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Adrenal Disorders


Non-Functional Adrenal Disorders

Non-Hyperfunctioning Adrenal Adenoma

Definition

This is due to non-neoplastic overgrowth of the adrenocortical cells of the zona fasciculate

  • More common in some inherited diseases (e.g. MEN 1/Beckwith–Weidman syndrome/Carney complex)

  • It is detected incidentally in up to 5% of CT examinations ▸ the number and size of any nodules increases with age (but generally they are <6 cm in diameter)

  • Most commonly seen in obese diabetics/elderly women

  • 6% of 60 year olds have an adrenal adenoma (80% of these are benign non-functioning adenomas) ▸ in patients with a known malignancy, only 25–35% of adrenal masses are malignant

Investigation of incidental adrenal mass

  • Biochemical evaluation: hyperfunctioning or non-hyperfunctioning status dictates further management

  • If there is no history of malignancy, a unilateral non-hyperfunctioning adrenal mass rarely, if ever, represents a metastasis (adenoma or carcinoma)

  • Smaller adrenal masses (<4 cm) are more likely to be benign (this is not a reliable indicator)

    • ▪

      Adenomas have an increased intracellular lipid content ▸ if an adrenal mass measures ≤10 HU on a NECT, it is an adenoma (contrast imaging is not required) ▸ if NECT attenuation is >10 HU, it may be a lipid-poor adenoma-further imaging is required

    • ▪

      Even lipid-poor tumours demonstrate a rapid washout of IV contrast medium

    • ▪


  • Washout ≥ 60 % = adrenal adenoma

  • Histogram analysis method: ROI drawn over at least of the adrenal mass (excluding necrosis); pixel attenuation values are plotted against their frequency ▸ 97% of adenomas have negative pixels (metastases have no negative pixels)

MRI

90% of adenomas demonstrate homogenous or ring enhancement (60% of malignant masses have heterogeneous enhancement) ▸ adenomas show early peak enhancement (the value of peak enhancement does not distinguish between adenomas and metastases) ▸ fat-rich adenomas will lose signal on out-of-phase imaging – quantitative analysis can be made using the adrenal – splenic ratio (the liver can be unreliable due to either fatty or iron deposition, and skeletal muscle can undergo fatty infiltration in the elderly)

FDG-PET

Maximum SUV uptake is lower for adenomas than metastases; however 48% of adenomas demonstrate moderate and high FDG uptake and can mimic malignant masses (limiting its role) ▸ quantitative evaluation using a SUV cutoff of 2.68–3.0 has a high sensitivity and specificity for separating benign from malignant masses

    • ▪

      False positive: adrenal adenoma/phaeochromocytoma/inflammatory lesions

    • ▪

      False negative: adrenal metastases with haemorrhage or necrosis/small metastatic nodules/metastases from bronchioloalveolar carcinoma or carcinoid tumours

  • Phaeochromocytomas can have similar attenuation and washout characteristics as an adenoma; if concerned biochemical and clinical evaluation is required

Infection

  • Granulomatous infections (tuberculosis, histoplasmosis, or blastomycosis)

CT

There is bilateral but asymmetric involvement of the adrenal glands ▸ with active infection the adrenal glands are enlarged and heterogeneous (particularly after contrast administration) ▸ they may demonstrate small non-enhancing areas of caseous necrosis (± calcification) during the acute phase or with healing ▸ long-standing infection can result in atrophy of the adrenal glands

  • AIDS patients with extrapulmonary Pneumocystis carinii infection: there may be punctuate or coarse calcification within the adrenal glands (as well as within the spleen, liver, kidney and lymph nodes)

  • Adrenal abscesses: these are rare, with most found in neonates with pre-existing adrenal haemorrhage ▸ an abscess will appear as a thick-walled cystic lesion

Adrenal Hypofunction (Addison's Disease)

Definition

Results from primary adrenal insufficiency or secondary to hypothalamic-pituitary ACTH deficiency ▸ manifests when >90% of the gland destroyed ▸ acute (rare, and usually due to haemorrhage) or chronic

  • Primary insufficiency causes : autoimmune (commonest western cause)/TB (commonest worldwide cause)/AIDS/drugs/adrenal haemorrhage/Waterhouse–Friderichsen syndrome (in the context of septicaemia)/sarcoidosis/amyloidosis/haemochromatosis /congenital

CT/MRI

  • Haemorrhage/haematoma: T1WI and T2WI signal evolves over time ▸ need to exclude an underlying mass lesion (e.g. metastases or melanoma) ▸ an underlying mass may demonstrate enhancement ▸ acute haemorrhage can precipitate an Addisonian crisis, chronic haemorrhage chronically calcify or turn cystic

