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Brown Tumour Mimicking Skeletal Metastasis in 68Ga-PSMA PET/CT
*Corresponding author: Dr. Shanmuga Sundaram Palaniswamy, Department of Nuclear Medicine and Molecular Imaging, Amrita Institute of Medical Sciences, Amrita Vishwa Vidyapeetham University, Kochi, 682041, India. ssundaram@aims.amrita.edu
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Received: ,
Accepted: ,
How to cite this article: Abhilash S, Palaniswamy S. Brown Tumour Mimicking Skeletal Metastasis in 68Ga-PSMA PET/CT. Indian J Nucl Med. doi: 10.25259/IJNM_7_2026
Abstract
We report a case of a patient with chronic kidney disease who underwent 68Ga-PSMA (prostate-specific membrane antigen) positron emission tomography/computed tomography (PET/CT) for suspected prostate carcinoma in the setting of equivocal multiparametric magnetic resonance imaging (MRI) findings, a suspicious bone lesion, and a negative prostate biopsy. Imaging demonstrated diffuse PSMA uptake in the prostate and PSMA-avid lytic lesion of the iliac bone, which was subsequently confirmed to represent a brown tumour secondary to renal osteodystrophy. This report highlights a previously unreported benign skeletal condition demonstrating PSMA uptake and mimicking metastatic disease.
Keywords
Brown tumour
Mimicking skeletal metastasis
Prostate-specific membrane antigen
Positron emission tomography (PET/CT)
INTRODUCTION
A 60-year-old man with chronic kidney disease, as part of pretransplant evaluation, underwent screening ultrasonography, which revealed bilateral contracted kidneys and prostatomegaly. Further clinical evaluation revealed lower urinary tract symptoms and an elevated serum prostate-specific antigen level of 9.14 ng/mL. Multiparametric magnetic resonance imaging (MRI) demonstrated prostate imaging reporting and data system (PI-RADS) 3 lesions within the prostate and a lytic lesion in the right iliac blade, raising concern for possible metastatic prostate carcinoma. However, subsequent sextant prostate biopsy revealed only benign prostatic tissue.
Given the equivocal MRI findings, negative biopsy, and the presence of a suspicious bone lesion, prostate-specific membrane antigen (68Ga-PSMA) PET/CT was performed. The study demonstrated diffuse PSMA uptake within the prostate gland and a PSMA-avid lytic expansile lesion in the right iliac blade, along with mildly PSMA-avid subtle sclerotic foci in the ribs and other pelvic bones [Fig 1].
CT-guided biopsy of the right iliac lesion revealed a giant cell– rich lesion without granulomas, atypia, malignancy, or fungal elements [Fig 2]. Laboratory evaluation showed markedly elevated parathyroid hormone (975.9 pg/mL; reference range, 15–65 pg/mL), normal serum corrected calcium (8.6 mg/dL; 8.6–10.2 mg/dL), high-normal serum phosphorus (4.5 mg/dL; 2.6–4.5 mg/dL) and low serum 25-OH Vitamin D level (15.54 ng/ml; >30 ng/ml). Evaluation of the CT component of the PET/CT did not demonstrate a soft-tissue lesion in the neck or mediastinum to suggest a parathyroid adenoma, nor additional generalised skeletal or extra skeletal features such as a salt-and-pepper skull, rugger-jersey spine, acro-osteolysis, or extra skeletal calcifications. These findings established the diagnosis of a brown tumour secondary to renal osteodystrophy (secondary hyperparathyroidism) rather than metastatic prostate carcinoma.
DISCUSSION
PSMA, a type II transmembrane glycoprotein, is strongly overexpressed in prostate carcinoma yet can also show variable expression in benign tissues, inflammatory states, and tumour-associated neovasculature.[1] Bone is the most common site of hematogenous metastasis in prostate carcinoma, typically showing osteoblastic lesions; however, osteolytic or mixed patterns are occasionally encountered.[2,3]
Benign and malignant skeletal disorders such as Paget disease, haemangioma, fibrous dysplasia, multiple myeloma, etc., have been reported to show PSMA uptake on PET imaging.[4] Brown tumours are skeletal manifestations of hyperparathyroidism and typically present as well-defined osteolytic, expansile lesions, sometimes associated with cortical destruction or pathologic fractures. Depending on disease stage, lesions may show mixed lytic–sclerotic patterns, ill-defined margins, or adjacent soft-tissue components.[5,6]
A prior case report described a brown tumour mimicking skeletal metastasis on bone scintigraphy in a patient with primary hyperparathyroidism.[7] To our knowledge, the present case represents the first report of a brown tumour demonstrating PSMA expression on PET imaging, thereby mimicking skeletal metastasis.
Author contribution:
SA: Writing the case report manuscript and editing the images; SSP : Providing critical feedback and correcting the manuscript.
Ethical approval:
Institutional Review Board approval is not required.
Declaration of patient consent:
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given consent for their images and other clinical information to be reported in the journal. The patient understand that the patient’s names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Conflicts of interest:
There are no conflicts of interest.
Use of artificial intelligence (AI)-assisted technology for manuscript preparation:
The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.
Financial support and sponsorship: Nil
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