1
Q
Retroperitoneal Anatomy
What are the compartments of the retroperitoneum?
What is in each compartment?
What is special about one of the compartments?
A
- The retroperitoneum can be separated into three compartments by the anterior and posterior renal fascia and the lateral conal fascia.
- The adrenals and kidneys are located within the perirenal space of the retroperitoneum.
- The ascending and descending colon, the second and third portions of the duodenum, and the pancreas are located in the anterior pararenal space of the retroperitoneum.
- The third compartment of the retroperitoneum, the posterior pararenal space, is a potential space that is clinically important as a pathway for potential disease spread due to secondary involvement of inflammation or neoplasm.
2
Q
Liposarcoma
What are they? 10-15% arise from what area?
What is the most common subtype? Appearance?
In order of increasing malignancy, what are the other subtypes? The appearance of more malignant types?
A
- Liposarcomas are a diverse group of neoplasms that make up the most common primary retroperitoneal tumors. 10-15% of all liposarcomas arise from the retroperitoneum.
- The most common type of liposarcoma is the well-differentiated group, which is composed of adipocytic, sclerosing, and inflammatory subtypes. Adipocytic liposarcoma resembles a lipoma, predominantly composed of fat with strands of tissue representing collagen bands.
- In order of increasing malignancy, liposarcomas may also be myxoid, round-cell, pleomorphic, or dedifferentiated. The more aggressive subtypes may have minimal or no areas of macroscopic fat and may be indistinguishable from other malignant soft-tissue masses.
3
Q
Retroperitoneal Fibrosis
What is it?
Compare to malignant retroperitoneal adenopathy.
A
- Retroperitoneal fibrosis is a rare inflammatory disorder causing increased fibrotic deposition in the retroperitoneum, often leading to ureteral obstruction.
- Unlike malignant retroperitoneal adenopathy, retroperitoneal fibrosis tends not to elevate the aorta off the spine.
4
Q
Adrenals
What is their primary role?
Secondary role?
What are the two distinct components and where are they derived?
A
- The adrenal glands are inverted Y-shaped endocrine glands, which primarily mediate the stress response by releasing cortisol and catecholamines. The adrenals are also a site of secondary sex hormone synthesis and blood pressure regulation (with aldosterone).
- The two distinct components to the adrenal glands are the cortex and the medulla, which are derived from completely different embryological origins (the cortex is derived from mesothelium; the medulla is derived from neural crest) and are susceptible to different diseases.
5
Q
Adrenal Medulla
What is it and what does it produce?
Pathology of the adrenal medulla includes what?
A
- The adrenal medulla is the central portion of the adrenal gland and produces the catecholamines norepinephrine and epinephrine, which are derived from tyrosine.
- Pathology of the adrenal medulla includes pheochromocytoma and the neuroblastic tumors (ganglioneuroma, ganglioneuroblastoma, and neuroblastoma). Neuroblastoma is the most common extracranial solid tumor of childhood.
6
Q
Adrenal Cortex
What is synthesized here?
Pathology of the adrenal cortex (that can be diagnosed on imaging) includes what?
A
- The adrenal cortex synthesizes the steroid hormones aldosterone, glucocorticoids, and androgens, which are all biochemical derivatives of cholesterol.
- Each of the three layers of the adrenal cortex synthesizes one type of hormone:
- Zona glomerulosa (most superficial): Produces aldosterone.
- Zona fasciculata : Produces glucocorticoids in response to pituitary adrenocorticotropic hormone - ACTH.
- Zona reticularis (deepest; closest to the adrenal medulla): Produces androgens.
- MNEMONIC - GFR - The deeper you get you go from salty to sexy!
- Pathology of the adrenal cortex that can be diagnosed on imaging includes adrenal hyperplasia, adrenal adenoma, and adrenal cortical carcinoma.
7
Q
Hyperfunctioning Biochemical Diseases of the Adrenals
What are they?
What do they synthesize?
A
- Cushing syndrome is excess cortisol production from non-pituitary disease, such as idiopathic adrenal hyperplasia, adrenal adenoma, or ectopic/paraneoplastic ACTH (e.g., from small cell lung cancer).