  • Subacute Addison's disease: hypofunction <2 yrs ▸ usually secondary to adrenalitis – with adrenal hypertrophy ± central necrosis and rim enhancement

  • Calcification: usually seen in granulomatous disease (e.g. TB/sarcoidosis)

  • Chronic changes: the adrenal glands can be extremely small and may be difficult to identify

Contrast-enhanced CT 60 s after contrast medium administration. Both adrenal glands are very small, irregular and difficult to detect. The appearances are typical for autoimmune adrenal atrophy. **

Bilateral adrenal masses. (A) Axial T1- and (B) axial T2-weighted images. Chemical shift imaging: (C) in-phase and (D) out-of-phase images. (E) Post-gadolinium enhanced T1-weighted image with fat saturation. Bilateral adrenal masses seen as homogeneous intermediate T1 signal intensity lesions, low T2 signal intensity and demonstrated rim enhancement following gadolinium administration. In (D), both drop significant visual signal intensity; all the parameters are in keeping with typical lipid-rich adenomas. **

Histogram analysis of adenoma. A small left-sided adrenal lesion is seen on the unenhanced CT. The attenuation value is 14 HU and therefore indeterminate on unenhanced CT alone. On histogram analysis, obtained by drawing a region of interest over the mass, there are pixels ranging between –35 HU and +14 HU (x-axis). The presence of more than 5% negative pixels indicates an adenoma. This was confirmed on washout criteria. **

(A) Axial T1-, (B) coronal T2- and (C) coronal T1-weighted image with fat saturation and gadolinium enhancement of a sporadic large left adrenal haemorrhage in a 43-year-old man. There is a high T1 signal intensity rim, low T2 signal intensity foci within the lesion and no internal contrast enhancement. The lack of internal architecture and enhancement excludes an underlying lesion. **

Adrenal Cysts

Definition

  • These are usually endothelial or epithelial in origin (they may also be parasitic) ▸ pseudocysts (following haemorrhage or necrosis) are more common

Clinical Presentation

  • They are uncommon and usually unilateral (F>M)

  • If large can cause pain

Radiological Features

CT/MRI

Thin-walled cysts with fluid attenuation and signal characteristics ▸ they are non-enhancing ▸ there can be peripheral and curvilinear calcification (15% of cases)

  • T1WI: increased SI can be seen with the presence of proteinaceous material, infectious debris or haemorrhage

  • Solid components/thickened walls/septae suggest possible necrotic mass or infective cyst

Adrenal cyst. (A) CECT showing the typical appearance of a cyst (arrow) within the left adrenal gland. (B) T1WI shows the low signal intensity of a simple cyst (arrow). (C) T2WI shows the uniformly high SI of a fluid-filled lesion (arrow). *

Adrenal Metastases

Definition

  • These most commonly follow tumours of the lung, kidney, breast, GI tract and ovary (and also with melanoma) ▸ they very rarely result in hypoadrenalism

Radiological Features

CT

A metastasis tends to be larger than an adenoma ▸ they are also heterogeneous, less well-defined and have a thick, irregular enhancing rim ▸ they are more commonly unilateral

MRI

T1WI: low SI (compared to liver) ▸ T2WI: high SI (compared to liver)

Pearls

  • The presence of an adrenal mass in a patient with a known malignancy does not necessarily indicate the presence of metastatic disease: 40–50% of lesions are non-metastatic and represent adenomas (even bilateral adrenal masses are more likely to be adenomas rather than metastatic deposits)

  • It may require percutaneous biopsy if the primary is unknown

  • Increased likelihood of malignancy: size >4 cm ▸ rapid size increase

Adrenal metastases. (A) NECT demonstrates bilateral nodular adrenal masses. (B) After chemotherapy, the adrenal masses are smaller. ∫

Adrenal Haemorrhage

Traumatic

  • This is seen on CT in 2% of patients who sustain severe trauma

CT

A round or oval well-defined adrenal haematoma (seen in the majority) is more common than uniform adrenal enlargement or diffuse irregular haemorrhage obliterating the gland

Non-traumatic

  • This is usually associated with: anticoagulants (or other bleeding disorders) ▸ recent surgery or severe burns ▸ sepsis (in particular meningococcal) leading to the Waterhouse–Friderichsen syndrome ▸ hypotension ▸ tumour (particularly a melanoma)

CT

Haemorrhage is unilateral in the majority (R>L) ▸ calcification may develop after a few months ▸ occasionally a haematoma will liquefy and persists as a pseudocyst

  • Acute or subacute phase: the enlarged adrenals are of increased density (50–70 HU)

  • Later stages: there is reduced density and size of the lesion (which usually resolves)

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