Osteonecrosis of the tibia associated with imatinib in metastatic GI stromal tumor.

Case Report An abdominal mass was incidentally found by abdominal echography in a 61-year-old otherwise healthy woman during a routine physical checkup in December 2010. Subsequent abdominal computed tomography (CT) revealed a multilobulated heterogeneously enhanced mass measuring 8.2 5.6 cm in the lower abdomen with several nodules of various sizes in the peritoneum, suggesting peritoneal seeding. Multiple nodules with ring enhancement were detected in both lobes of the liver, suggesting metastasis. In addition, needle biopsy of the liver and histologic examination of the biopsied specimen revealed spindle cell tumor with positive immunostaining of CD117, confirming the diagnosis of metastatic GI stromal tumor (GIST). Tumor DNA amplified by polymerase chain reaction revealed a c-kit mutation consisting of a deletion mutation at codons 553 to 558 in exon 11. The patient received therapy with four 100-mg capsules of imatinib daily in January 2011. After 3 months of treatment, partial response was documented, as assessed by dynamic CT. At 6 months, however, the patient complained of bone pain in both lower extremities, with a limping gait and limited range of motion. A wholebody bone scan using 740 MBq (20 mCi) Tc-99m methylenediphosphonate (Siemens E-Cam Dual Head Gamma Camera, Siemens, Malvern, PA) revealed heterogeneously increased radioactivity uptake along bilateral proximal tibiae (metabolic ratio of tibia to femur, 1.56; Fig 1A), which was compatible with bone infarct. Magnetic resonance imaging was performed on a 3 T scanner (Siemens Tim Trio, Siemens) with unenhanced coronal spin-echo T1weighted images (repetition time [TR], 600 milliseconds; echo time [TE], 16 milliseconds), followed by short inversion time inversion recovery (STIR) images (TR, 6,060 milliseconds; TE, 62 milliseconds; inversion time, 150 milliseconds). STIR images revealed intramedullary heterogenous signal intensity at bilateral tibial diaphysis with serpiginous shape and abnormal enhancement suggesting osteonecrosis (ON; Fig 2A). CoronalT1-weightedmagneticresonanceimagewithfatsuppressionshowed intenseenhancementof the intramedullary lesioninbilateral tibialdiaphysis (Fig 2B). Follow-up coronal T1-weighted magnetic resonance image with fat suppression showed mild decreased enhancement of the intramedullary lesion in bilateral tibial diaphysis (Fig 2C).