European Radiology: Are you still having a headache differentiating adrenal pheochromocytoma from lipodeficiency adenoma?

According to statistics, about 5% of patients detect accidental adrenal nodules
on imaging.
Adrenal metastases can be reasonably excluded by the presence or absence of a personal history of primary malignancy, and adrenal cortical carcinoma (ACC) is extremely rare, radiographically aggressive, and usually > 4 cm
in diameter.
Among routine diagnostic considerations, benign adrenal tumors are the most common, followed by pheochromocytomas
.
Symptomatic pheochromocytoma can be diagnosed clinically; However, pheochromocytoma can be asymptomatic
in 5-58% of cases.

Biochemical testing of incidental adrenal nodules is clinically recommended, and pheochromocytoma has been reported to be diagnosed with greater than 90%
accuracy.
Imaging remains necessary in patients with established pheochromocytoma for localization and surgical planning, especially in patients with multiple nodules
.
In patients with known or suspected concurrent pheochromocytoma, imaging is necessary to screen for further development of pheochromocytoma and paraganglioma.

However, differentiating between pheochromocytoma and adenoma with CT or MRI is a challenge
.
On CT scan, there is some overlap in the imaging features of pheochromocytoma and adenoma.

MRI is also limited in the diagnosis of pheochromocytoma, with approximately 30% of pheochromocytomas absent from the characteristic "bulb-like" T2-weighted (T2W) hyperintensity
.
Recent studies have explored the use of texture analysis or machine learning for radiological features to diagnose pheochromocytoma
.
However, these studies, which applied different radiological analyses to different imaging studies, showed results that lacked validation and were not easily applied to clinical practice
.

A study published in the journal European Radiology evaluated the diagnostic accuracy and reproducibility of adrenal T2WI MRI in distinguishing metastases from adrenal adenomas
in populations with pheochromocytoma and lipodeficiency adenoma.

This study compared 29 consecutive pheochromocytomas resected between 2010 and 2019 with 23 continuous fat-depleting adrenal tumors.

Three radiologists (R1, R2, R3) subjectively assessed T2W signal intensity and heterogeneity and extracted T2W signal intensity ratio (SIR) and entropy
.
These values were grouped into the quantitative and qualitative T2WI adrenal MRI calculator (logistic regression models containing T2W SIR+ entropy and subjective SI [relative to the renal cortex] and heterogeneity), using predefined thresholds to distinguish metastases from adenomas, and using 2×2 table analysis for accuracy
.

Subjectively, all three radiologists agreed that pheochromocytoma was brighter (P < 0.
001) and more heterogeneous (P < 0.
001).

Observer-to-observer agreement was fair to moderate (K = 0.
37-0.
46) and moderate in terms of heterogeneity (K = 0.
24-0.
32)
in terms of T2W signal intensity.
The T2W-SI ratio (P<0.
001) and entropy (P<0.
001) were both higher
than those of pheochromocytoma in all three readers.
The sensitivity, specificity, and accuracy of the quantitative calculator in distinguishing between pheochromocytoma and adenoma were high (100% [95% confidence interval 88–100%], 87% [66–97%], and 94% [86–100%] R1; 93% [77-99%], 96% [78-100%] and 94% [88-100%] R2; 97% [82-100%], 96% [78-100%], and 96% [91-100%] R3).

Qualitative calculators have high specificity, but low sensitivity and overall accuracy (48% [29-68%], 100% [85-100%], and 74% [65-83%]R1; 45% [26-64%], 100% [85-100%], and 72% [63-82%]R2; 59% [39-77%], 100% [85-100%], and 79% [70-88%R3)).

Figure A 48-year-old male patient with 2.
3 cm of fat-fatigued adrenal tumor is diagnosed
by 2 years of stable imaging (not shown) and negative biochemistry.
Axial T2-weighted (T2W) HASTE image, adenoma (arrow) rated by three radiologists as a homogeneous mass, low intensity (not shown) relative to the renal cortex parenchyma

This study suggests that pheochromocytoma assessed by subjective and quantitative assessment has higher T2-weighted signal intensity and heterogeneity
compared with fat-depleted adrenal tumors.
Using existing T2W adrenal MRI evaluation models, high sensitivity, specificity, and overall accuracy
in the diagnosis of pheochromocytoma were achieved through quantitative T2W signal intensity ratio and entropy.

Original source:

Rosalind Gerson,Wendy Tu,Jorge Abreu-Gomez,et al.
Evaluation of the T2-weighted (T2W) adrenal MRI calculator to differentiate adrenal pheochromocytoma from lipid-poor adrenal adenoma.
DOI:10.
1007/s00330-022-08867-4