Case Author(s): Lisa Oakley, M.D. and Jerold Wallis, M.D. , 10/17/97 . Rating: #D2, #Q3

Diagnosis: Giant Cell Tumor of Sacrum

Brief history:

15-year-old girl with buttock pain.

Images:

Anterior and posterior delayed whole body bone images

View main image(bs) in a separate image viewer

View second image(bs). Additional spot images (post-void images of the pelvis)

View third image(ct). Once you have decided on the region of bony abnormality, view this CT image for correlation.

Full history/Diagnosis is available below

Diagnosis: Giant Cell Tumor of Sacrum

Full history:

15-year-old girl who presented to an outside hospital 7 months previously with complaints of buttock pain. Bone scintigraphy was performed at that time and was read as negative. The patient continued to complain of buttock pain and repeat bone scintigraphy was performed.

Radiopharmaceutical:

Tc-99m MDP

Findings:

Bone scintigraphy shows a relatively large area of decreased uptake in the body of the sacrum. Mildly increased activity is noted in the sacrum adjacent to the region of decreased uptake.

The CT scan shows an expansile 6-cm soft tissue mass arising from the left sacrum. The mass obliterates the left sacral neural foramina and appears to break through sacral cortex, extending into the posterior pelvis.

Discussion:

Giant cell tumors (GCTs) represent about 4% of all primary bone tumors, but less than 2% are seen in children less than 15 years of age. These tumors are often expansile and very vascular, containing osteoclast-like multinucleated giant cells. They can arise anywhere in the skeleton, but the most common sites are the distal femur, proximal tibia, and distal radius. The scintigraphic appearance is fairly characteristic, although nonspecific, with more than half demonstating a "donut sign"--i.e., a central region of decreased activity corresponding to the tumor mass surrounded by a thick rim of intensely increased uptake due to marginal reactive new bone formation. In other instances, the tumor may appear purely "hot" or "cold".

"Cold defects" are often due to lytic tumors that do not incite significant reactive osteoblastic activity or to tumors (or other processes) that completely replace the bone marrow (and thus interfere with the blood supply to the bone). This appearance, though relatively uncommon, has been described in a wide variety of primary bone tumors and in metastases. At least 2% of metastatic lesions demonstrate decreased activity on bone scintigraphy and, although this finding is particularly common in multiple myeloma and renal cell carcinoma, one will encounter this appearance more frequently in association with breast and lung carcinoma given their overall greater incidence. Lesions of multiple myeloma, given their small size, may not be apparent on bone scintigraphy when they have decreased uptake.

This case is somewhat unusual due to the relatively young age of the patient, although GCT is certainly a consideration given the appearance and location of this tumor.

Reference: Skeletal Nuclear Medicine, B. David Collier, Ignac Fogelman, and Leonard Rosenthall, 1996

Followup:

Follow up biopsy of the mass revealed a giant cell tumor.

In retrospect, the original bone scintigraphy study performed 7 months previously was subtly positive (please see follow up image). There is a small region of decreased uptake in the left sacrum. The interval change since the prior exam highlights the degree of bony destruction in the sacrum.

View followup image(bs). Posterior view of the pelvis (original bone scintigraphy)

Major teaching point(s):

Areas of decreased activity are often more difficult to identify than areas of increased uptake.

Differential Diagnosis List

Metastasis or other primary tumor

Sacral osteomyelitis with bony destruction (in the setting of a decubitus ulcer)

Osteoradionecrosis (following radiation therapy)

ACR Codes and Keywords:

References and General Discussion of Bone Scintigraphy (Anatomic field:Spine and Contents, Category:Neoplasm, Neoplastic-like condition)

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Case number: bs085

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