Transcript The Problematic Perplexing Parathyroid

The Problematic Perplexing Parathyroid:
A Review of Imaging Pitfalls and Challenging
Parathyroid Adenomas on CT Imaging
Peter Lee, MD
Claudia Kirsch, MD
Vinh Nguyen, MD
ASNR 2016
Objectives
• To discuss the role of parathyroid CT in the
diagnosis of primary hyperparathyroidism.
• To review the typical imaging characteristics of
parathyroid adenomas.
• To describe the imaging pitfalls and
challenging cases of parathyroid adenoma
localization on time resolved CT imaging.
Primary Hyperparathyroidism
• Autonomous overproduction of parathyroid
hormone.
• Incidence: 25/100,000 in the U.S.
• F:M 3:1
• Peak incidence: >50 years
• Sporadic > familial (MEN1, MEN2A)
Primary Hyperparathyroidism
• Symptoms:
– Commonly asymptomatic.
– Renal stones.
– Osteopenia. Bone/joint pain.
– PUD, GERD, pancreatitis.
– Depression, memory loss.
• Labs
– Hypercalcemia
– Elevated parathyroid hormone (PTH)
Spectrum of lesions in primary
hyperparathyroidism
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Solitary parathyroid adenoma: 88%
Double adenoma: 4%
Multiple gland hyperplasia: 6%
Parathyroid carcinoma: < 1%
Surgical Management
1.
Minimally invasive
parathyroidectomy (MIP):
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2.
Small unilateral incision in one
quadrant.
Indication: Solitary parathyroid
adenoma.
Requires accurate preoperative
localization
Fewer complications, better
cosmesis, and shorter operative
time.
Four gland cervical exploration:
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Large transverse incision.
Indications: Negative imaging
studies or recurrent
hyperparathyroidism.
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Surgical Management
• Surgical success:
Decline in
intraoperative venous
parathyroid hormone
level.
• Potential complications:
Recurrent laryngeal
nerve injury,
hypoparathyroidism.
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Imaging Modalities
• Ultrasound and/or nuclear scintigraphy
– First line
– Ultrasound: Accurate for eutopic parathyroid adenomas.
Caveat: Can miss ectopic adenomas.
– Nuclear scintigraphy: Detects eutopic and ectopic
adenomas. Caveat: Low spatial resolution.
• Parathyroid CT
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First or second line
Detects eutopic and ectopic adenomas.
High spatial resolution. Excellent anatomic localization.
Enhancement characteristics improve diagnostic accuracy.
Parathyroid CT Protocol
• No consensus. Protocol variations:
– Noncontrast and 1, 2, or 3 contrast-enhanced
phases.
– Two contrast-enhanced phases only.
• Our protocol:
– Noncontrast and two contrast-enhanced phases
(arterial and venous).
– Coronal and sagittal reformations of all phases.
What the surgeons want to know:
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Number of parathyroid lesions
Location
Size
Diagnostic confidence
Typical Appearance of a Parathyroid
Adenoma on CT
• Noncontrast: Low attenuation compared to
thyroid.
• Arterial phase: Peak enhancement.
• Venous phase: Washout.
– Over 60 HU decrease compared to arterial phase
or
– More washout compared to thyroid gland.
Typical Appearance of a Parathyroid Adenoma
Figure 1a: A lesion posterior to the left
upper pole of the thyroid
demonstrates avid arterial
enhancement (arrow).
Figure 1b: During the venous phase,
the lesion shows washout (arrow).
Findings are consistent with a
parathyroid adenoma.
Artifacts
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Beam hardening artifact
Motion
Washout seen only on reformats
Adenoma seen only on reformats
Optical Illusion due to high density of intraarterial contrast
Beam Hardening Artifact
• Shoulders and clavicles can attenuate the Xray beam and cause beam hardening artifact
in the inferior neck.
Beam Hardening Artifact: Example 1
Figures 2a and 2b: Beam
hardening artifact (blue arrow)
obscures a lesion abutting the
inferior pole of the right
thyroid (orange arrow).
Figure 2a: Arterial phase.
There is a small cleft (red
arrow) separating the lesion
from the thyroid.
The lesion shows arterial
enhancement and venous
washout, compatible with a
parathyroid adenoma.
Figure 2b: Venous phase.
Beam Hardening Artifact: Example 1
(continued)
Figure 2c: The adenoma is
better seen on a sagittal
reformation, but is still
difficult to resolve.
Figure 2d: Color Doppler ultrasound
confirms the parathyroid adenoma by
its echogenicity and vascularity.
Parathyroid CT and ultrasound can be complementary.
