DOI:10.2214/AJR.08.1166
AJR 2009; 192:300-301
© American Roentgen Ray Society
Radiologic-Pathologic Conferences of the University of Texas M. D.
Anderson Cancer Center |
Adrenal Pheochromocytoma with Surrounding Brown Fat Stimulation
Revathy B. Iyer1,
Charles C. Guo2 and
Nancy Perrier3
1 Division of Diagnostic Imaging, The University of Texas M. D. Anderson Cancer
Center, 1515 Holcombe Blvd., Box 57, Houston, TX 77030.
2 Division of Pathology, The University of Texas M. D. Anderson Cancer Center,
Houston, TX.
3 Division of Surgical Oncology, The University of Texas M. D. Anderson Cancer
Center, Houston, TX.
Received May 5, 2008;
accepted after revision July 17, 2008.
Address correspondence to R. B. Iyer
(riyer{at}mdanderson.org).
Keywords: adrenal gland • brown fat • FDG PET/CT • pheochromocytoma
A 62-year-old woman with a history of poorly controlled hypertension
and anxiety presented with abdominal pain and a hypertensive crisis. Abdominal
imaging revealed a 3.5-cm right adrenal mass. A 24-hour urinary collection
revealed markedly elevated catecholamines (particularly norepinephrine, which
was 774 µg/24 hr [normal, 15-100 µg/24 hr]), confirming the diagnosis of
pheochromocytoma.
Dedicated adrenal CT showed an approximately 3.5-cm enhancing mass in the
right adrenal gland with central low attenuation and significant soft-tissue
stranding in the surrounding fat. Whole-body 18F-FDG PET showed
intense uptake of the mass as well as the surrounding retroperitoneal tissues,
with a maximum standardized uptake value of approximately 20 extending into
the mediastinum (Fig. 1A). The
patient received 
- and β-blockers in preparation for surgery.
Repeat abdominal CT was performed and revealed a decrease in the previously
seen retroperitoneal stranding (Figs.
1B and
1C). The patient was taken to
the operating room and underwent a right adrenalectomy. Gross sections
revealed a 3.8-cm well-circumscribed tan-yellow tumor in the adrenal gland.
Microscopically, the tumor cells were arranged in solid or alveolar patterns
and surrounded by a capillary-rich framework
(Fig. 1D). The cytoplasm was
amphophilic with a fine granular texture, and the nuclei were round to ovoid
with a single prominent nucleolus. The surrounding adipose tissue was composed
of multivacuolated and univacuolated cells with increased vascularity. The
final pathologic diagnosis was pheochromocytoma with surrounding brown fat
(Fig. 1D).
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Fig. 1A —62-year-old woman with predominantly norepinephrine-producing
adrenal pheochromocytoma. Coronal 18F-FDG PET
maximum-intensity-projection image shows intense uptake in retroperitoneum
extending to mediastinum (arrow).
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Fig. 1B —62-year-old woman with predominantly norepinephrine-producing
adrenal pheochromocytoma. Contrast-enhanced CT scan shows right adrenal mass
(black arrow) with significant stranding in surrounding fat
(white arrow).
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Fig. 1C —62-year-old woman with predominantly norepinephrine-producing
adrenal pheochromocytoma. Unenhanced CT scan after administration of -
and β-adrenergic blockers shows significant decrease in stranding in
surrounding fat (arrow).
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Fig. 1D —62-year-old woman with predominantly norepinephrine-producing
adrenal pheochromocytoma. Photomicrograph of tumor cells shows
pheochromocytoma and surrounding brown fat. Pheochromocytoma cells are
arranged in solid patterns with amphophilic cytoplasm and round nuclei
(white arrow). Brown fat is composed of multivacuolated and
univacuolated cells with increased vascularity (black arrow). (H and
E, x100)
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Pheochromocytoma is an uncommon neoplasm that originates from chromaffin
cells and may arise in the adrenal medulla (90%) or in extraadrenal locations
(10%). Pheochromocytomas induce hypertension through the production of
catecholamines, primarily epinephrine, and, less commonly, norepinephrine.
Pheochromocytomas are typically sporadic and solitary neoplasms
[1]. Only a small percentage of
patients with hypertension have a pheochromocytoma, but in those who do,
complete resection of the functional tumor provides cure. Cross-sectional
imaging such as CT or MRI is an excellent study for showing adrenal
masses.
Brown fat is normally present in fetuses and infants and diminishes in
adults to account for only 1% of the total body mass. Brown fat may have a
metabolic or a thermoregulatory function. Remnants of brown fat in the adult
are usually found in the neck, mediastinum, axilla, retroperitoneum, and
abdominal wall [2]. Brown
adipose tissue has much more sympathetic noradrenergic innervation than white
adipose tissue [3].
Norepinephrine also has a regulatory function in brown fat. Catecholamine
stimulation increases the number of brown fat cells, stimulates lipolysis and
glucose transport, and uncouples protein-1 expression in brown fat cells,
resulting in heat production
[3].
Brown fat is frequently an incidental finding on FDG PET that may result in
false-positive findings [4].
Careful correlation with coregistered CT images should be performed to exclude
any masses in areas of brown fat uptake. After injection of the radiotracer,
as patients wait to be imaged, controlled room temperature is important to
prevent thermogenesis and increased brown fat stimulation. In patients with
adrenergic stimulation due to excess catecholamine production, brown adipose
tissue may be more abundant than in normal adults. The localization of FDG in
areas of excess brown fat in these patients likely results from increased
glucose transport related to norepinephrine excess
[3,
5].
When interpreting examinations in patients with pheochromocytoma, the
radiologist should bear in mind that FDG uptake may be increased in these
patients because of the high circulating levels of norepinephrine. The
dramatic FDG uptake in the surrounding retroperitoneal regions may make it
difficult to resolve the pheochromocytoma from the surrounding brown fat with
PET alone; PET/CT fusion is particularly helpful in this regard. In this
patient, after administration of -adrenergic and β-blockers, the
extent of hypervascularity in the retroperitoneal fat decreased. Although
follow-up PET was not performed, it is postulated that brown fat activity on
FDG PET would also have decreased, as has been shown previously
[5].
References
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imaging with (18)F-6-fluorodopamine PET/CT, (18)F-FDG PET/CT, and (123) I-MIBG
SPECT: a study of patients being evaluated for pheochromocytoma. J
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18F FDG uptake in adipose tissue and muscle: a potential source of
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Endocrinol 2006;67:14
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