Adrenal oncocytic neoplasm is a rare adrenocortical tumor composed of oncocytic cells with abundant eosinophilic granular cytoplasm rich in mitochondria. It comprises less than 5% of all adrenocortical tumors. The biological behavior spectrum ranges from benign to malignant: oncocytoma (benign, ~80%), borderline/uncertain malignant potential (~10%), and oncocytic carcinoma (~10%). Lin-Weiss-Bisceglia criteria are used for malignancy assessment. It usually presents as large (mean 8-10 cm), well-circumscribed, solid-cystic masses. Most cases are non-functional and detected as adrenal incidentalomas. There is a slight female predominance, with a mean age at diagnosis of 40-50 years. Preoperative definitive differentiation from lipid-poor adenoma, pheochromocytoma, or adrenocortical carcinoma is difficult on imaging; final diagnosis requires histopathological examination. Treatment is surgical resection based on size and suspicion of malignancy.
Age Range
30-70
Peak Age
50
Gender
Female predominant
Prevalence
Rare
Adrenal oncocytic neoplasm develops from oncocytic metaplasia of adrenal cortex cells. The basis of oncocytic transformation is mitochondrial dysfunction and compensatory mitochondrial proliferation — the number of defective mitochondria within the cell increases dramatically, occupying the majority of the cytoplasm. This mitochondrial accumulation causes the intensely eosinophilic granular cytoplasm appearance (oncocytic cell) in histology; on electron microscopy, 60-70% of cells are filled with mitochondria. Due to dense mitochondrial content, these cells show increased metabolic activity; however, mitochondria are generally functionally defective with decreased oxidative phosphorylation capacity. On imaging, the heterogeneous enhancement of oncocytic tumors reflects variable vascularity, hemorrhage, and degeneration within the tumor. Large size (>6 cm in 70%) results not from rapid proliferation but from slow continuous growth leading to late diagnosis. High pre-contrast density on CT (>20 HU) results from intracellular lipid paucity (mitochondria occupy lipid storage space) — therefore it does not show the characteristic <10 HU density of lipid-rich adenoma. On MRI, T2 signal is variable but frequently heterogeneously hypointense to isointense because dense mitochondrial protein content shortens T2 relaxation; cystic/necrotic areas appear as T2 hyperintense foci.
Hormonally inactive, large (>6 cm), well-circumscribed, solid-cystic heterogeneous adrenal mass with high pre-contrast density (>20 HU), marked heterogeneous enhancement, and no signal drop on chemical shift — this combination is suggestive of oncocytic neoplasm; however, definitive diagnosis requires histopathological examination.
Well-circumscribed, usually >6 cm, heterogeneous density adrenal mass on non-contrast CT. Pre-contrast density values are >20 HU, inconsistent with lipid-rich adenoma (<10 HU). The mass contains high-density areas from hemorrhage and low-density areas from necrosis/cystic degeneration. Coarse calcification is present in approximately 20-30% of cases. A well-defined capsule or pseudocapsule is frequently present.
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Well-circumscribed, heterogeneous density large mass in the adrenal gland with pre-contrast density >20 HU, consistent with a solid neoplasm lacking intracellular lipid (oncocytic neoplasm, lipid-poor adenoma, pheochromocytoma).
Marked heterogeneous enhancement in solid components during arterial phase. Enhancement pattern is variable, with hypervascular areas showing intense enhancement while hemorrhage and necrosis areas do not enhance. Enhancement degree may resemble pheochromocytoma — both can show intense arterial enhancement. Washout pattern in delayed phase is variable and washout analysis is not reliable; absolute washout may not meet adenoma criteria (60%).
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Marked heterogeneous enhancement in the adrenal mass during arterial phase, consistent with hypervascular solid neoplasm; washout analysis does not yield reliable results.
Heterogeneous, variable signal intensity on T2-weighted images. Solid components generally show isointense to mildly hyperintense signal. Cystic/necrotic areas demonstrate marked T2 hyperintensity. Hemorrhage areas show variable T2 signal — acute hemorrhage may be hypointense, subacute hemorrhage hyperintense. An intact capsule or pseudocapsule may be visualized as a hypointense linear structure on T2. Unlike the marked T2 hyperintensity of pheochromocytoma ('light bulb sign'), oncocytic neoplasm typically shows lower T2 signal.
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Adrenal mass with heterogeneous signal intensity on T2-weighted images, with isointense to mildly hyperintense solid components and markedly hyperintense cystic/necrotic areas; unlike the marked T2 hyperintensity of pheochromocytoma, this pattern is consistent with oncocytic neoplasm.
No signal drop on chemical shift (opposed-phase) images compared to in-phase images. This results from the absence of intracellular lipid in tumor cells — mitochondrial accumulation occupies lipid storage space. Absence of signal drop excludes lipid-rich adenoma but does not differentiate from lipid-poor adenoma, pheochromocytoma, or adrenocortical carcinoma. Specificity of chemical shift MRI for oncocytic neoplasm is low.
