or higher than the liver (SUV ≥ Liver SUV): Characteristic of metastases (e.g., in lung cancer) and other malignant tumors. However, specificity in this group decreases (88–94%) due to the overlap of values between malignant and certain benign masses.

Specific Radiopharmaceuticals (RPs)

To increase diagnostic accuracy when FDG does not provide a definitive answer, specific tracers are used:

  1. [11C]-Metomidate (MTO): A marker of the 11β-hydroxylase enzyme. It selectively accumulates in the adrenal cortex tissue. It helps differentiate adrenocortical tumors (adenomas, adrenocortical carcinoma) from non-cortical lesions (pheochromocytomas, metastases), which are MTO-negative.
  2. Radioiodinated guanethidine analogues (131I-MIBG and 123I-MIBG): Used for medullary scintigraphy. They allow localization of pheochromocytoma as a focus of increased uptake.
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Adrenal Scintigraphy

Scintigraphy evaluates adrenal function. In addition to MIBG for the medulla, agents for the cortex are used:

  • Iodocholesterol analogues (e.g., 131I-6β-iodomethyl-19-norcholesterol). They accumulate in tumors of adrenocortical origin.
  • Radiolabeled metomidate (123I-MTO and 131I-MTO): Used to evaluate adrenocortical carcinoma (ACC), search for metastases, and select patients for targeted radionuclide therapy. It is also used to locate small adenomas in Conn's syndrome.

The Role of Biopsy in Diagnosis

The development of imaging techniques has significantly reduced the need for percutaneous adrenal biopsy (percutaneous adrenal biopsy).

Today, its main indication is suspected metastasis in a patient with extra-adrenal malignancy, when the results can affect the resectability of the primary tumor or inclusion in clinical trials. Crucial rule: pheochromocytoma must be reliably ruled out prior to the procedure to avoid triggering an adrenal crisis.

Briefly: answers to topical questions

What complications can occur during a biopsy of a pheochromocytoma without prior preparation?

Sources indicate that core-needle biopsy is potentially dangerous in pheochromocytoma; risks include the likelihood of needle-tract seeding. The specific consequences of lacking prior preparation are not detailed.

Class and exam questions

How to distinguish an adenoma from a metastasis on FDG PET/CT?

Adenomas typically show lower FDG uptake than the liver parenchyma. Metastases demonstrate a level of uptake equal to or exceeding that of the liver.

What is the value of [11C]-metomidate?

This agent is specific to the adrenal cortex. It accumulates in adenomas and adrenocortical carcinoma, but does not accumulate in metastases and pheochromocytomas.

What is the main rule before performing an adrenal biopsy?

It is strictly necessary to biochemically rule out pheochromocytoma to prevent the procedure from causing a life-threatening adrenal crisis.

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What else to study on this topic

  • Non-contrast Adrenal CT: Hounsfield Unit (HU) Criteria for Benign Masses
  • Chemical-shift MRI in the Diagnosis of Adenomas
  • Adrenal Cysts: Imaging Findings and Management
  • Myelolipoma: CT and MRI Characteristics (Detection of Macroscopic Fat)
  • Pheochromocytoma: Diagnostic Features and Imaging Findings

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Other topics in the section "Diagnostic Radiology of the Abdominal Organs"

Radiation Anatomy of the AdrenalsAdrenal IncidentalomaAdrenal Cysts and MyelolipomasAdrenocortical CarcinomaDiagnostic Imaging of Hormone-Secreting Adrenocortical TumorsPheochromocytomaAddison's Disease and Adrenal Hypofunction
Entire section "Diagnostic Radiology of the Abdominal Organs"

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