Case 46 cont'd
Then patient presented with a gradually increasing PSA level, prompting a bone scan for further evaluation.
Describe the findings in the patient’s recent bone scan, and provide your opinion:
The bony lesion of the skull is now larger but less intense, with regular borders and central photopia (as compared with intensity in the margin). This could represent a progressive mixed lytic-sclerotic bony metastasis with peripheral sclerosis.
However, the activity pattern in the skull now resembles osteoporosis circumscripta, which is most commonly associated with the Paget's disease of the skull. Therefore, Further assessment with CT of head was recommended.
The abnormal uptake in the right clavicle is slightly more extensive.
No significant interval change in radiotracer uptake of the right hemipelvis and sacrum.
Discussion:
Paget's disease of bone
Paget's disease progresses through three phases: an early resorptive phase, a mixed middle phase, and a final sclerotic phase.
Diagnosis is typically made via radiographs, which reveal lytic lesions in the early phase, and later, coarsened, expanded bone structures as the disease advances to the final phase.
The disease primarily affects osteoclasts, with subsequent increased osteoblastic activity leading to new bone formation. In the late phase, uniform sclerotic changes may develop within the affected bones. Polyostotic involvement is more common than the monostotic form.
Polyostotic involvement is more common than the monostotic form.
The duration of each phase varies and is hard to define, as phases are part of a continuous spectrum and can overlap in the same bone.
The most frequent sites of involvement are:
-
Spine (30–75%)
-
Pelvis (often asymmetric)
-
Skull (25–65%)
-
proximal long bones
Morbidity:
-
Fractures
-
Chronic Pain
-
Bone Deformity
-
Neurological complications
-
sarcomatous degeneration
Tc-99m-MDP is highly sensitive for detecting bone disease but lacks specificity. It effectively maps disease extent and distribution, showing marked uptake in all phases, except potentially normal uptake in the quiescent sclerotic phase. Notable imaging signs include the Mickey Mouse sign, where uptake in the vertebral body and posterior elements forms an inverted triangular pattern, and the Lincoln sign, characterized by diffuse mandibular uptake giving a "bearded" appearance.
radiopaedia.org
Osteoporosis Circumscripta:
"Osteoporosis circumscripta" is a radiology term used to describe Paget's disease lesions in the skull. It is a well-defined areas of radiolucency, involves the inner aspect of the outer table (stage one) and, in later stages, affects both inner and outer calvarial tables, with more extensive changes typically seen in the outer table. This is most commonly located in frontal and occipital bones
Affecting inner aspect of the outer table of the skull (stage one) and in late stages both inner and outer calvarial tables, with changes in outer table usually more extensive.
If osteoporosis circumscripta can be seen in malignancies?
Osteoporosis circumscripta is most commonly associated with Paget’s disease of the skull but can also appear in malignancies. In metastatic disease, these lesions are generally more aggressive and destructive, with irregular borders, while Paget’s disease typically presents with well-defined borders.
FDG PET-CT in Paget disease:
In early-phase Paget’s disease of the skull, FDG PET typically shows low FDG avidity. Cortical thickening and bone enlargement on CT suggest Paget’s disease, though biopsy may be needed for confirmation.
In oncology patients, a lytic skull lesion resembling osteoporosis circumscripta can be challenging to diagnose. However, normal FDG metabolism supports a benign diagnosis of Paget’s disease, potentially avoiding the need for biopsy.
Conclusion:
When interpreting osteoporosis circumscripta, careful consideration of the clinical context and additional imaging findings is essential to distinguish between Paget's disease and possible malignancies.
References:
-
Radiologic spectrum of paget disease of bone and its complications with pathologic correlation.
-
Radiographics, 22 (2002), pp. 1191-1216