Keywords
Breast neoplasms - incidental findings - parathyroid neoplasm - radionuclide imaging
Introduction
Primary hyperparathyroidism is characterized by hypercalcemia with a concomitant inappropriately
elevated level of parathyroid hormone. The definitive therapy for primary hyperparathyroidism
is surgery. In the era of minimally invasive surgery, parathyroid imaging has been
used as preoperative tool to identify abnormal parathyroid tissue and allow the surgeon
to help plan an appropriate operative approach. Ultrasound and technetium-99m methoxyisobutylisonitrile
(Tc-99m MIBI) with single-photon emission computed tomography and computed tomography
fusion (SPECT/CT) is the most commonly used protocol in major hospitals for the detection
of parathyroid lesions. The technological advances and rapidly increasing availability
of imaging modalities have led to the discovery of asymptomatic incidentalomas. We
report a patient with primary hyperparathyroidism who underwent parathyroid imaging
and incidentally found to have breast carcinoma detected by the Tc-99m MIBI SPECT/CT.
Case Report
A 55-year-old female with primary hyperparathyroidism was referred for parathyroid
scintigraphy to identify and locate the parathyroid adenoma preoperatively. The 2-hour
delayed Tc-99m MIBI SPECT/CT of the neck and chest detected a small area of mild activity
adjacent to the posteromedial aspect of the right upper thyroid lobe which subsequently
proved to be parathyroid tissue along with multinodular goiter after right upper pole
parathyroidectomy and total thyroidectomy. In addition, there was an incidental finding
of a mild MIBI-avid 1.3-cm right breast nodule [Figure 1]. Further investigations including mammography and ultrasonography of the breast
were performed that reported a spiculated mass about 1.5 cm × 0.7 cm in the right
breast categorized as Breast Imaging-Reporting and Data System (BI-RADS) 5, highly
suggestive of malignancy [Figure 2]. After confirmation of breast carcinoma by core-needle biopsy, breast-conserving
surgery and sentinel lymph node biopsy followed by axillary node dissection were performed
in the same setting with parathyroidectomy. Pathology of the breast mass reported
invasive ductal carcinoma (grade 1) without lymphovascular invasion. One of the sentinel
lymph nodes was positive. Immunohistochemistry studies of estrogen receptor, progesterone
receptor, HER2/neu, and Ki-67 were positive 90%, positive 90%, negative 30%, and positive
30% of tumor nuclei, respectively. The patient received standard adjuvant therapy.
No recurrence was found after 5 years of follow-up.
Figure 1 The planar images of technetium-99m methoxyisobutylisonitrile of the neck and chest
(upper row) showed an incidental finding of focal uptake at right breast (arrow).
Noncontrast computed tomography of the chest (middle row) demonstrated a 1.3-cm breast
nodule at right breast corresponding with the technetium-99m methoxyisobutylisonitrile
lesion. Further inspection of the corresponding fusion images of single-photon emission
computed tomography and computed tomography (lower row) showed nonfunctioning breast
nodule
Figure 2 A correlative ultrasonography confirmed the presence of mass with spiculated margins,
1.5 cm × 0.7 cm at the right breast
Discussion
Among the available imaging modalities, mammography is the preferred modality for
early screening of breast cancer. However, mammography has limitations due to decreased
sensitivity in women with dense breast tissue, limiting its utility in younger women.
Ultrasonography has been reported to identify more cancers than mammography alone.
Magnetic resonance imaging is recommended as an adjunct to mammography in selected
high-risk patients, such as patient with BRCA1 or BRCA2 gene mutation and a history
of chest radiation. Functional breast imaging techniques include breast-specific gamma
imaging, positron emission tomography, and positron emission mammography. These techniques
provide functional assessment of breast lesions at the cellular and metabolic level.
Breast-specific gamma imaging is performed after intravenous injection of the radioisotope
Tc-99m MIBI. In the past, this technique was found to be unable to detect subcentimeter
cancers due to poor resolution of the detector. Currently, the development of high-resolution
detector cameras have led to improved results.[1] However, breast-specific gamma imaging has not been validated as an effective screening
technique in large-scale multicenter prospective studies. In addition, radiation exposure
remains a significant concern. The false-positive results are common and arise from
benign cellular proliferative process such as abscess, fibroadenoma, fibrocystic disease,
unilateral lactating breast, papilloma, and postsurgical scar. Benign breast conditions,
such as active lactation or gynecomastia, can also take up Tc-99m MIBI but appear
as bilaterally homogeneous uptake.[2]
Tc-99m MIBI is a lipophilic cation that can accumulate within cytoplasmic mitochondria.
Therefore, an area of highly metabolically active cancer cells can be detected. Physiologic
distribution of Tc-99m MIBI is commonly seen in several organs, including thyroid,
myocardium, breasts during lactation, liver, gallbladder, bowels, kidneys, and urinary
bladder. It is eliminated through both urinary and hepatobiliary excretion. Although
Tc-99m MIBI is widely used for the evaluation of cardiac perfusion and hyperfunctioning
parathyroid gland, it might be used as a tumor-imaging agent in thyroid, parathyroid,
breast, and lung cancers. There are previous case reports showing that Tc-99m MIBI
could detect noncardiac or nonparathyroid abnormalities such as benign lesions,[3],[4] Graves' disease, Hashimoto's thyroiditis, follicular adenoma, multinodular goiter,
pneumonia, osteomyelitis, and malignant lesions[5],[6],[7],[8],[9] as breast carcinoma, esophageal carcinoma, hepatocellular carcinoma, non-Hodgkin's
lymphoma, and osteosarcoma.
Conclusion
Although the main purpose for using Tc-99m MIBI is the evaluation of functioning parathyroid
lesion or cardiac function, an incidental lesion, especially focal uptake of Tc-99m
MIBI together with corresponding CT abnormality in the breast or other nontargeted
organs, should not be overlooked. Appropriate precaution with adequate further investigations
may lead to an earlier diagnosis and treatment of unexpected significant disease.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms.
In the form the patient(s) has/have given his/her/their consent for his/her/their
images and other clinical information to be reported in the journal. The patients
understand that their names and initials will not be published and due efforts will
be made to conceal their identity, but anonymity cannot be guaranteed.