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No signal drop on opposed-phase chemical shift imaging, indicating absence of intracellular lipid; lipid-rich adenoma is excluded, and lipid-poor adenoma, pheochromocytoma, or oncocytic neoplasm should be considered.
Variable diffusion restriction on DWI. Solid components may show mild to moderate diffusion restriction (ADC 0.8-1.2 x 10⁻³ mm²/s). Malignant oncocytic carcinoma shows more pronounced diffusion restriction (low ADC). Necrotic/cystic areas do not show diffusion restriction. DWI cannot definitively differentiate benign oncocytoma from malignant oncocytic carcinoma, but markedly low ADC values should be evaluated in favor of malignancy.
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Mild to moderate diffusion restriction in solid components of the mass with ADC values insufficient for definitive benign-malignant differentiation; histopathological evaluation is recommended.
No uptake on MIBG scintigraphy. Because oncocytic neoplasm is of adrenocortical origin (not medullary origin like pheochromocytoma), it does not express the norepinephrine transporter system and shows no MIBG uptake. This finding is extremely important for differentiation from pheochromocytoma. Malignant oncocytic carcinoma may show mild to moderate FDG uptake on FDG PET-CT, but benign oncocytoma generally shows low uptake.
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No MIBG uptake detected in the adrenal mass, excluding pheochromocytoma and consistent with adrenocortical-origin neoplasm (including oncocytic neoplasm).
Criteria
No Lin-Weiss-Bisceglia major criteria (necrosis, mitotic activity >5/50 HPF, atypical mitoses, venous invasion); at most 1 minor criterion present
Distinct Features
Well-circumscribed, homogeneously encapsulated mass; tendency for more homogeneous enhancement on imaging; less necrosis and hemorrhage; prognosis excellent — no recurrence after surgery
Criteria
No Lin-Weiss-Bisceglia major criteria; but more than 1 minor criterion present (size >10 cm, capsular invasion, sinusoidal invasion, necrosis <25%)
Distinct Features
Imaging features between benign and malignant; larger size and mild heterogeneity; long-term follow-up needed as late recurrence has been reported; clinical-radiological surveillance after surgery recommended
Criteria
At least 1 Lin-Weiss-Bisceglia major criterion present: necrosis, mitotic activity >5/50 HPF, atypical mitoses, or venous invasion
Distinct Features
More heterogeneous on imaging, more extensive necrosis and hemorrhage; irregular margins and capsule disruption may be present; vascular invasion or local invasion findings; more pronounced diffusion restriction on DWI; risk of local recurrence and distant metastasis but better prognosis than conventional adrenocortical carcinoma
Distinguishing Feature
Lipid-poor adenoma is usually <4 cm, homogeneous, well-defined; washout analysis meets adenoma criteria (absolute >60%, relative >40%); oncocytic neoplasm is larger (>6 cm), heterogeneous, and washout analysis unreliable
Distinguishing Feature
Pheochromocytoma shows marked 'light bulb sign' T2 hyperintensity; MIBG positive; catecholamines elevated; oncocytic neoplasm shows lower T2 signal, MIBG negative, catecholamines normal; both can appear as large heterogeneous masses
Distinguishing Feature
Adrenocortical carcinoma is frequently hormonally active (Cushing, virilization), irregularly marginated, invasive; vascular invasion and metastasis more common; oncocytic neoplasm generally non-functional and well-defined; however, malignant oncocytic carcinoma may be indistinguishable from conventional adrenocortical carcinoma on imaging
Distinguishing Feature
Metastasis is usually bilateral, irregularly marginated, unencapsulated with known primary malignancy history; oncocytic neoplasm is unilateral, well-circumscribed, encapsulated without malignancy history; metastasis generally shows more intense FDG uptake on PET-CT
Urgency
routineManagement
surgicalBiopsy
NeededFollow-up
specialist-referralThe fundamental challenge in adrenal oncocytic neoplasm diagnosis and management is the inability to perform preoperative benign-malignant differentiation on imaging. Biochemical evaluation should be performed in all cases (catecholamines — pheochromocytoma exclusion, cortisol/androgen — hormonal activity). Surgical resection (adrenalectomy) is recommended for lesions >4 cm or showing growth. Lin-Weiss-Bisceglia criteria are used for histopathological malignancy assessment. Surgery is curative for benign oncocytoma; long-term follow-up (CT/MRI at 6-12 month intervals) is recommended for borderline cases; adjuvant therapy (mitotane, cisplatin-based chemotherapy) is considered for oncocytic carcinoma, though prognosis is better than conventional adrenocortical carcinoma.
Malignant potential of oncocytic neoplasm is determined by histopathological criteria (Lin-Weiss-Bisceglia criteria). Surgical resection is recommended for large lesions. Preoperative imaging is unreliable for benign-malignant differentiation.