An uncommon case showing three different pathologies on (99m)technetium-methylene diphosphonate bone scintigraphy.

(99m)Technetium-methylene diphosphonate bone scintigraphy (BS) has an important role in evaluating skeletal pathology, especially its extent. Incidental extra-osseous uptake may sometimes be seen in soft-tissue pathologies. We present a 64-year-old female with skull base osteomyelitis referred for BS which revealed involvement of the skull base on the left side, uptake was also noted in bilateral lungs secondary to hypercalcemia of renal failure and in the D12-L1 vertebrae as the patient had a history of Pott's spine. This is perhaps a unique case showing three findings each of a different etiology in the same scan.

A 64-year-old female was referred to our department for a three phase 99mtechnetium (99mTc)-methylene diphosphonate bone scintigraphy (BS) for evaluation of skull base osteomyelitis. Co-morbidities included diabetes mellitus and renal failure. Planar BS was equivocal in showing mildly increased uptake on the skull base left side [Figure 1a, dotted arrow] which when corroborated with single photon emission computed tomography/computed tomography (SPECT/CT) revealed involvement of the left mastoid [Figure 1b–d, arrow] and petrous temporal thus confirming skull base osteomyelitis. SPECT/CT had an incremental value over planar imaging in evaluating the bones involved. Diffuse radiotracer uptake was also noted in bilateral lung fields [Figure 1a, thin arrows] along with another area of increased uptake in dorso (D12) - lumbar (L1) spine [Figure 1a, thick arrow]. Her serum urea was 74 mmol/l; serum creatinine - 2.4 mmol/l; serum calcium - 13 mg/dl; serum phosphate - 7.0 mg/dl and alkaline phosphatase - 247 IU/l, thus confirming lung uptake secondary to hypercalcemia of renal failure. The patient had a history of Pott's spine 2 years ago for which she had taken antitubercular treatment followed by pedicle screw fixation of D12-L1 vertebrae. So BS basically revealed all three aspects of disease pathology in the same scan.

Figure 1

99mTechnetium-methylene diphosphonate bone scan planar (a) and Single photon emission tomography (SPECT) (b), computed tomography (CT) (c) and hybrid SPECT/CT (d) images. SPECT/CT showed an incremental value over planar imaging in diagnosis of skull base osteomyelitis (a, dotted arrow; b-d, arrow). Also diffuse radiotracer uptake was noted in bilateral lung fields (a, thin arrows) due to hypercalcaemia, along with another focal area of increased uptake in lower dorso (D12) - lumbar (L1) spine region (a, thick arrow) due to Pott's spine

A positive uptake on a 99mTc-MDP or gallium-67 scan is said to be diagnostic of skull base osteomyelitis in the appropriate clinical scenario.[1] SPECT/CT has been found to be useful for the diagnosis of skull base osteomyelitis.[2] Radioisotope scans are also useful for follow-up and treatment monitoring.[3] Lung is the most common site of metastatic calcification as relatively low carbon dioxide tension of the extra-cellular fluid surrounding the alveoli causes an alkaline environment that favors the deposition of calcium.[4] Metastatic calcium deposition has been reported in hyperparathyroidism, parathyroid carcinoma, chronic renal failure among other diseases associated with a calcium-phosphate ion-product >5 mmol2/l2.[5] Extra-osseous calcium deposition has also been reported in kidney and stomach.[6] BS has emerged as an important tool in the diagnosis and management of Pott's spine[7] with sensitivity approaching 75%.[8] To our knowledge this is a unique case in literature showing three different findings from different etiologies in the same BS.