Page 3 - Management of the incidentally discovered adrenal mass

incidentally discovered adrenal mass

asymptomatic, however it remains up to the astute clinician a previous oncologic history, as metabolically-active lesions
to adequately evaluate each patient for the subtle clinical typically have increased uptake of FDG versus benign
signs of adrenal hyperfunction or malignancy. The signs lesions. 11
and symptoms of overt Cushing’s syndrome, pheochromocy- Adrenal scintigraphy is effective at characterizing the pat-
toma, primary aldosteronism and adrenocortical carcinoma tern of hyperfunctioning lesions, unilateral versus bilateral
are well-described in the literature. 1,8 uptake, but it is not typically used in the initial workup of
AIs. 15,16 Metaiodobenzylguanidine (MIBG) scintiscan can be
Radiologic evaluation useful in assessing patients with suspected pheochromo-
cytoma.
Advances in modern imaging have made it a powerful ally
in delineating benign from malignant processes in AIs. The Fine-needle biopsy
most common imaging modality employed to evaluate AIs is
CT. With current collimation, masses between 3 and 9 mm Fine-needle aspiration biopsy (FNB) is currently not rec-
are being discovered on a routine basis, which emphasizes ommended for the routine workup of AI. Its findings rarely
that this issue will only increase in the future. As previ - alter treatment, except in patients with potential metasta-
ously mentioned, myelolipoma, cysts and hemorrhages have ses or infectious processes. Often, clinical, hormonal and
17
distinct features on imaging that are well-documented in radiologic findings can effectively direct treatment. It is also
the literature. Characteristics of pheochromocytoma and associated with relatively rare, but significant, complica-
11
malignant processes include size (>3 cm), attenuation of tions; pheochromocytoma must always be ruled out before
>10 HU on unenhanced CT, heterogenous texture and biopsy is undertaken to avoid potentially life-threatening
increased vascularity with decreased contrast washout at hemorrhage and hypertensive crisis. 18
10 to 15 minutes. 8,12 Adenomas typically contain a greater
proportion of intracellular fat in comparison to malignant Hormonal evaluation
incidentalomas. Therefore, in CT densitometry, a cut-off of
<10 HU of a region of interest over a mass increases the The preferred method of hormonal evaluation remains an
likelihood of adenoma, sensitivity and specificity by 71% area of constant debate. The literature supports that the over-
and 98%, respectively. Unfortunately, lipid-poor adeno- night 1 mg dexamethasone suppression test (DST), sensitiv-
11
mas represent up to 30% of all adenomas and may be indis- ity and specificity 73% to 100% and 90%, respectively,
tinguishable from malignancy on unenhanced CT. 13 appears to be the test of choice to rule out autonomous
Chemical shift magnetic resonance imaging (CSI), like glucocorticoid production, Cushing’s syndrome or subclini-
unenhanced CT, uses the lipid-rich property of most aden- cal Cushing’s syndrome (sCS). Some authors advocate the
6
omas to differentiate benign from malignant. Its main utility use of higher dose DST (2, 3 or 8 mg) to decrease the risk of
is seen in evaluating dropout in out-of-phase versus in-phase false positives. 19-21 The ultimate cut-off value for sCS remains
images, as well as in evaluating indeterminate heterogen- to be elucidated, but cut-offs from 50 nmol/L to 138 nmol/L
eous density lesions suspected to have microscopic or have been used to define adrenal autonomy with a lower
macroscopic fat (myelolipomas). Similar to unenhanced CT, cut-off increasing the risk of false positives. 4,8,9 Consideration
overlap between benign and malignant processes occurs can be given to using the 24-hour urinary-free cortisol (UFC)
in 10% to 30% of cases. 13,14 Therefore, if an AI is indeter- for screening with the low dose DST used to differentiate
minate on unenhanced CT, CSI may not provide additional Cushing’s from sCS if the cortisol level on the 24-hour test
information and should be deferred in favour of contrast CT is elevated. The UFC should be performed with the under-
with washouts. standing that a subset of patients with Cushing’s syndrome
If unenhanced CT or CSI is indeterminate, contrast may have normal results. 8,22
enhanced CT with washouts at 10 to 15 minutes has Pheochromocytoma is best assessed by 24-hour urin-
been shown to have excellent sensitivity and specificity, ary metanephrines and/or catecholamines, sensitivity and
approaching 100%, in differentiating between adenomas specificity 95% and 95%. A more recent addition to the
6
and nonadenomatous incidentalomas. 11,14 With such high screening arsenal are fractionated plasma metanephrines,
efficacy, delayed contrast CT may make CSI and the positron which may be a more sensitive test (98%), but sacrifices
emission tomography scan unnecessary except in specific specificity (89%). 23,24 As such, its use should be reserved
situations, especially if costs and resource allocation are for confirmatory testing as opposed to primary screening.
taken into consideration. However, this potential benefit Plasma metanephrine testing may not be widely available
needs to be weighed against the risk of increasing radiation outside select centres, therefore 24-hour urinary metaneph-
exposure to the patient. rines is suggested for initial screening.
2-[18F]fluoro-2-deoxyglucose (FDG) positron emission Hypertensive patients with adrenal incidentalomas should
scan can be useful in detecting metastasis in patients with be assessed for hyperaldosteronism (HA). Traditionally, HA

CUAJ • August 2011 • Volume 5, Issue 4 243