Beam Hardening Artifact: Example 2
Figure 3: A lesion in the right
tracheoesophageal groove
(orange arrow) is obscured by
beam hardening artifact (blue
arrows).
Strategies to avoid beam hardening artifact: Ask patient to
depress shoulders, place a towel between shoulders, or use a
shoulder strap.
Motion Artifact
Figure 4a: A lesion in the left
tracheoesophageal groove shows avid
arterial enhancement, compatible with a
parathyroid adenoma (orange arrow).
Figure 4b: However, respiratory motion
artifact more superiorly limits evaluation
for additional adenomas.
Breathing instructions are important for reducing motion artifact.
Washout seen only on reformats
Figures 5a and 5b: A lesion
posterior to the left
hemithyroid midpole does
not appear to wash out on
the axial venous phase.
Figure 5a: Arterial phase
Figure 5b: Venous phase
Figures 5c and 5d: The
lesion does wash out on the
coronal venous phase.
Figure 5c: Arterial phase
Figure 5d: Venous phase
In some cases, venous
washout is seen only
on reformats.
Adenoma seen only on reformats
Figure 6a: Arterial phase.
Figure 6b: Venous phase.
An adenoma abutting the inferior pole of the right hemithyroid is
seen only on the sagittal reformation (arrow). This lesion is not
seen on the axial images (not shown).
Optical Illusion
Figure 7a: Noncontrast.
Note radiolucent thyroid
(blue arrow). This entity
will be discussed on a later
slide.
Figure 7b: Arterial phase.
Figure 7c: Venous phase.
A parathyroid adenoma abutting the right lower pole
(orange arrow) appears to increase in enhancement
between the arterial and venous phases. However, there
is actually a 60 HU washout. This optical illusion is due to
the high density of intra-arterial contrast.
Variant Anatomy and Parathyroid Mimics
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Cystic parathyroid
Radiolucent thyroid
Parathyroid calcifications
Parathyroid mimics
Cystic Parathyroid Adenoma: Example 1
Figures 8a and 8b: Coronal
and axial images demonstrate
a partially cystic mass at the
level of the right hemithyroid
lower pole.
Figure 8b
Figure 8a
Figure 8c
Figure 8d
Figures 8c and 8d: The solid
component of the lesion
demonstrates avid arterial
enhancement (8c) and venous
washout (8d). Findings are
compatible with a partially
cystic parathyroid adenoma.
Cystic Parathyroid Adenoma: Example 2
Figure 9a: Axial arterial phase image
shows a large cystic mass deep to
the left hemithyroid. The mass does
not demonstrate arterial
enhancement or venous washout.
Figure 9b: Venous phase sagittal
reformat better demonstrates
septations within the mass.
Pathology was consistent with cystic
parathyroid adenoma.
Radiolucent Thyroid
Figure 10a: A radiolucent thyroid gland
demonstrates atypically low attenuation on
noncontrast imaging (arrow).
Radiolucent Thyroid (continued)
A lesion inferior to the
left hemithyroid inferior
pole (orange arrow)
shows arterial
enhancement and
venous washout (10d,
10e), compatible with a
parathyroid adenoma.
Figure 10b: Arterial
Figure 10c: Arterial
Figure 10d: Venous
Figure 10e: Venous
Radiolucent thyroids
demonstrate poor
contrast enhancement.
Because washout of
parathyroid adenoma
can be defined relative
to washout of the
thyroid, this can lead to
misdiagnosis.
Parathyroid Calcification
Figure 11a: Arterial phase.
Figure 11b: Venous phase.
There is a calcified lesion (arrow) inferior to the left hemithyroid. Calcifications are
rarely seen in parathyroid adenomas and are more common in parathyroid
carcinoma. In this case, pathology was consistent with adenoma.
Parathyroid Mimic:
Concurrent Lymphoma
Figure 12a and 12b: A lesion in the
left tracheoesophageal groove
(orange arrows) shows mildly
increased enhancement on venous
phase. This may represent an atypical
parathyroid adenoma.
Figure 12a: Arterial phase.
Figure 12b: Venous phase.
The patient had concurrent
lymphoma. Note bilateral cervical
lymphadenopathy (blue arrows), left
greater than right, which can mimic
parathyroid adenomas.
Conclusion
• Parathyroid CT is a first or second line imaging
modality for primary hyperparathyroidism,
offering accurate anatomic localization of eutopic
and ectopic parathyroid adenomas.
• Though there is no consensus, most protocols
include noncontrast and contrast-enhanced
phases.
• Awareness of image artifacts and pitfalls on
parathyroid CT can improve diagnostic accuracy.