- Cushing disease is excess cortisol production driven by excessive pituitary ACTH.
- Conn syndrome is excess aldosterone production, most commonly from an adrenal adenoma, which causes hypertension and hypokalemia. The adenomas implicated in Conn syndrome are typically small and may be difficult to detect on CT. Localizing the side of excess hormone production with venous sampling may be a helpful diagnostic adjunct.
- Adrenal cortical carcinoma is a very rare adrenal malignancy that arises from the cortex and typically causes a disordered increase in all cortical adrenal hormones and precursors.
- Pheochromocytoma is a usually benign tumor of the adrenal medulla that causes an increase in catecholamines.
8
Q
Hypofunctioning Biochemical Diseases of Adrenals
What are some causes?
Some specifics?
A
- Significant destruction of the adrenals is required to produce adrenal insufficiency.
- Although usually not an imaging diagnosis, Addison disease represents chronic adrenocortical insufficiency and may be caused by autoimmune destruction of the adrenal glands or as a sequela of infection.
- Waterhouse-Friderichsen syndrome is post-hemorrhagic adrenal failure secondary to Neisseria meningitidis bacteremia.
- Idiopathic adrenal hemorrhage is usually unilateral and rarely causes adrenal hypofunction.
9
Q
Adrenal Adenoma
What is it? What can be a possible presentation?
What is the best test to evaluate presence of adrenal adenoma in the presence of suspicious clinical sx or labs?
What is a common clinical scenario in which the need to differentiate this vs what?
How do you reliably diagnose an adrenal adenoma?
If there is a questionable adrenal adenoma in a patient with known lung cancer and no known mets what can you do?
A
- Adrenal adenoma is a benign tumor of the adrenal cortex. Adenomas are usually incidental, but they may occasionally produce excess aldosterone to cause secondary hypertension (Conn syndrome). Non-contrast imaging of the adrenal glands is the best test to evaluate for the presence of an adrenal adenoma in the presence of suspicious clinical symptoms or lab values.
- A common clinical scenario is the need to differentiate between an adrenal adenoma and an adrenal metastasis in the staging of a patient with known malignancy. The diagnosis of an adenoma is made by the detection of intracellular lipid.
- An adrenal nodule attenuating <10 HU can be reliably diagnosed as an adenoma with no further imaging or follow-up needed. most (80%) adenomas are lipid-rich and will attenuate below this cutoff. Up to 20% may be lipid-poor adenomas, which attenuate >10 HU and are not able to be diagnosed on a noncontrast CT.
- An indeterminate (>10 HU), small, homogeneous adrenal lesion in a patient without a known malignancy is overwhelmingly likely to represent a lipid-poor adenoma, and advanced imaging is usually not required in such cases.
- If the nodule in question attenuates >10 HU and clinical confirmation of an adenoma is necessary for clinical management (for instance, in a patient with lung cancer and no evidence of metastatic disease but with an indeterminate adrenal nodule), then get adrenal washout CT or in- and out-of-phase MRI.
10
Q
What is a “collision tumor”?
A
- A collision tumor represents metastasis into an adrenal gland with a pre-existing adenoma.
- If an “adenoma” appears heterogeneous or has shown an interval increase in size, then a collision tumor should be considered in a patient with a known primary even if a region attenuates <10 HU.
11
Q
MRI Adrenal Imaging
What do adenomas contain that are used to help in diagnosis?
What does MRI do to take advantage of this?
What is chemical-shift imaging? What sequence is it based off?
What other malignancies would also lose signal on out-of-phase images?
A
- Adenomas contain intracytoplasmic lipid due to steroid production. MRI is able to detect even a small amount of intracytoplasmic lipid that may be undetectable on CT by taking advantage of the fact that protons resonate at different frequencies in fat and in water.
- Chemical shift imaging consists of images obtained both in-phase and out-of-phase. When fat and water are contained within the same voxel, out-of-phase images show fat drop-out of signal because fat protons are more shielded and resonate at a slower frequency. Chemical shift imaging is based on T1 images.
