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1 Department of Radiology, University of Washington, Box 354755, 4245 Roosevelt
Way NE, Seattle, WA 98105.
2 Department of Radiology, Brooke Army Medical Center, San Antonio, TX.
Received April 13, 2006;
accepted after revision April 13, 2006.
The opinions and assertions contained herein are the private views of the
authors and are not to be construed as official or as representing the views
of the Department of the Army, the Department of the Air Force, or the
Department of Defense.
Abstract
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Keywords: adrenal gland • genitourinary imaging • kidney • pheochromocytoma
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| QUESTION 1 Which one of the following radiologic features, if present, may be useful in differentiating pheochromocytoma from adrenal adenoma on abdominal CT?
QUESTION 2 Which examination is contraindicated in the workup of suspected pheochromocytoma?
QUESTION 3 Which condition is associated with pheochromocytoma?
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Solution to Question 1
Attenuation serves as the principal manner for differentiating benign
adenoma and pheochromocytoma
[1]. Pheochromocytomas may
contain intracellular fat, but only rarely do they contain sufficient lipid to
decrease attenuation to less than 10 H. Option B is the best response.
Options A, C, and D are incorrect. Although pheochromocytoma can undergo
intracellular lipid degeneration, the presence of macroscopic fat (
30 H)
is virtually diagnostic of benign myelolipoma. Increased washout is more
strongly associated with benign adenoma. With IV contrast injection, both
pheochromocytoma and adrenal adenoma show enhancement during the arterial
phase. However, pheochromocytoma typically shows washout of less than 40% with
a 15-minute delay. Calcification is a rare feature of pheochromocytoma; its
presence neither confirms nor excludes the diagnosis.
| QUESTION 4 In the evaluation of an incidentally discovered adrenal mass, which feature on MRI, if present, would virtually eliminate pheochromocytoma as a diagnostic possibility?
QUESTION 5 Which of the following incidentally discovered adrenal lesions has specific features on CT that may allow radiologic diagnosis?
QUESTION 6 Which of the following characteristics of an adrenal adenoma may reliably distinguish it from an adrenal metastasis?
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Solution to Question 2
CT-guided core biopsy should NOT be contemplated or performed when
pheochromocytoma is suspected. Manipulation of these catecholamine-secreting
tumors can precipitate life-threatening hypertension or cardiac arrhythmias
[2]. An accurate diagnosis must
be made through less invasive means. Option C is the best response. If
an adrenal mass is not visualized on CT, then MRI is a reasonable choice for a
subsequent study. Pheochromocytoma typically has low intensity on T1-weighted
images and high intensity on T2-weighted images. The 24-hour measurement of
urine VMA and metanephrine levels is an appropriate screening test for
pheochromocytoma. These tests should be considered in younger patients with
paroxysmal hypertension. For patients in whom CT and MRI do not reveal an
adrenal mass despite a high level of clinical and laboratory suspicion, PET is
a reasonable alternative. Other useful nuclear imaging studies include MIBG
and octreotide.
Solution to Question 3
Approximately 90% of pheochromocytomas are sporadic, and about 10% are
related to hereditary conditions. Multiple endocrine neoplasias (MEN-2A and
MEN-2B), von Hippel-Lindau disease, von Recklinghausen's disease or
neurofibromatosis, and Carney's triad are all associated with the occurrence
of pheochromocytomas [3].
Carney's triad consists of gastric stromal tumor, extraadrenal paraganglioma
(usually functional), and pulmonary chondroma. Carcinoid syndrome is
associated with carcinoid tumors that secrete excessive amounts of serotonin;
manifestations may include low blood pressure. Carcinoid syndrome does not
occur with pheochromocytoma. Option A is not the best response.
Osler-Weber-Rendu syndrome, or hereditary hemorrhagic telangiectasia, is a
condition in which patients may have some combination of spontaneous recurrent
nosebleeds, mucocutaneous telangiectasia, visceral involvement, and an
affected first-degree relative
[4], but this condition is not
in any way associated with pheochromocytoma. Option B is the best
response. Therefore, Option C is not the best response. Congenital adrenal
hyperplasia is a group of heritable disorders characterized by cortisol and
aldosterone deficiencies and overproduction of androgens; this condition is
not associated with pheochromocytoma. Option D is not the best response.
Autosomal polycystic kidney disease does not have adrenal manifestations.
Option E is not the best response.
Solution to Question 4
On MRI, pheochromocytomas are solid masses that generally have high signal
intensity on T2-weighted images and heterogeneous enhancement after the IV
administration of gadolinium. Unlike adrenal adenomas, there should be an
absence of lipid on chemical shift MRI
[5]. Thus, Options B, C, and D
are correct features of pheochromocytoma on MRI, and are not the best
responses. Size is not a useful criterion for distinguishing pheochromocytoma
from other adrenal masses. Option E is not the best response.
Pheochromocytomas do not have a cystic morphology. Option A is the best
response.
Solution to Question 5
Myelolipomas are benign tumors composed of bone marrow elements and
generally present incidentally on imaging of the abdomen performed for other
reasons [1]. Myelolipomas
generally contain a large amount of mature fat, allowing a confident imaging
diagnosis on CT. Myelolipomas occasionally do not contain fat, in which case
an imaging diagnosis cannot be made. Option E is the best response. CT
findings of granulomatous diseases involving the adrenals, such as
tuberculosis and histoplasmosis, are nonspecific and include soft-tissue
masses, cystic changes, calcifications, or some combination of these findings.
Adrenal hemangiomas are rare benign tumors that are seen on CT as large,
well-defined masses of soft-tissue density that exhibit inhomogeneous
enhancement after contrast injection. Ganglioneuromas are benign neural tumors
that present as solid masses and show variable enhancement with contrast
material. Approximately 10% of pheochromocytomas are clinically silent; most
of these are discovered as incidental adrenal masses with nonspecific CT
characteristics. Options A, B, C, and D are incorrect responses.
Solution to Question 6
Most adrenal adenomas are lipid-rich and can be correctly diagnosed on
chemical shift MRI [5].
Option C is the best response. The presence of lipid may also result in
adenomas being hypoattenuating relative to normal adrenal tissue on unenhanced
CT [6]. Metastases do not
contain fat. Calcification in adrenal adenomas is rare, and the presence or
absence of calcification does not reliably distinguish these from metastases.
Most lipid-poor adenomas can be accurately characterized on delayed enhanced
CT, in which there is more rapid washout of contrast material from adenomas
than from metastases. Signal intensity of adenomas on T2-weighted MRI tends to
be low but overlaps that of metastases; therefore, signal intensity alone is
not a reliable method of differentiation. Options A, B, D, and E are incorrect
responses.
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