Indian Journal of Nuclear Medicine

INTERESTING IMAGE
Year
: 2021  |  Volume : 36  |  Issue : 2  |  Page : 223--225

Parathyroid carcinoma – A malignant cause of metabolic skeletal super scan on fluorodeoxyglucose positron emission tomography-Computed tomography


Santhosh Sampath, Godwin Jeeva 
 Division of PET/CT, Gemini Scans, Chennai, Tamil Nadu, India

Correspondence Address:
Dr. Santhosh Sampath
Division of PET/CT, Gemini Scans, Vadapalani, Chennai - 600 026, Tamil Nadu
India

Abstract

Excessive abnormal tracer uptake in active tracer avid organ(s) with the suppression of physiological background tracer distribution is termed as super scan. Herein, we present an 18F-fluorodeoxyglucose positron emission tomography-computed tomography (FDG-PET/CT), where the metabolic pattern of skeletal super scan with coexistent parathyroid tumor was seen giving rise to the suspicion of primary hyperparathyroidism. It was subsequently diagnosed as a case of parathyroid carcinoma. Very high levels of serum parathormone in parathyroid carcinoma lead to accelerated bone turn over resulting in metabolic skeletal superscan in FDG-PET/CT which is seldom observed in parathyroid adenoma.



How to cite this article:
Sampath S, Jeeva G. Parathyroid carcinoma – A malignant cause of metabolic skeletal super scan on fluorodeoxyglucose positron emission tomography-Computed tomography.Indian J Nucl Med 2021;36:223-225


How to cite this URL:
Sampath S, Jeeva G. Parathyroid carcinoma – A malignant cause of metabolic skeletal super scan on fluorodeoxyglucose positron emission tomography-Computed tomography. Indian J Nucl Med [serial online] 2021 [cited 2021 Sep 19 ];36:223-225
Available from: https://www.ijnm.in/text.asp?2021/36/2/223/318881


Full Text



A 35-year-old male presented with diffuse body ache and unexplained weight loss. 18F-fluorodeoxyglucose positron emission tomography-computed tomography (FDG-PET/CT) scan showed extensive FDG avid (maximum standardized uptake value [SUVmax] 8.0) mixed lytic-sclerotic lesions in the skull, mandible [arrows in [Figure 1]a and [Figure 1]b], maxilla, sternum, and all the ribs [arrows in [Figure 1]c and [Figure 1]d correspond to posterior left 10th rib]. Diffuse FDG uptake was visualized in all the vertebrae showing generalized sclerosis [arrow heads in [Figure 1]c and [Figure 1]d]. Multiple small and large osteolytic FDG avid (SUVmax 8.7) and non-FDG avid [arrows in [Figure 1]e and [Figure 1]f] lesions were visualized in bilateral pelvic bones. FDG avid cortical thinning, tunneling [arrowhead in [Figure 2]a], and endosteal scalloping were visualized in the appendicular skeleton [arrows in [Figure 2]a and [Figure 2]b]. Except for the physiological uptake in the brain, there was very low background FDG distribution. These findings together with mandibular involvement [arrow in [Figure 2]c] gave rise to METABOLIC SKELETAL SUPER SCAN (MSSS) pattern that would be otherwise seen in whole body skeletal scintigraphy of metabolic bone disease.{Figure 1}{Figure 2}

A mixed solid-cystic lesion measuring 36 mm × 32 mm was seen in the posteroinferior aspect of the left lobe of thyroid [arrows in [Figure 3]a and [Figure 3]b] with very faint FDG uptake (SUVmax 2.2) in the enhancing solid components [arrows in [Figure 3]c and [Figure 3]d]. With the background of metabolic bone disease, this lesion was suggested to be a parathyroid tumor. The FDG avid lytic lesions were considered as brown tumors. Further evaluation revealed very high serum calcium (16 mg/ml) and parathormone (2831 pg/ml). The patient was subsequently treated with left inferior parathyroidectomy. The parathyroid specimen weighed 25 gram (measuring of 4.5 cm × 3.5 cm × 1.5 cm) and was diagnosed with parathyroid carcinoma due to lymphovascular invasion, stage pT1. With the absence of nonosseous lesions in the PET/CT, the stage was concluded as T1N0M0.{Figure 3}

Parathyroid carcinoma is a rare malignancy generally diagnosed after the surgery for primary hyperparathyroidism (PHPT). Those patients have significantly higher serum parathyroid hormone and calcium levels compared with other causes of PHPT.[1] Only two cases of parathyroid carcinoma presenting as MSSS in PET/CT have been reported in the literature.[2],[3] In both cases, PET/CT was done for the evaluation of recurrent parathyroid carcinoma. In our case, a provisional diagnosis of PHPT was considered based on the PET/CT findings. Marrow infiltrative disorders such as leukemia[4] and skeletal metastases from poorly differentiated solid malignancies have also been reported to cause SSS in FDG-PET/CT.[5],[6] In metastatic superscan of PET/CT, the distal appendicular skeleton is usually spared in adults due to the absence of red bone marrow, which is a prerequisite for primary hematological spread of tumor cells to the bone extracellular matrix.

In metabolic bone disease, the increased FDG uptake represents elevated metabolism associated with increased bone turn over (osteoclastic and osteoblastic activity) and hence the entire axial and appendicular skeleton show hypermetabolism. Parathyroid carcinoma is known to be poorly FDG avid.[7],[8],[9] A MSSS pattern coupled with parathyroid lesion should raise the suspicion of parathyroid carcinoma and appropriate curative treatment should be provided. Almost complete resolution of FDG uptake with improvement in cortical mineralization is observed after parathyroidectomy.[2]

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.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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