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PRESENTOR: DR RITUPARNA DAS

ADRENAL IMAGING. PRESENTOR: DR RITUPARNA DAS. NORMAL ANATOMY. The adrenal glands are located in the perirenal space, immediately anterosuperior to the upper pole of the kidneys.

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PRESENTOR: DR RITUPARNA DAS

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  1. ADRENAL IMAGING PRESENTOR: DR RITUPARNA DAS

  2. NORMAL ANATOMY • The adrenal glands are located in the perirenal space, immediately anterosuperior to the upper pole of the kidneys. • The adrenal glands receive blood supply from the superior, middle, and inferior suprarenal arteries, which originate from the inferior phrenic arteries, abdominal aorta, and renal arteries, respectively • Medullary veins emerge from the suprarenal hila to form the suprarenal veins, which drain to inferior vena cava (right side) and left renal vein (left side). • The adrenal gland is composed of an outer cortex and thinner inner medulla.

  3. The right adrenal gland is located immediately posterior to the inferior vena cava and superior to the upper pole of the right kidney. It has a linear, inverted V, or Y configuration • The left adrenal gland is anteromedial to the upper pole of the kidney and posterior to the pancreas; it has a triangular, inverted Y, or V configuration. • Normal adrenal glands range from 2 to 6 mm in thickness and from 2 to 4 cm in length.

  4. IMAGING MODALITIES • USG • CT • MRI • PET SCAN • ADRENAL SCINTIGRAPHY

  5. IMAGING APPEARANCE NORMAL ADRENAL • On cross-sectional imaging, both adrenal glands can be divided into a body, medial and lateral limbs. • The right adrenal body should not exceed 8 mm and the left adrenal body should not exceed 10mm. • The maximum normal adrenal limb thickness is 5 mm. • The normal adrenal demonstrates uniform contrast enhancement on arterial and venous phase CT and the cortex cannot be distinguished from the medulla. • On MRI, both glands have a uniform intermediate T1 and a low-to-intermediate T2 signal intensity and are better demonstrated on T1 fat-saturated images as nulling the signal from surrounding retroperitoneal fat augments the adrenal signal

  6. USG

  7. ultrasound imaging of adrenal carcinoma. (A) Right adrenal mass with 6.1×3.6 cm size, middle uniform echo, and unclear boundary. (B) No notable vascularization is shown

  8. imaging of no necrosis pheochromocytomas. Right adrenal mass with 9.5×5.4 cm size, homogeneous echo, and complete capsule.

  9. Blood flow signals were found both inside and around the lesion by color Doppler examination.

  10. pheochromocytomas with necrosis.Rightadrenal mass with 10.8×8.7 cm size, middle and uneven echo, and visible liquefied area.

  11. pheochromocytomas with necrosis .Left adrenal mass with 5.5×4.1 cm size, middle and uneven echo, and visible liquefied area. Blood flow signals mainly in the lesion but also around the lesion by color Doppler examination.

  12. Typical ultrasound imaging of myelolipoma in Right adrenal 52×39 mm in size and homogenous hyperechoic.

  13. CT Incidentally detected adrenal masses in patients with no known malignancy occur in 5% of all abdominal CT examinations

  14. Lesion Size and Contour • On unenhanced CT, imaging findings that suggest a higher likelihood of malignancy include a large lesion size, irregular contour, heterogeneous appearance and a temporal increase in size. • Lesions greater than 4 cm in diameter have a higher likelihood to be malignant

  15. Intracellular Lipid Content of the Adrenal Mass • The majority (>70%) of adenomas have a high intracellular lipid content. • 10 HU is the most widely used threshold value for the diagnosis of a lipid rich adrenal adenoma • Lesions on unenhanced CT with an attenuation greater than 10 HU require further evaluation with either contrast-enhanced washout CT, MRI or scintigraphy

  16. Contrast Enhancement and Contrast Washout Characteristics • Adenomas enhance rapidly after contrast medium administration and also demonstrate a rapid washout of contrast. Malignant lesions and phaeochromocytomas enhance rapidly but demonstrate a slower washout of contrast medium • The percentage of contrast enhancement washout between enhanced images acquired 60 s after contrast medium administration and the delayed images acquired 15 min after contrast medium administration can be used to differentiate adenomas from malignant lesions

  17. an absolute contrast enhancement washout of 60% or higher has a sensitivity of 86–88% and a specificity of 92–96% for the diagnosis of an adenoma • a relative enhancement washout of 40% or, higher has a sensitivity of 96% and a specificity of 100% for the diagnosis of an adenoma.

