bone scintigraphy is an important modality for the examination of various pathological conditions of the skeletal system .
radionuclide bone imaging is quick , relatively inexpensive , widely available , and exquisitely sensitive and is invaluable in the diagnostic evaluation of numerous pathological conditions .
these compounds accumulate rapidly in bone , and by 2 - 6 h after injection , about 50% of the injected dose is in the skeletal system .
tc - methylene diphosphonate ( tc - mdp ) imaging , customarily directed toward identifying altered skeletal metabolism , has been used extensively to image a variety of extraosseous lesions , especially heterotopic ossification and metabolic , metastatic calcification .
we report a rare case of accumulation of bone scintigraphy tracer in a phlebolith in a patient of adenocarcinoma of lung .
a 43-year - old female patient , known case of adenocarcinoma of right lung was referred for a tc - mdp bone scan with complaint of persistent low backache since 3 months .
the scan showed abnormal , focal increased tracer uptake in left pelvic cavity , not localizing to any bone of the skeleton [ figures 1a and b , arrows ] .
the uptake was persistent even in post - void imaging done after adequate hydration , giving us a clue that it was not due to tracer hold up in the ureter . on single photon emission computed tomography and computed tomography ( spect - ct ) imaging ,
the focal tracer uptake localized to a small focus of calcification in the left pelvic cavity away from the ureter [ figure 2 , arrow ] .
an additional ultrasonography of the pelvis confirmed that there was no ureteric calculus [ figure 3 ] .
review of the patient 's recent contrast - enhanced computed tomography revealed a phlebolith in left iliac vein ( ct hounsfield unit : 338 ) .
thus , we concluded the extraosseous tc - mdp uptake was due to phlebolith in the left iliac vein .
planar bone scan ( a and b ) of a 43-year - old female patient , a known case of adenocarcinoma of right lung .
focal , intense tracer uptake seen in left pelvic cavity ( arrow ) correlative single photon emission computed tomography and computed tomography fusion imaging localized this uptake to a phlebolith in left iliac vein ( arrow ) ultrasonography of the pelvis showing ureteric jets bilaterally ( arrows ) , ruling out obstruction ( calculus ) in the ureter
tc - mdp , a bone scan tracer , has rapid blood clearance , excellent in vivo chemical stability , and a high bone - to - soft tissue ratio , which are ideal for bone imaging .
although tc - mdp is customarily used to evaluate skeletal pathological conditions , its excellent clearance from normal soft tissues allows the detection of abnormal extraskeletal tc - mdp accumulation .
it is hypothesized that tc - mdp and its analogues bind to bone by adsorption to the surface of the hydroxyapatite crystal . while in soft tissue ,
these pathways result in uptake of tc - mdp through what is believed to be chemisorption of the radiopharmaceutical onto the surface of the calcium salts .
phleboliths are deposits which develop in the wall of a vein and are composed of calcium or lime .
these are most commonly seen in the lower pelvis and sometime occur in large numbers .
they are often confused with ureteric stones when seen around the urinary bladder in the pelvic cavity . however
, on plain radiographs , these can be distinguished from a calculus due to the presence of a translucent center and circular or oval shape.[810 ] bone scan tracer uptake in a phlebolith has been described in past .
dystrophic calcification occurs in patients with normal ca + and po4 levels and refers to ca + deposition in tissues secondary to histological disruption caused by trauma , ischemia , or cellular necrosis or in the enzymatic necrosis of fat .
it is thought that calcium ion binds to phospholipids present in membrane bound vesicles , phosphatases generate phosphate groups which in turn bind to the calcium , and the cycle is repeated until local concentrations are elevated and crystals begin to form .
hyaline collagen degeneration , a consequence of tissue damage , is particularly associated with ca + deposition .
similar mechanism operates in other known causes of extraskeletal bone scan tracer uptake in tissue infarction , deep vein thrombosis , scars , and dermatomyositis . to conclude
, we report a rare case of extraosseous uptake of bone scan tracer in a phlebolith . with growing use of integration of ct with spect
, nuclear medicine physicians should become aware of such anatomical changes and variants so as to avoid misinterpretation .
the awareness of the underlying pathophysiological basis of these changes and uptake of mdp in extraosseous soft tissue can significantly enhance the interpretation and diagnostic value of bone scintigraphy .
 uptake in non - osseous , non - urologic tissues is occasionally found in the performance of bone scintigraphy . 
 these uptakes reflect an atypical interaction between the radiopharmaceutical and the patient . 
 knowledge of the rare extraskeletal uptakes and their clinical relevance helps in better interpretation of bone scans . 
 we report an unusual occurrence of extraosseous accumulation of 99mtc - methylene diphosphonate in a phlebolith in bone scan , confirmed with the aid of photon emission computed tomography and computed tomography . 