CT and MRI in the diagnosis of pheochromocytomas
Both methods demonstrate high sensitivity and specificity in searching for pheochromocytomas. Contrast-enhanced CT detects adrenal masses with up to 100% accuracy. Historically, it was believed that contrast could provoke a hypertensive crisis; however, the procedure is now frequently performed without prior $\alpha$-blockade.
MRI offers excellent tissue contrast and is particularly useful for follow-up, surgical planning, and evaluation of complex anatomical areas (e.g., near the spinal cord or major vessels).
- On T1-weighted images (T1WI), most pheochromocytomas are iso- or hypointense relative to the liver. A high T1 signal indicates hemorrhage, which occurs in approximately 20% of cases.
- On T2-weighted images (T2WI), the typical pattern is very high signal intensity. Large tumors are often heterogeneous due to necrosis, calcifications, or hemorrhage. However, up to 35% of lesions may have only moderately high signal.
- Using chemical shift imaging (CSI), signal loss in out-of-phase does not occur.
- Administration of gadolinium rarely helps differentiate pheochromocytoma from necrotic metastases, as both pathologies avidly enhance with contrast.
Radionuclide diagnostics (MIBG and PET/CT)
Meta-iodobenzylguanidine (MIBG) scintigraphy, a norepinephrine analogue, allows visualization of chromaffin tissues throughout the body. The radiopharmaceutical is taken up by tumor cells, making it possible to detect primary nodes and metastases. The method has a sensitivity of 87–90% and a specificity of over 90%.
PET/CT is used in specialized centers. The most reliable radiopharmaceutical is considered to be 6-[18F]-fluorodopamine. Conventional 18FDG PET has low sensitivity (about 70%) and is not recommended as a first-line method, but may be useful in metastatic disease.
Extra-adrenal paragangliomas
Chromaffin tissue tumors can be located outside the adrenal glands. Multiple lesions are frequently found in a single patient.
Common locations for ectopic paragangliomas:
- Para-aortic region at the level of the renal hila (46%), including the organ of Zuckerkandl (29%).
- Thoracic paraspinal region (10%).
- Urinary bladder (10%).
- Head and neck (2–4%), predominantly carotid body tumors or vagal paragangliomas.
MRI is preferred for detecting extra-adrenal paragangliomas. On T2WI, the contrast between the hyperintense tumor and the dark blood flow in adjacent vessels is clearly visible.
Briefly: answers to topical questions
How to differentiate an adrenal adenoma from a pheochromocytoma based on unenhanced CT density values?
Differentiating these lesions solely based on unenhanced CT density is challenging, as pheochromocytomas can mimic adenomas.
| Sign | Adrenal adenoma | Pheochromocytoma |
|---|---|---|
| Unenhanced CT density | Typically $\le$ 10 HU (lipid-rich) | From 1.8 to 42 HU |
| Contrast washout profile | Absolute $\ge$ 60%, relative $\ge$ 40% | Similar to adenomas (absolute 40–89%, relative 16–83%) |
If there is any doubt, pheochromocytoma must be ruled out using clinical methods.
In the context of which hereditary syndromes is pheochromocytoma frequently encountered?
Pheochromocytoma is mentioned as part of or associated with the following conditions:
- MEN2A — includes medullary thyroid carcinoma, pheochromocytoma, and hyperparathyroidism.
- MEN2B — includes pheochromocytoma; marfanoid habitus and multiple ganglioneuromas are also described.
- Neurofibromatosis type 1 (NF-1) — pheochromocytoma is classified among non-CNS neoplasms in NF-1.
- Succinate dehydrogenase (SDH) deficiency — SDH-associated pheochromocytoma has been described.
What are the risks and contraindications for iodine-based contrast administration during CT in patients with pheochromocytoma?
Historically, contrast administration in pheochromocytoma could provoke a crisis. The source also mentions the possibility of contrast-enhanced CT without $\alpha$-blockers. Other specific risks or absolute contraindications to contrast administration in pheochromocytoma are not described in the presented materials.
Class and exam questions
Why might there be a high signal on T1WI in pheochromocytoma?
High signal intensity on T1WI indicates the presence of hemorrhage within the tumor structure, which is observed in approximately 20% of cases.
What is the main advantage of MIBG scintigraphy?
This is a whole-body scan with high specificity (>90%) that simultaneously detects adrenal tumors, extra-adrenal paragangliomas, and metastases.
Does intravenous contrast enhancement on MRI help differentiate pheochromocytoma from adrenal metastases?
No, gadolinium is rarely useful for differential diagnosis because both pheochromocytomas and metastases intensely accumulate the contrast agent.
What else to study on this topic
- Adrenal medullary hyperplasia (AMH)
- Radiology of neuroblastomas and ganglioneuroblastomas
- Specific syndromes associated with pheochromocytoma
- Differential diagnosis of adrenal hypofunction (Addison's disease)
Master the entire topic in the "Diagnostic Radiology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Pheochromocytoma" and 2,199 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 10 video lessons on the subject
Other topics in the section "Diagnostic Radiology of the Abdominal Organs"
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.