  18. Histogram Analysis Method • A region of interest (ROI) cursor is drawn covering at least two-thirds of the adrenal mass.The individual attenuation values of all the pixels in the ROI are plotted against their frequency and the amount of lipid in the mass is proportional to the number of negative pixels • The combination of CT attenuation value <10 HU or > 10% negative pixel content would correctly identify 91% of adenomas compared with 66% using CT attenuation alone

  19. Unenhanced CT of left adrenal mass ,had attenuation -13 HU,lipid rich adenoma

  20. MRI

  21. Conventional Spin-Echo Imaging • Gadolinium-Enhanced Magnetic Resonance Imaging • After gadolinium enhancement, 90% of adenomas demonstrate homogeneous or ring enhancement while 60% of malignant masses have heterogeneous enhancement. • Adenomas show early peak enhancement, and the time to reach peak enhancement is the strongest discriminator between adenomas and malignant adrenal masses.

  22. Chemical Shift Imaging • Adenomas which contain intracellular lipid lose signal intensity on out-of-phase images compared to in-phase images, whereas malignant lesions and phaeochromocytomas, which lack intracellular lipid,remain unchanged. • visual assessment of relative signal intensity loss is accurate in most cases • Quantitative analysis can be made using adrenal-splenic ratio (ASR) and signal intensity index (SII)

  23. The ASR reflects the percentage signal drop-off within the adrenal lesion compared with the spleen and it can be calculated thus: SI adrenal lesion out-of-phase/SI spleen out-of-phase ×100 SI adrenal lesion in-phase/SI spleen in-phase • An ASR ratio of 70 or less has been shown to be 100% specific for adenomas • Signal intensity index uses the same characteristics of the adrenal mass on both in- and out-of-phase imaging and can be calculated thus: In-phase lesion SI -Out-of-phase lesion SI • SII=-----------------------------------------------------------*100 In-phase lesion SI • Signal intensity indices have been shown to discriminate between adenomas and metastases with an accuracy of 100%. Adenomas characteristically have signal intensity indices greater than 5%, whilst metastases have indices lower than 5%

  24. MR Adrenal Spectroscopy • using threshold values of 1.20 for the choline–creatineratio, 0.38 for the choline–lipid ratio and 2.10 for the lipid–creatine ratio enabled adenomas and pheochromocytomas to be distinguished from carcinomas and metastases. • A 4.0–4.3ppm/creatine ratio greater than 1.50 enabled distinction of pheochromocytomas and carcinomas from adenomas and metastases

  25. PET • Whole-body positron emission tomography (PET) with [18F]-fluorodeoxyglucose (18F-FDG) improves the characterisation of malignant adrenal lesions • Quantitative evaluation using standardised uptake values (SUVs) using a cutoff value of 2.68–3.0 separates malignant from benign adrenal masses with a high sensitivity (99%), specificity (92%)

  26. False-positive lesions for malignancy include: adrenal adenomas, phaeochromocytomas, adrenal endothelial cysts, inflammatory and infectious lesions. • False negatives for malignancy:adrenal metastases with haemorrhage or necrosis, small(5–10 mm) metastatic nodules, and metastases from pulmonary bronchioloalveolar carcinoma or carcinoid tumours • The specificity of PET can be improved with the use of [11C]metomidate (MTO), a marker of 11-hydroxylase, as a tracer for adrenocortical tissue. Phaeochromocytomas, metastases to the adrenal gland, and non-adrenal cortical masses are all MTO-uptake negative. Increased uptake in both adenomas and adrenocortical carcinomas

  27. ADRENAL SCINTIGRAPHY • Functional characterisation based on uptake and accumulation of radiotracers. • Tracers such as iodocholesterol-labelled analogues (131I-6--iodomethyl-19-norcholesterol and Se-6--selenomethyl cholesterol) are markers of adrenal cortical tissue. • Adrenal medullaryscintigraphy requires radioiodinatedguanethidine analogues, 131I-MIBG and 123I-MIBG.

  28. ADRENAL INCIDENTALOMAS

  29. ADRENAL ADENOMA • Hypoattenuating,usually <10 HU on NECT • absolute contrast washout >60% • Lose signal intensity on out of phase images

  30. MYELOLIPOMA • Well defined hyperchoic mass on USG • The appearance of myelolipomas on CT depends on their histologic composition. The masses often have a recognisable capsule and may contain calcification. The soft-tissue component usually enhances after administration of intravenous contrast. If there is haemorrhage, high attenuation fluid may be present. The key to CT diagnosis is a focal area of fat in the adrenal mass,some regions with attenuation values less than –30 HU • on MRI, the diagnosis is based on the demonstration of fat in the lesion. Fat has high signal intensity on both T1- and T2-weighted images and marrow elements have low signal intensity on T1-weighted images and intermediate signal intensity on T2-weighted images.

  31. Myelolipoma CoronalCT image shows a 6.5-cm right adrenal mass composed of soft tissue and fat, an appearance consistent with a myelolipoma

  32. ADRENAL CYSTS • Cystic lesion on USG • Homogeneous near water attenuating lesion on NECT. wall may show enhancement • Simple cysts are hypointense on T1-weighted images and hyperintense on T2-weighted images, with no softtissue component and no internal enhancement

  33. LYPHANGIOMA • Homogeneous hypoattenuating lesion on CT • Thin walled cysts with low signal intensity on T1 and high signal intensity on T2

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