Download Thyroid Uptake on FDG PET/CT: What the Radiologist Needs to Know

Thyroid Uptake on FDG PET/CT:
What the Radiologist Needs to
Know
Puneet Belani MD, Mansi Shah, and
Jeffrey Kempf MD FACR
Rutgers - Robert Wood Johnson
University Hospital
New Brunswick, NJ
PURPOSE AND METHODS
• With the increasing use of FDG PET in oncology, unexpected
thyroid uptake is not uncommonly encountered
• The purpose of this educational exhibit is to review the most
commonly encountered uptake patterns of FDG PET in the
thyroid gland and their clinical significance, with review of the
literature
• Selected instructional cases from an academic university based
practice that reflect the most common incidentally encountered
patterns of thyroid uptake on FDG PET/CT are presented
• The two most common patterns for incidental FDG thyroid
uptake are focal as well as diffuse
• Rarely, a diffuse and focal pattern may be also be encountered
•
Patient 1. Coronal and fused axial
FDG Pet images in a patient with
metastatic melanoma and incidental
intense focal thyroid uptake
Case 1
Normal thyroid gland does not take up
significant FDG due to its main energy
substrate of free fatty acids
Thyroid incidentaloma defined as thyroid
uptake incidentally detected; management
can be confusing
“PAIN”- PET associated incidental neoplasm
Many papers in literature with wide
reported incidence of thyroid
incidentalomas on PET in up to 8.9% of
scans.
Overall pooled incidence of thyroid
incidentalomas from meta-analysis of 27
studies in literature reported to be 2.46%
(Bertagna et al. 2012)
Focal Incidental Thyroid Uptake
Malignancy rate:
Generally reported between
approximately 25% to 50%
Overall malignancy ratio from recent
literature meta-analysis: 34.6%
Does SUV help predict Malignancy?
-Many conflicting study results in literature
with overlap of benign and malignant thyroid
nodules
Thyroid Cancer Pathologic Types of Incidentalomas
-Trend towards increasing Suv max and
malignancy but no safe SUV max cutoff
Papillary Thyroid Cancer most common subtypeapproximately 85%, up to 100% in some studies;
may be more aggressive
-Some benign nodules such as Hurthle cell
adenomas and follicular adenomas may be
very hypermetabolic on PET
Follicular, Hurthle cell, poorly differentiated,
anaplastic, medullary, and metastases all reported
-Dual time point imaging not shown to be
generally helpful in differentiating benign
from malignant thyroid nodules
Benign Causes
Follicular pathology/ adenoma
Toxic adenoma
Hurthle cell adenoma
Hemorrhagic cyst
Benign colloid pattern
Hashimoto’s
thyroiditis
Multinodular hyperplasia
Focal Incidental Thyroid Uptake
-
Since there is considerable malignancy risk in FDG avid incidentally
discovered thyroid nodules, and these nodules may be more aggressive,
they should be further evaluated when patient’s clinical condition permits
- NCCN guidelines: include FDG avid thyroid nodules as a high risk clinical
feature (along with radiation exposure as child or adolescent, first degree
relative with thyroid cancer or MEN2, personal history of thyroid cancerassociated conditions)
- ATA guidelines: FDG avid thyroid nodules “require prompt investigation”
-perform thyroid ultrasound; FDG avid thyroid nodules considered high
risk category
- If nodule can be biopsied and patient co-morbidities would not preclude
thyroid surgery, further histological correlation usually attempted
Case 2
Patient 2: 58 y.o. female with breast cancer and brain metastases.
Transaxial and coronal PET, trans-axial PET/CT fusion, and transaxial
CT images demonstrate incidental diffuse symmetric FDG uptake in
the thyroid with SUV max of 7.4
Case 2: Diffuse Uptake
• Diagnosis: Hashimoto’s thyroiditis
• Diffuse uptake is most commonly due to Hashimoto’s thyroiditis
• Other less frequent diagnoses include Graves disease, hormone
replacement therapy for hypothyroidism, thyroid lymphoma,
benign goiter, as well as normal variants
• SUV does not have a predictive value of final diagnosis
Diffuse Incidental Thyroid Uptake
Hashimoto’s Thyroiditis
Most common etiology of incidental diffuse
thyroid uptake on FDG PET; SUV can be variable
AKA Chronic lymphocytic thyroiditis;
autoimmune disorder; may be familial
Most common cause of hypothyroidism in the
US; may result in hyperthyroidism
Common middle age females, but may occur at
any age. Female/Male-8:1; up to 5% adults
May be asymptomatic for years; goiter
Dx: TFT’s, elevated antithyroid peroxidase and
thyroglobulin antibodies
Complications: hypothyroidism,
hyperthyroidism, rarely thyroid cancer
Fine needle aspirations often inaccurate-limits
usefulness in this population
Focal versus Diffuse
Focal incidental >>diffuse
incidental thyroid uptake,
approximately 70% focal/30%
diffuse
Recommendations for diffuse uptake
Physical exam and thyroid laboratory
data (TSH, T4, T3, anti-TPO, and
thyroglobulin antibody) correlation
Diffuse plus focal
Rare. Can be associated with thyroid
malignancy including thyroidal
primary or secondary carcinoma, as
well as thyroid lymphoma possibly
superimposed on a background of
thyroiditis.