- Adenomas suppress on out-of-phase images, while metastases generally do not.
- A short list of malignancies do contain intracytoplasmic lipid and thus would also lose signal on out-of-phase images:
- Well-differentiated adrenocortical carcinoma (very rare).
- Clear cell renal cell carcinomas metastatic to the adrenal gland.
- Hepatocellular carcinoma metastatic to the adrenal gland.
- Liposarcoma (typically a predominantly fatty mass that is rarely confused with adrenal adenoma).
12
Q
Adrenal CT Imaging
Which demonstrate more rapid contrast washout - adenomas or mets?
Timing of the washout phase?
% Washout calculation? What is diagnostic of adrenal adenoma?
What can you do if unenhanced CT is not available or not performed due to radiation exposure concern?
When is adrenal mass biopsy indicated?
A
- Adrenal adenomas demonstrate more rapid contrast washout than metastases do. The more rapid contrast washout of benign adenomas appears to be true even compared to adrenal metastases of hypervascular primaries.
- The timing of the washout phase remains controversial, with recent evidence suggesting 15-minute washout has greater sensitivity than 10 minutes.
- >60% absolute washout is diagnostic of adenoma
- enhanced - delayed / enhanced - unenhanced attenuation (E-D/E-U)
- If unenhanced CT is not available or not performed due to concern for radiation exposure
- >40% relative washout is diagnostic of adenoma:
- %relative washout = E-D/E
- In a patient with a known primary malignancy, lesions that do not demonstrate benign washout kinetics are suspicious for, but not diagnostic of, metastasis.
- Adrenal mass biopsy is indicated for an indeterminate adrenal mass after full imaging workup remains nondiagnostic. Biopsy is safe and generally very accurate.
13
Q
Adrenal Myelolipoma
What is it?
How to diagnose?
Don’t confuse this with what?
A
- An adrenal myelolipoma is a benign neoplasm consisting of myeloid cells (i.e., erythrocyte precursors - not “myo” as in muscle) and fat cells.
- An adrenal mass with any discrete focus of macroscopic fat is virtually diagnostic of a myelolipoma. Exceedingly rare cases of adrenocortical carcinoma and metastatic carcinoma have been reported to contain macroscopic fat. A retroperitoneal liposarcoma may mimic a myelolipoma, although liposarcoma typically presents as a large mass that may displace, rather than arise from, the adrenal.
- An adrenal myelolipoma should not be confused with a renal angiomyolipoma (AML). These two entities are unrelated, although they do have similar names, are located in adjacent organs, and are both diagnosed by the presence of macroscopic fat.
14
Q
Adrenal Cysts
Prevalence?
Imaging appearance?
Most common type?
Second most common type?
Rare type?
Treatment?
A
- Adrenal cysts are uncommon but have imaging characteristics typical of cysts elsewhere (thin, smooth, nonenhancing wall, and water-attenuation internal contents).
- Endothelial adrenal cysts are the most common (45%) type and may be lymphatic or angiomatous in origin.
- Pseudocysts secondary to adrenal hemorrhage represent 39% of adrenal cysts and lack an epithelial lining. Peripheral calcification may be present.
- Epithelial cysts are rare, comprising only 9% of adrenal cysts.
- Occasionally an adrenal cyst may have a complex appearance that may be difficult to differentiate from a cystic/necrotic neoplasm. In such a case, percutaneous aspiration or surgical resection may be considered.
- Small, asymptomatic, simple cysts can be ignored. A cyst may rarely grow so large as to cause symptoms, such as dull pain or compression of the stomach/duodenum, in which case surgery may be indicated.
- Very rarely, hydatid disease may affect the adrenal glands, typically producing a complex cystic lesion with an internal membrane.
15
Q
Pheochromocytoma
What is it?
Symptoms?
What is the name for an extra-adrenal pheo? Most common location? Rare location causing distinctive clinical presentation?
H&N locations/names?
Nuclear med study?
Classic MRI appearence?
A
- Pheochromocytoma is a neoplasm of chromaffin cells, usually arising from the adrenal medulla.
- Pheochromocytoma may cause hypertension and episodic headaches/ diaphoresis.
