Is femoral uptake of Tc99m-methylene diphosphonate on bone scintigraphy in bronchogenic carcinoma an alarming sign: A case report and brief review of literature?

Detection of skeletal metastasis in patients with lung cancer is important from management point of view. We report the bone scan finding in a patient with non-small cell lung carcinoma showing isolated abnormal tracer in femur and having a characteristic appearance in computed tomography, highlighting the importance of bone scan in patients with bronchogenic carcinoma.

INTRODUCTION

Lung cancer is the leading cause of cancer-related mortality in both men and women throughout the world. It is also the most commonly diagnosed cancer worldwide with most of them at an advanced stage with a poor prognosis. Presence of skeletal metastasis renders a patient clinically inoperable. Whole body bone scan is useful in detecting asymptomatic bone metastases. Review of literature shows characteristic pattern of metastatic bone involvement in bronchogenic carcinoma.

CASE REPORT

A 78-year-old male smoker patient diagnosed to have non-small cell lung cancer (NSCLC), stage IV (adrenal and liver metastasis) was subjected to whole body bone scan to detect skeletal metastases, if any. The patient had received local palliative radiotherapy 20 Gy/5# for 1 week and was on chemotherapy with gefitinib since 12 days. There was no history of bone pain or skeletal trauma. Bone scintigraphy was performed 3 h after intravenous injection of Tc99m-methylene diphosphonate. Increase in tracer uptake was noticed in the lower cervical vertebrae, right first rib, and medial cortical margin of the lower third of shaft of left femur [Figure 1a and b]. Hybrid single photon emission computed tomography/computed tomography (CT) localized the cervical uptake to left articular process of C6 and left transverse process of C7 vertebrae with dense sclerotic changes likely degeneration due to altered weight distribution.

Figure 1

Tc99m-methylene diphosphonate whole body bone scan in (a) Anterior projection (b) Posterior projection showing abnormal tracer uptake in the lower third of shaft of left femur (arrow). Hybrid single photon emission computed tomography/computed tomography (CT) localized the CT images (c and d) of the lower third of the left femur showed lysis of the anteromedial cortical margin (arrow)

CT scan of the lower third of the left femur showed lysis of the anteromedial cortical margin with no soft tissue component [Figure 1c and d]. On the basis of bone scan and pattern of cortical bone destruction, the diagnosis of a skeletal metastasis from a bronchogenic carcinoma was suggested.

DISCUSSION

Incidence of bone metastases in cancers of the breast, prostate, lung and kidney, is very high, approximately 70% of all patients.[1] The reported incidence of bone metastasis from NSCLC is around 15%-40%, most of which involves spine, rib, and pelvis and 6% in femur.[2] No effective treatment is available at the moment for bone metastases. Bronchogenic carcinoma is an established entity in causing cortical bone metastases[34] Literature review also shows primaries in lung, breast, kidney, and pancreas as causes of cortical metastasis.[5] Of particular interest is the involvement of femur with studies reporting osteolytic cortical lesions preferentially located at the femur as typical of bronchogenic carcinoma.[34] The reason for this special predilection for implantation in the cortical bone, particularly the femur, is still unknown. It is speculated that the vascular network, originating in the overlying periosteum of the long bones, serves as a pathway for metastatic deposits to destruct the cortical bone. Literature review not only shows predominance of femoral involvement in bronchogenic carcinoma, but also patients with only pure cortical metastases had exclusive femoral involvement.[6]

Four distinctive patterns of bone destruction in bronchogenic carcinoma have been described. A small focal intra-cortical lesions (“cookie-bite” or “cookie-cutter” pattern); large osteolytic lesions; saucerized intra-cortical lesions with well defined periosteal reaction; and lesions with predominant cortical destruction extending into the soft tissue as well as the medullary cavity.[7]

The term “cookie bite metastasis” was initially coined for a small intra-cortical lesion. Although these lesions are not entirely pathognomonic, literature review shows that such lesion within the skeleton as initial diagnosis should alert the radiologist to the possibility of a primary neoplasm of the lung.[7] These are considered highly typical of metastasis from bronchogenic carcinoma.[45]

Our case further illustrates how a high degree of suspicion is needed in interpreting isolated uptake in bones scan in the femur in patients with bronchogenic carcinoma. Moreover, as described in literature, the characteristic pattern of cortical destruction if found in a patient with carcinoma of unknown primary, then the search for an occult primary neoplasm should be started without delay.