typically goiter extension is into the retrosternal space , as described back in 1934 by lahey and swinton , for several reasons .
these include the lack of thyroid gland anatomic restraint inferiorly , downward traction caused by the swallowing mechanism , and negative intrathoracic pressure due to respiration .
the finding of retropharyngeal extension via pretracheal and retroesophageal spaces is very rare , only described in a handful of case reports . in routine clinical practice , background thyroid gland fluorine-18-fluorodeoxyglucose
( f - fdg ) uptake on positron emission tomography ( pet ) is routinely encountered .
diffuse increased f - fdg uptake throughout the gland has been shown to correlate with chronic thyroiditis and nodular goiter among other etiologies .
observational studies have found an association between invasive breast cancer and chronic thyroiditis , although the mechanism has not been elucidated .
some suggest that development of thyroiditis in patients with invasive breast cancer may convey a more favorable prognosis .
we present a case of an intensely f - fdg avid large goiter with a standardized uptake value maximum ( suvmax ) of 16.1 with superior extension into the retropharyngeal / prevertebral compartment found incidentally in a patient with invasive ductal breast cancer .
a 68-year - old female patient was found to have a new left breast mass on screening mammogram .
subsequent diagnostic mammography revealed a 2 cm , highly suspicious mass in the left breast at 1 oclock along with morphologically abnormal lymph nodes in the left axilla .
ultrasound - guided core biopsies of the left breast mass , and one axillary lymph node were performed , consistent with infiltrating , well - differentiated ductal carcinoma with focal lobular features ( tubulolobular carcinoma ) .
the tumor was estrogen receptor 50% positive , progesterone receptor 20% positive , and her-2/neu was negative by fluorescence in situ hybridization ( fish ) .
the patient underwent bilateral breast gadolinium - enhanced magnetic resonance imaging which revealed another suspicious area in the left breast , at 10 o clock position , for which ultrasound - guided biopsy revealed similar pathological features .
the patient has a history of hypothyroidism and has been on 50 mcg levothyroxine daily for greater than a year
. physical examination revealed firm diffuse bilateral thyroid enlargement , with both lobes partially underlying the sternocleidomastoid muscles .
her breast cancer was staged as pt2n2a by ajcc seventh edition . a staging f - fdg pet - computed tomography ( ct ) scan performed prior to chemotherapy revealed diffuse postsurgical changes in the left breast and axilla .
in addition , a diffusely f - fdg avid goiter was present ( suvma  16.1 ) with superior extension into the retropharyngeal and prevertebral space [ figures 13 ] .
correlating noncontrast ct scan of the neck demonstrated a large goiter with bilateral thyroid lobe enlargement .
the right thyroid lobe measured 3.3 cm  4.0 cm  10 cm with extensive sub - sternal , superior and posterior extension , resulting in mild leftward tracheal deviation [ figure 4 ] .
68-year - old female with newly diagnosed breast cancer found to have markedly enlarged fluorodeoxyglucose avid goiter with retropharyngeal extension .
( a ) fluorine-18-fluorodeoxyglucose positron emission tomography / computed tomography coronal reformatted images of the neck and mediastinum including noncontrast computed tomography , fluorine-18-fluorodeoxyglucose positron emission tomography , and fused images demonstrate enlarged bilobar goiter with diffuse fluorodeoxyglucose avidity ( white circles ) .
( b ) fluorine-18-fluorodeoxyglucose positron emission tomography / computed tomography sagittal reformatted images of the neck including noncontrast computed tomography , fluorine-18-fluorodeoxyglucose positron emission tomography , and fused images demonstrate superior extension of the goiter into the retropharyngeal and prevertebral space ( white circles ) .
68-year - old female with newly diagnosed breast cancer found to have markedly enlarged fluorodeoxyglucose avid goiter .
serial fused computed tomography / fluorine-18-fluorodeoxyglucose positron emission tomography coronal reformatted images of the neck from fluorine-18-fluorodeoxyglucose positron emission tomography / computed tomography scan demonstrate diffusely intense fluorine-18-fluorodeoxyglucose avidity throughout the bilobar goiter , suvma  16.1 ( white circles ) .
68-year - old female with newly diagnosed breast cancer found to have markedly enlarged fluorodeoxyglucose avid goiter with retropharyngeal extension .
serial fused computed tomography / fluorine-18-fluorodeoxyglucose positron emission tomography sagittal reformatted images of the neck from fluorine-18-fluorodeoxyglucose positron emission tomography / computed tomography scan demonstrate extent of retropharyngeal and prevertebral space involvement ( white circles and black arrows ) .
