Symbia T16 SPECT•CT Characterization and Guided Biopsy in a Case of Benign Bone Tumor

Symbia SPECT and CT data critical for appropriate diagnosis

William Pavlosky, MD

Case study data provided by Timmins and District Hospital, Timmins, Ontario, Canada


 |  Oct 25, 2012

History

A 36-year-old female patient presented with history of pain in the right thigh usually at night, which has been progressing for past 6 weeks. There was no history of trauma. The patient had history of Hashimoto’s thyroiditis and was treated with thyroxine. Initial plain radiograph showed a lucent lesion in the middle of right femoral shaft, with endosteal scalloping and minor bone expansion. Erosion of the inner margin of the cortical bone suggests an expansile soft-tissue lesion. The patient underwent 99mTc MDP whole-body bone scan combined with SPECT•CT of the femoral shaft region.

 

Diagnosis

Study was performed on Symbia™ T16 with integrated thin-slice diagnostic CT performed prior to SPECT study. CT data was used for attenuation correction of SPECT. The patient was referred for bone biopsy and curettage. Biopsy was guided by SPECT•CT findings and was taken from the area corresponding to the hypermetabolic focal uptake in the marrow cavity of the right femur seen on SPECT with the integrated CT helping correct localization. Histopathology report of the biopsy specimen was diagnostic for fibrous dysplasia. The patient was symptom-free for a few weeks following biopsy and curettage, but returned with new bone pain. Although the tumor was well-delineated with MRI (Fig 1) and the extent of the inner cortical erosion defined by CT, it was difficult to identify the proper area to take a biopsy from in a CT-guided biopsy. MRI showed a variegated appearance, but correlation with high-quality Symbia SPECT•CT (Fig 4) confirmed the fact that the enhancing part of the tumor also was the most metabolically active and the right area to source the biopsy specimen.

 

Fig. 1: MRI shows a space occupying lesion with variegated components. A large part of the lesion demonstrates a multiloculated cystic component on STIR imaging with enhancement within the lesion restricted to a solid posterior component that was hypointense on all pre-contrast imaging se-quences. Slight periosteal edema and enhancement is visualized along with slight erosion of the inner margins of the cortex in the affected area. Marrow edema proximal and distal to the lesion also is seen to enhance.

 

Fig. 2: The CT study shows erosion of the inner margin of the cortex of the middle part of shaft of right femur correlating with the MRI findings. The endosteal scalloping and cortical thinning is well delineated.

 

Fig. 3: Post-biopsy radiograph shows opacity within the shaft related to post-biopsy filling of the tumor cavity with methacrylate.

 

Fig. 4: SPECT•CT study shows focal increase in skeletal metabolism in the posterior aspect of the lesion corresponding to the region of contrast enhancement and presence of solid component seen on MRI. The cystic component demonstrated on MRI was not metabolically active. Faint uptake of MDP also was seen in the marrow proximal and distal to the lesion corresponding exactly to the findings on MRI. Integrated diagnostic CT correlates with findings seen on previously performed CT and helps define the exact position of the hypermetabolic area. The whole-body MDP imaging demonstrated that the femoral lesion was an isolated finding with no other demonstrable sites of hypermetabolic activity.

 

Discussion

The integrated thin-slice diagnostic CT performed as a part of the SPECT•CT procedure provided the localizing landmark for the CT-guided biopsy procedure to hit the most metabolically active area of the tumor delineated by SPECT, which yielded the most dependable biopsy result. Patient was subsequently treated with open, complete removal of tumor with intramedullary rod stabilization. Subsequent to surgery, patient remains symptom-free.

Fibrous dysplasia is a skeletal develop-mental anomaly of the bone-forming mesenchyme that manifests as a defect in osteoblastic differentiation and maturation. It involves replacement of medullary bone with fibrous tissue causing expansion of bone and erosion of cortical bone. Most lesions are single, although multiple lesions are occasionally seen (polyostotic fibrous dysplasia). The skull and facial bones are common sites. There are incidental reports of use of SPECT•CT in fibrous dysplasia. Zhao et al (Clin Nucl Med. 2009 Dec; 34(12):898-901.) published a case report of fibrous dysplasia of L3 vertebrae with SPECT•CT and MRI combined for diagnosis. Increased uptake of 99mTc MDP in bone scintigraphy is a hallmark of fibrous dysplasia related to the metabolic activity of the involved medullary bone. However, focal areas of increased skeletal metabo-lism do not show corresponding increase in glucose metabolism of Fludeoxyglucose F 18 injection* PET (Toba et al Ann Nucl Med. 1998 Jun; 12(3):153-5).

 

Conclusion

Symbia high-resolution SPECT•CT-guided biopsy to reach the most metabolically active part of the tumor was instrumental in proper histopathological evaluation of the lesion. In view of the variegated appearance in MRI, the integrated Symbia SPECT and CT information, which helped guide the biopsy procedure, was critical for appropriate diagnosis and management decision making.