Osteology Case 10

Osteology Case 10

Dr. Sharjeel Usmani

Consultant Nuclear Medicine
Sultan Qaboos Comprehensive Cancer Care and Research Center
(SQCCCRC), Muscat Oman
54-year old female is a known case of breast cancer on hormonal therapy referred for 18F-NaF-PET/CT due to generalized bone pain and rising tumor marker. 18F-NaF-PET/CT performed after injection of 4.6mCi18F-NaF for restaging. a) MIP 18F-NaFimage demonstrate degenerative/arthritic changes with increase osteoblastic activity at right 7th costochondral junction (osteochondritis) and facets joints of C3-C5 vertebrae (degenerative changes)b) Incidental 18F-NaF uptake is seen at right parietal region of skull (black arrow).c) Non-contrast CT images show sclerotic lesion at right parietal with corresponding increased tracer activity on fused images (white arrow). Solitary osteoblastic lesion at right parietal region with sclerotic changes on CT.

What is the diagnosis ?

a) Non-aggressive bone lesion at right parietal bone, likely enchondroma or fibrous dysplasia; for follow-up.

b) 18F-NaF uptake is likely in the calcified brain metastasis at parietal lobe of the brain. Advised MRI for confirmation.

c) Aggressive fusiform solitary osteoblastic bone lesion at right parietal bone is highly suspicious for bone secondaries; for further radiological evaluation.

d) 18F-NaF uptake is likely in the calcified meningeal lesion at parietal region of the brain is likely due to meningioma. Advised MRI for confirmation.

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Answer: d

d) Meningioma

Non-contrast CT images showbroad-based calcified mass attached to the right parietal bonewith increased thickening of inner table of right parietal bone, massshowincrease tracer uptake on fused images. Meningioma was suspected. MRI and follow-up scan is advised.

Meningiomas are the most common duraltumourarise from the meningothelial cells of the arachnoid membranes, which are attached to the inner layer of the dura mater [1].It usually seen as an incidental finding on brain imaging and represent about 20% of all intracranial tumors. It is important to differentiate it from other mimics like primary neoplastic processes, metastases, granulomatous diseases and infection.

Meningiomas typically appear as lobular, extra-axial masses with a broad dural base. Typical features on unenhanced CT images are well-circumscribed, smoothly marginated extra-axial mass abutting the dura. Approximately 70-75% of meningiomas are hyperattenuating to surrounding brain parenchyma, while roughly 25% are isodense. Calcification is seen in approximately 20-25% of cases [2,3].

MRI is the modality of choice for evaluating meningiomas due to superior contrast and has ability to differentiate between intra- and extra-axial lesions. The typical MRI characteristically demonstrate, iso- to hypointensity on T1-weighted, and iso- to hyperintensity on T2-weighted images. Typically, meningiomas demonstrate homogeneous enhancement after contrast injection. however, the areas of central necrosis or calcification that do not enhance [4].

Meningiomas can be identified incidentally on bone scans likely because of calcification which thought to be seen in 25% of the meningiomas, other localization factors are presence/absence of a vascular pool [5]. Few case reports of 18F-NaF PET/CT also shows localization of 18F-NaF in meningiomas [6,7].Like conventional bone scintigraphy with 99mTc-MDP, 18F-NaF also accumulates in extra osseous lesions due calcification or calcifications within necrosis [8]. The mechanism of 18F-NaF uptake in calcified lesions is its direct incorporation into the hydroxyapatite crystal. 18F-NaF can accumulate in intracranial lesions due to both benign and malignant etiologies which include brain stroke, tumors, and metastatic lesions [9]. Clinical information and morphological information from correlative CT are essential for a correct diagnosis.


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