Incidental finding of sternal cleft on technetium-99m-methylene diphosphonate bone scan appearing as a necklace.

Sir,

A sternal cleft is a rare developmental anomaly, resulting from the failure of fusion of sternal bars which contribute to the formation of the sternum. Most cases are diagnosed in early childhood, where it is associated with serious other midline defects. A 58-year-old lady, with a history of carcinoma left breast, post modified radical mastectomy and post-chemoradiation 6–7 years ago, and on tablet letroze, presented with complains of low backache. She was subjected to technetium-99m-methylene diphosphonate (Tc-99m MDP) bone scan to rule out skeletal metastases. A whole body planar Tc-99m MDP bone scan and single photon emission computed tomography-computed tomography (SPECT-CT) of the thoracic and pelvic region was performed 3 hours after intravenous injection of 20 mCi of Tc-99m MDP on a dual head gamma camera (Infinia Hawkeye 4 SPECT/CT from GE Healthcare). The planar images of the bone scan revealed focal MDP uptake in the right lateral aspect of L5 vertebra, sacrum, right big toe and right tarsal joint [Figure 1], and a U-shaped photopenia in the region of the sternum [Figure 1]. The SPECT-CT images revealed U-shaped photopenia in the sternum corresponding to a bony cleft involving the manubrium and upper half of the sternum [Figure 2] appearing as a necklace. The Tc-99m MDP bone scan helped in diagnosing a rare congenital sternal cleft anomaly, degenerative changes in the spine, known posttraumatic changes in the right big toe with reactive changes in adjacent tarsal joints. Her chest radiogram [Figure 3] was normal. On clinical examination, there was a subtle midline bony defect in the region of the manubrium sterni with no apparent bulge or paradoxical respiratory movements.

Figure 1

Planar images of the bone scan: Focal methylene diphosphonate uptake in L5 vertebra (right lateral aspect), sacrum, right big toe, and right tarsal joint and a U-shaped photopenia in the region of the sternum

Figure 2

Single photon emission computed tomography-computed tomography images: Bony cleft involving the manubrium and upper half of the sternum

Figure 3

Chest radiogram: Normal

A sternal cleft is seen as a photopenic area on Tc-99m MDP bone scan and can cause an error in reporting the bone scan. A congenital midline cleft of the sternum is a rare developmental anomaly. It may be an isolated defect or associated with other malformations of the chest and internal organs, usually occurring as a part of a defined syndrome, for example, Cantrell's pentalogy.[1] It results from failed ventral midline fusion of the sternal bars, which normally occurs during the first 3 months of embryonic life.[12] Isolated congenital sternal cleft presents in early infancy because of cosmetic deformity, herniation of mediastinal organs and it also leads to the instability of the chest, but rarely disrupt the mechanics of breathing.

The sternum develops in the 10th week of fetal life from the consolidation of 2 bands of mesodermal cells[3] and failure of fusion of ventral midline sternal bars, which normally occurs during the first 3 months of embryonic life leads to sternal cleft.[24] The presence of these sternal bars practically determines the reconstructive surgery. The causes of this defect are unknown. This is a very rare defect with reported incidence <1% of all chest wall malformations. It may be associated with chest deformities, for example chicken breast or is an element of other malformation syndromes such as pentalogy of Cantrell (defects involving skin, sternum, diaphragm, pericardium, and heart) or the Leber syndrome (angiomas and telangiectasias)[5] or is associated with defects of great vessels (the subvalvular aortic stenosis) or it may be isolated. The detection of congenital sternal cleft, is possible in prenatal ultrasound. However, isolated sternal cleft can be unnoticed in rural areas due to unavailability of facilities and lack of awareness. That was the reason for late diagnosis in our patient who was a resident of Satpura hills of Maharashtra. The isolated congenital sternal cleft may be classified as total or partial (superior or inferior). The more common superior sternal cleft is the V-shaped one (the cleft reaches the xiphoid process) or the U-shaped one when a wide defect in the place of the sternum is closed with a distally located osseous fragment, which connects the ends of third or fourth rib on both sides.[3] The most frequently encountered form is the partial superior type, accounting for 67% of all patients, followed by the complete form (19.5%), the partial inferior form (11%), and the sternal foramen (2.5%).[5]

Our patient had an isolated partial superior sternal cleft with a U-shaped photopenic defect in the manubrium sterni on the Tc-99m MDP bone scan [Figure 1]. The definitive diagnosis of sternal cleft was established on the basis of fused thoracic SPECT-CT images [Figure 2]. Only two bone scan images have been reported so far of sternal cleft. The other differential diagnoses of photopenia in the sternum include metal attenuation artefact, sternal foramen, and osteolytic skeletal metastasis in a known case of malignancy. Hence, awareness about the sternal cleft and other differential diagnosis is necessary to avoid reporting errors.

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