- The “rule of 10’s” is a general rule characterizing the features of pheochromocytomas.
- Pheochromocytoma is associated with several syndromes.
- An extra-adrenal pheochromocytoma is a paraganglioma. The most common intraabdominal location of a paraganglioma is the organ of Zuckerkandl, located at the aortic bifurcation. A rare intra-abdominal location of a paraganglioma is the bladder, producing the distinctive clinical presentation of post-micturition syncope (syncope after urination).
- Paragangliomas occur in the head and neck in characteristic locations. Paragangliomas of the head and neck are generally called glomus tumors and may be associated with the tympanic membrane (glomus tympanicum), the jugular foramen (glomus jugulare), the carotid body (called a carotid body tumor), or the vagus nerve (glomus vagale).
- Nuclear medicine studies can be used in the workup of pheochromocytoma. of note, I-123 MIBG is used for metastatic workup of adrenal pheochromocytoma and Indium-111 pentetreotide (an analog of octreotide) is used as tracer for localization of a paraganglioma.
- In theory, pheochromocytoma should be diagnosed by urine/plasma metanephrines before imaging is performed, with imaging used for localization and staging. In clinical practice, CT is often employed based on suspicious symptoms (such as episodic hypertension or other appearance of catecholamine excess).
- The classic MRI appearance of pheochromocytoma is a hyperintense mass on T2-weighted images. When large, pheochromocytoma may appear heterogeneous on MRI and CT.
16
Q
Pheochromocytoma
“Rule of 10s”
Syndromes it is associated with?
A
- The “rule of 10’s” is a general rule characterizing the features of pheochromocytomas:
- 10% are extra-adrenal.
- bilateral.
- malignant.
- familial or syndromic.
- Pheochromocytoma is associated with several syndromes:
- Multiple endocrine neoplasia (MEN 2A and 2B): Typically bilateral intra-adrenal pheochromocytomas.
- VHL
- NF1
- Carney’s triad (gastric leiomyosarcoma, pulmonary chondroma, and extra-adrenal pheochromocytoma).
- MNEMONIC: PGP
17
Q
Adrenal Cortical Carcinoma
Prevalence?
Are they always functioning? If so, how would it manifest?
Imaging presentation?
A
- Adrenal cortical carcinoma is a very rare malignancy, with a prevalence of approximately 1/1,000,000.
- Approximately 66% are functional, producing a disordered array of hormones that may manifest as Cushing syndrome, hyperaldosteronism, and virilization.
- Adrenal cortical carcinoma usually presents on imaging as a large, heterogeneous mass. Central necrosis and hemorrhage are typical.
18
Q
Metastatic Disease to Adrenals
How common is it with someone with a known primary?
Most common adrenal metastasis?
A
- Autopsy studies show adrenal metastases are present in >25% of patients with a known primary.
- Lung cancer and melanoma are the most common adrenal metastases.
19
Q
Adrenal Lymphoma
How common is it?
A
- Primary adrenal lymphoma is rare.
20
Q
Adrenal Hemorrhage
What are the causes? If it is caused by anticoagulation when does it typically occur?
Which adrenal gland is more commonly involved?
Appearance? Most important clue?
Does it enhance? What would it look like on follow-up studies?
A
- Adrenal hemorrhage can be spontaneous or due to anticoagulation. When secondary to anticoagulation, the hemorrhage typically occurs within the first few weeks of beginning anticoagulation.
- Hemorrhage involves the right adrenal gland more commonly than the left.
- Hemorrhage may appear mass-like and is often of heterogeneous attenuation on CT. The most important clue is a new adrenal mass within a short time interval if priors are available.
- Hemorrhage does not enhance and decreases in size on follow-up studies.
21
Q
What causes adrenal hyperplasia?
A
Prolonged stress response or ectopic ACTH secretion.
22
Q
Adrenal Calcifications
Does it usually cause hypofunction?
What can it be due to?
A
- Adrenal calcification rarely causes adrenal hypofunction.
- Adrenal calcification can be due to Wegener granulomatosis, tuberculosis, histoplasmosis, or old hemorrhage.