68-year - old female with newly diagnosed breast cancer found to have markedly enlarged bilobed goiter with retropharyngeal extension .
coronal noncontrast enhanced computed tomography with coned down view of the neck shows bilobar thyroid gland enlargement resulting in mild leftward tracheal deviation ( white circle ) .
blood work showed normal total t3 , free t4 , and thyroid - stimulating hormone with high titers of anti - thyroglobulin antibody ( 998 iu / ml ) and thyroid peroxidase antibody ( 2337 iu / ml ) .
an ultrasound - guided fine needle aspiration was performed and pathology was consistent with chronic thyroiditis .
the patient received adjuvant chemotherapy with docetaxel and cyclophosphamide for six cycles , followed by adjuvant chest wall radiation .
the role of f - fdg pet / ct in cancer imaging has increased exponentially over the past decade for diagnosis , staging , and evaluation of treatment response .
this has subsequently resulted in increased detection of incidental lesions , including thyroid disease . under normal circumstances
, the thyroid gland should not be visualized by pet due to free fatty acids being the preferred substrate for the thyroid gland . in 2006 , choi et al .
, found incidental focal f - fdg avid thyroid nodules in 4% of cases , with associated risk of thyroid malignancy of 36.7% .
while focal thyroid lesions have been found to be associated with malignancy , diffuse thyroid gland uptake has been shown to correlate more with chronic thyroiditis and hypothyroidism .
as lymphocytes become attracted to the thyroid gland , many believe that these activated lymphocytes display greater glucose metabolism and thus play a key role in the uptake process .
additional mechanisms suggested for the increased f - fdg uptake include cell apoptosis and active formation of fibrosis .
a complex association has been demonstrated between thyroid disease and breast cancer dating back to 1896 where breast cancer patients were treated with oophorectomy and thyroid extract .
studies have shown that patients with thyroid dysfunction have a higher prevalence of breast cancer .
furthermore , a higher prevalence of antithyroid antibodies has been found in women with breast cancer compared with healthy controls .
the presence of thyroid autoimmunity in a patient with breast cancer has even been associated with a favorable prognosis .
in addition , diffuse thyroid gland f - fdg uptake in patients with advanced breast cancer ( mean suvmax of 3.2 ) related to autoimmune thyroiditis has also been demonstrated to be an independently favorable prognostic factor
. a significantly increased prevalence of goiter has also been demonstrated in patients with breast cancer compared to control group smyth et al .
, were able to show that thyroid gland volume had prognostic implications for breast cancer patients .
regarding f - fdg uptake , a positive linear correlation has been shown between suvmax and thyroid gland volume in patients with breast cancer .
our patient with breast cancer had a diffuse goiter visualized on fdg - pet scan with suvmax of 16.1 , which is much higher than previously reported .
the increased suvmax may be explained by the extensive bilobar enlargement , correlating with positive linear correlation described previously .
in addition , a superior extension to the retropharyngeal space via pretracheal and retroesophageal spaces are very rare . finally , intense diffuse fdg uptake in a goiter that extends superiorly , as in our case , has never been previously reported to our knowledge .
as discussed previously , our patient with breast carcinoma and a history of chronic thyroiditis was found to have a rare , fdg avid large bilobed goiter with a retropharyngeal extension on staging f - fdg pet / ct examination .
studies have suggested patients with concomitant breast carcinoma and chronic thyroiditis have a more favorable prognosis . to this date
, our patient remains cancer - free which may be partially attributable to the inflamed thyroid gland providing additional immunity .
 diffuse increased fluorine-18-fluorodeoxyglucose ( 18f - fdg ) avidity on positron emission tomography ( pet ) scans has been demonstrated in patients with chronic thyroiditis , likely secondary to increased inflammatory cell glucose uptake . 
 a complex association has been demonstrated between breast cancer and thyroid disease , although the mechanism remains elusive . 
 development of chronic thyroiditis and/or goiter in breast cancer patients has been suggested to convey a more favorable prognosis . 
 goiter extension is almost exclusively into retrosternal space , with only a handful of cases reported with superior extension into retropharyngeal space . 
 we present a rare case of a diffusely enlarged goiter extending superior and posterior into the retropharyngeal space with an associated intense 18f - fdg avidity standardized uptake value maximum ( suvmax ) of 16.1 in a patient with invasive ductal breast cancer . to our knowledge , this represents the first published case of diffusely 18f - fdg avid goiter with retropharyngeal extension . 
INTRODUCTION
CASE REPORT
DISCUSSION
CONCLUSION
Financial support and sponsorship
Conflicts of interest