CASE 12
By: Dr. Saleh Othman, MD, MSc, JMCB
HISTORY: 67-year-old male with prostate cancer with right lower limb pain. PSA=97.
What are your findings?
What is your impression?
What are the pathophysioloy of the disease?
FINDINGS:
Tc-99m MDP total body bones scan shows multiple focal areas of increased uptake seen at skull, spine, ribs, sternum, iliac bones, sacrum, shoulders and proximal femoral.
DIAGNOSIS:
Bone metastases.
PEARLS AND DISCUSSION:
Non-osseous tumors have access to the bone by three routs: direct Extension, retrograde venous flow and arterial Circulation (after venous or lymphatic access).
Epithelial tumors reach red marrow of axial skeleton via venous and arterial flow. The red marrow in adult is distributed in calvarium, spine, pelvis, and proximal femurs and humerus. That explains why 90% of metastasis from epithelial tumors metastasize to these areas.
The metastatic focus grows in red marrow space. The surrounding bone remodels through osteoclastic (resorption) and osteoblastic (deposition) activity. The relative balance between resorption and deposition determine whether the lesion is hot (sclerotic), cold (lytic) or mixed pattern. The tracer does not concentrate in the metastatic focus (cancerous tissue) but in the surrounding reactive bone. Tumors with sclerotic or mixed reaction can give different patterns ranging from solitary lesion, multiple lesions or superscan pattern. On the other hand, purely, lytic lesions commonly give normal (false negative) appearance.
Solitary lesions can be benign or malignant (Fig. 1) and that will be further clarified with correlation with radiograph, CT and biopsy if needed. The location and pattern of the lesion will favor its nature, anterior rib ends rarely represent metastases and mostly traumatic while vertebral solitary lesion has 40-80% chance to be malignant. The most common causes of benign solitary lesion: osteomyelitis, frontal osteoma, trauma, monostotic Pagets disease, enchondroma and fibrous dysplasia.
In multifocal lesions the pattern of distribution is a key feature in differentiating metastatic from non-metastatic lesions such as arthritis, trauma and insufficiency fractures in osteoporosis, Paget’s disease, metabolic bone disease, multi focal osteomyelitis, infarctions, etc.
The third pattern is the diffuse involvement of the skeleton “the super scan” which has been defined as bone scan with diffuse symmetrical increased uptake and almost absence of soft tissue activity, lack of kidney activity and bone uptake seen in blood pool images (Fig. 2). The super scan is caused by malignant metastatic disease from different tumor such as prostate, breast, lung, bladder and lymphoma or from benign conditions such as hyperparathyroidism, osteomalacia, Paget’s disease and fibrous dysplasia. There are important clues to differentiate between the two entities: In metabolic bone disease the calvarium and long bones are involved unlike in bone metastases where they are usually spared.
Teaching Points:
In early stage of the tumor bone scan superior to x-ray. While in advanced stage both have high sensitivity.
The scan may have different patterns: Solitary or multiple focal lesions, diffuse involvement (Superscan), photon deficient lesions (cold lesions), flare phenomenon, normal (false negative) or soft tissue lesions (tracer uptake in tumor).
The sensitivity is agreed to be 90% or more.
FURTHER READING:
Radiol Clin North Am 1993; Brown ML. Bone scintigraphy in benign and malignant tumors. 31(4):731-8. Review.
J Nucl Med 2005; Even-Sapir E. Imaging of malignant bone involvement by morphologic, scintigraphic, and hybrid modalities. 46: 1356-1367
