**6.2 Magnetic resonance imaging**

*Basic Principles and Practice in Surgery*

**6. Adrenal image**

5 cm [16].

malignancy.

differentiating adrenal tumors [15].

**6.1 Computed tomography**

virilization [1]. For individuals that present such virilization or high concentrations

Estrogen-producing tumors are rare and they are generally malignant. In men, it may manifest through feminization with gynecomastia, decrease in libido, atrophy of testicles, whereas in women, it could manifest through breast sensitivity and

As previously mentioned, most adrenocortical tumors are benign, nonfunctioning adenomas that were incidentally found in abdominal image examinations such

Adrenal incidentalomas rarely have a malign cause in patients with no known record of cancer. It is estimated that only 2–5% of incidentalomas are formed by adrenal adenocarcinomas, and around 0.7–2.5% of cases are caused by metastasis

Size and some other radiology characteristics of the computed tomography and magnetic resonance imaging might help differentiating an adrenal benign lesion from a malign one, with consequent perioperative implications. Adrenal tumors with surgical indication are generally approached through laparoscopy. On the other hand, in cases when an adrenal adenocarcinoma is suspected, open surgery is preferable, especially for larger lesions (>10 cm), or for those that might expand to other organs [15]. There is a direct relationship between the size of the adrenal tumor and the potential for malignancy. Average size of an adrenal adenocarcinoma at diagnosis is 10–11 cm, whereas most benign adrenal tumors present a diameter smaller than

Besides their larger size, malign adrenal tumors, in most cases, show on image exams as heterogeneous lesions, with irregular margins, suggestive calcifications, and a peripheral enhancement by intravenous contrast due to the core of the necrosis. Expansion toward other organs and lymph node involvement confirm

Adrenal adenomas feature a profuse presence of lipids in their constitution. It is, therefore, very useful to assess the lipid contents by means of density calculation for

The computed tomography is a very important exam in assessing adrenal tumors. At the phase with no contrast, a density calculus is used by means of the Hounsfield units (UH). Lesions with a <10 UH density have a high probability of being benign, whereas most adrenal adenocarcinomas present a >30 UH, which indicates low lipid

Precision of diagnosis may be enhanced by the use of late stages of computed tomography with contrast and the "washout" calculation, which represents the fraction of contrast that is eliminated 10 min after administration. The finding of an average absolute "washout" of 50% after 10 min of contrast used in studies evidenced a 100% sensitivity and specificity for detection of adenomas in relation to adenocarcinomas, pheochromocytoma, and extra-adrenal metastases [17, 18]. All patients likely to be suffering from an adrenal adenocarcinoma should undergo a computed tomography of the thorax prior to surgery as any findings

content. Thus, tumors with density >10 UH demand further assessment.

related to metastasis may alter the approach of treatment.

of androgens, adrenalectomy may be indicated for controlling of hormones.

bleedings [12]. In such cases, adrenalectomy may also be indicated.

as computed tomography and abdomen magnetic resonance imaging.

from tumors elsewhere toward the adrenal [13, 14].

**50**

Despite the fact that the computed tomography is the most important exam in assessing adrenal nodules, in some situations it is imperative to resort to a magnetic resonance imaging.

Analysis of conventional images weighted at T1 and T2 is the most frequently used technique. Adrenal adenocarcinomas present an isointense sign in relation to the T1 liver and enhanced intensity of sign at weighted sequences at T2 (**Figure 4**). Typically, they present as large lesions (>5.0 cm) at the moment of the diagnosis and may include necrosis, bleeding, and, frequently, calcification [19].

After administration of gadolinium, a slight increase of sign is noticed, as well as a swift washout of contrast, whereas malign lesions present a fast and striking increase of sign followed by a rather slow washout pattern [20].

Chemical shift imaging is a detection technique for the presence of lipids. Benign lesions show as relatively shiny at the in-phase images, and they present a dimmed sign at the out-of-phase ones. The majority of adenomas are slightly hypointense or isointense to the liver on T1-weighted images and slightly hyperintense or isointense on T2-weighted images. The utilization of chemical shift techniques (in-phase or out-of-phase GRE) allows the characterization of adenomas containing microscopic fat and water protons in a same voxel (**Figure 5**). On out-ofphase images, the protons signal is null and results in signal loss as compared with in-phase images [21–24].

A magnetic resonance imaging may be superior to a computed tomography in the assessment of the vascular invasion, especially in terms of the inferior vena cava [25, 26].

## **6.3 Other resources of diagnosis per image**

In patients whose characterization of lesion malignancy could not be carried out by a tomography or resonance, additional information could be obtained through fluorine-18 fluorodeoxyglucose positron emission tomography. Malignant lesions present a high collection rate of the radiotracer.

Metomidate binds itself specifically to Cyp11b cortical adrenal enzymes. It is used as a radiotracer at C-MTO PET, as it is capable of differentiating lesions originated at the adrenal cortical from the metastatic ones toward the adrenal [27].

### **Figure 4.**

*Adrenal cortical carcinoma. Magnetic resonance imaging coronal T2-weighted FSE (A) and contrast-enhanced axial T1-weighted GRE (B) sequences demonstrate a large expansive lesion involving the right adrenal gland. The lesion shows heterogeneous pattern of impregnation by the contrast agent and areas of necrosis (hypersignal on T2-weighted sequences) (arrows).*
