Iliac Insufficiency Fracture: "Bow Sign" on Bone Scan.

Pelvic insufficiency fractures (IFs) are frequently diagnosed on technetium-99m methylene diphosphonate bone scan (BS), where it remains an important diagnostic imaging modality. Involvement of iliac bone in pelvic IFs is very rare. Differentiation from metastases is crucial where BS shows characteristic appearance obviating the need for further investigations for confirmation. There are many diagnostic appearances reported on BS for the diagnosis of IFs at various sites. We present a patient with cervical carcinoma who was previously treated with external beam radiotherapy to pelvis and now presented with pelvic pain. BS was performed to rule out skeletal metastases, however, the findings were diagnostic for iliac IF. Copyright:

A 56-year-old female, a known case of carcinoma cervix (Stage IIA), underwent radical hysterectomy and nodal dissection followed by external beam radiotherapy (EBRT) to pelvis 3 years back. The patient started complaining progressively increasing pain in the pelvis for the past 6 months. Radiograph of the pelvis at presentation showed foci of sclerosis in the iliac blades bilaterally, which was interpreted as metastatic disease. Technetium-99m methylene diphosphonate (MDP) bone scan (BS) was suggested for skeletal survey. BS showed horizontally increased MDP uptake in both iliac wings, more or less symmetrical on both sides [Figure 1]. The rest of the skeletal survey showed physiological MDP distribution in bones with no skeletal abnormality. The bilateral iliac wing uptake was considered as iliac insufficiency fractures (IFs) due to EBRT for the following two reasons: (1) symmetrical MDP uptake, which is very rare in metastases, and (2) MDP uptake conformal to the EBRT site. Subsequently, the patient was treated with bisphosphonates, calcium, and Vitamin D3 supplements with a significant reduction in pain.

Figure 1

Technetium-99m methylene diphosphonate whole-body bone scan showed symmetrically increased methylene diphosphonate uptake in both iliac wings and anterior pubic bone adjoining pubic symphysis. Correlating with a history of radiation therapy, iliac insufficiency fracture was diagnosed and called as “bow sign” seen on technetium-99m methylene diphosphonate bone scan. Diffuse physiological tracer uptake is also noted in the skull, nasal cavity, and sternum

Iliac IFs are very rare[12] and occur due to loss of elastic resistance and demineralization resulting from osteoporosis, prolonged use of corticosteroids, chronic diseases such as diabetes and renal failure, and previous radiotherapy,[34] as in our patient. It can present as diagnostic challenge in malignancy cases where it can be misdiagnosed as metastasis, especially in those malignancies that produce sclerotic metastases such as prostate, breast, carcinoid, and cervix. It is very important to be familiar with such appearance as treatment modality is totally different in benign and metastatic lesions. Many findings of IFs on BS are diagnostic[5] like “Honda sign or H-pattern” is diagnostic for sacral IF[6] and requires no further imaging for confirmation. The appearance of horizontally increased uptake in both iliac wings, giving a “bow” like appearance, is also diagnostic of iliac IF. Hence, the author would like to name it “bow sign.” Nuclear medicine physicians and radiologists should be aware of this sign to prevent iliac IF being misdiagnosed as metastatic disease.

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The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.