Case 3
• Patient 3. 51 y.o. female with
history of lung nodules. Axial
and coronal PET and axial CT
images demonstrate incidental
diffuse intense FDG uptake in
the thyroid gland, with
enlargement of the right lobe.
SUV max 16.5.
Case 3: Thyroid Lymphoma
• Diagnosis: B-Cell Lymphoma
• Primary thyroid lymphomas are practically always non-Hodgkin
lymphomas (NHLs)
• Only 2% of extra nodal lymphomas arise in the thyroid gland and
only up to 2% of thyroid malignancies are thyroid lymphomas
• Primary thyroid Hodgkin disease is extremely rare
• NHLs can be divided into aggressive and indolent cell types
• The most common cell type is diffuse large-cell lymphoma, either
associated or unassociated with mucosa-associated lymphoid tissue
(MALT) lymphoma (MALToma)
• They most frequently arise from lymph nodes, but an extranodal
site can be the primary source in approximately 30% of cases, and
the thyroid gland is among the most common of these extranodal
sites
• Thyroid NHL has a high rate of cure without the need for extensive
surgery
Conclusions
• Thyroid incidentalomas on FDG PET/CT are not infrequent with a
combined incidence of 2.5%
• Incidental focal thyroid uptake is a more common pattern compared to
incidental diffuse thyroid uptake
• Diffuse thyroid uptake most commonly caused by benign disease-most
commonly Hashimoto’s thyroiditis
• About one third to one half of incidental focal thyroid uptake are
malignant, most commonly secondary to papillary thyroid carcinoma; may
be more aggressive sub-types but reports are conflicting
• All thyroid incidentalomas need further investigation and clinical
evaluation
• SUV cutoff values do not play a role in ruling in or ruling out malignancies
in this scenario
• It is therefore important for the radiologist to become knowledgeable of
the importance of the different types of thyroid uptake patterns on FDG
PET scans and to be able to convey to the ordering physician the most
likely diagnostic possibilities as well as further recommendations for
additional thyroidal workup, if needed
References
•
Are C, Hsu JF, Schoder H, et al. FDG-PET detected thyroid incidentalomas: Need for further investigation? Ann Surg Oncol
2007; 14:239–247.
•
Bertagna F, Treglia G, Piccardo A, and Giubbini R. Diagnostic and clinical significance of F-18-FDG-PET/CT thyroid
incidentalomas. JCEM 2012; 97(11): 3866-3875.
•
Cooper D, et al. Revised American thyroid association management guidelines for patients with thyroid nodules and
differentiated thyroid cancer. November 2009. The American Thyroid Association (ATA) Guidelines Taskforce on Thyroid
Nodules and Differentiated Thyroid Cancer. http://thyroidguidelines.net/revised/taskforce. Accessed March 2014.
•
Kwak JY, Kim EK, Yun M, et al. Thyroid incidentalomas identified by 18FFDG PET: sonographic correlation. AJR Am J
Roentgenol 2008; 191: 598–603.
•
Lowe VJ, Mullan BP, Hay ID, et al. 18 FDG PET of patients with Hürthle cell carcinoma. J Nucl Med 2003; 44:1402–1406.
•
Mehdi G, Siddiqui F, and Ali Rizvi SA. Hurthle cell adenoma as an incidental finding in Hashimoto’s thyroiditis - case report
and short review of literature. The Internet Journal of Pathology 2008; 8:1.
•
Pampaloni MH, Win AZ . Prevalence and characteristics of incidentalomas discovered by whole body FDG PET CT. Int J Mol
Imaging 2012; article ID 476763.
•
Shie P, Cardarelli R, Sprawls K, et al. Systematic review: prevalence of malignant incidental thyroid nodules identified on
fluorine18 fluorodeoxyglucose positron emission tomography. Nucl Med Commun. 2009; 30:742–748.
•
Watanabe N, Noh JY, Narimatsu H, et al. Clinicopathological features of 171 cases of primary thyroid lymphoma: a long-term
study involving 24,553 patients with Hashimoto's disease. Br J Haematol 2011; Apr;153(2):236-43.