Corduroy vertebra
The corduroy vertebra sign describes the appearance of thickened vertically oriented trabeculae seen in intraosseous hemangioma of the spine on lateral plain radiographs or sagittal CT of the spine (Fig. 1). The vertebral hemangioma is predominantly low in density interspersed by high density vertical striations similar in appearance to corduroy fabric [2]. This is due to the histopathologic structure of a hemangioma, which consists of thin-walled blood-filled vessels and sinuses lined with endothelium and interspersed with vertically oriented trabeculae of bone within fatty marrow [3]. On axial CT, a vertebral hemangioma exhibits a polka dot appearance due to the thickened trabeculae seen as small cross sectional areas of high attenuation surrounded by marrow fat (Fig. 1) [4].
Inverted napoleon hat
The inverted Napoleon hat sign refers to the appearance of the bicorne hat made famous by Napoleon Bonaparte in the early nineteenth century, which had a semi-circular fan-like appearance. Spondylolisthesis most commonly occurs at the lumbosacral junction, and in severe cases, the subluxed L5 vertebral body overlaps the sacrum; on the frontal view of a lumbosacral radiograph, the superimposition of L5 and the sacrum simulate the dome of the bicorne hat and the L5 transverse processes represent the hat’s tapered brim (Fig. 2) [5].
Lace-like erosions
Lace-like erosions are a radiologic manifestation of sarcoidosis caused by chronic noncaseating granulomatous inflammation of the synovium or bone, which typically affect the hands or feet. Granulomas result in punched-out cortical erosions or central lytic lesions within the medullary cavity. The characteristic appearance has been described as lacelike, latticework, or honeycombing (Fig. 3). The middle and distal phalanges are typical sites of involvement [6].
Neck tie sternum
Increased tracer uptake on bone scintigraphy within the sternum can give an appearance of a neck tie. This has been described most commonly in metabolic bone disease including renal osteodystrophy, hyperparathyroidism, and fluorosis [7, 8]. The neck tie sternum comprises expansion of the manubrium and sternal marrow without concurrent expansion of the manubriosternal joint. The latter results in a relatively narrow waist making the entire sternum appear like a neck tie (Fig. 4) [9]. The pathophysiologic basis for such an appearance is due to accelerated bone turnover and is usually accompanied by other features of metabolic bone disease including increased tracer uptake in the axial skeleton, long bones, and periarticular areas with prominent calvaria, faint visualization of the kidneys, and beading of the costochondral junctions [10].
Rugger jersey spine
This sign is pathognomonic for osteosclerosis in the thoracic and lumbar vertebrae associated with secondary hyperparathyroidism of chronic renal failure demonstrated in 27 % of patients on radiographs [11]. Sclerotic bands, representing accumulations of excess osteoid, are seen along the superior and inferior endplates with a relative band of lucency in the centre of each vertebral body, giving alternating parallel bands analogous to the stripes present on an English rugby jersey (Fig. 5) [12]. The spinal canal and intervertebral disc spaces are normal.
Absent bow tie sign of a bucket-handle tear
On sagittal MR images of the knee, a meniscus is considered normal when two consecutive images show the body of the meniscus in continuity with the anterior and posterior horns of the meniscus without evidence of a tear giving a “bow tie” appearance. When the sagittal images demonstrate only one or no body segments (“bow ties”), it is deemed positive for an absent bow tie sign and suggestive of a bucket-handle tear (Fig. 6) with confirmation being found in a displaced meniscus fragment elsewhere [13]. A bucket-handle tear, commonly involving the medial meniscus, typically consists of a vertical or oblique tear in the posterior horn that extends longitudinally through the body segment towards the anterior horn. The inner meniscal fragment is often displaced into the intercondylar notch creating the “handle”.
Extra bow tie sign of a discoid meniscus
As the name suggests, a discoid meniscus is a disc-shaped meniscus (congenital variant) with the vast majority occurring on the lateral side of the knee. The discoid shape results in greater coverage of the tibia and is usually associated with increased thickness of the meniscus that may lead to abnormal shearing forces across the knee joint predisposing to meniscal tears. The presence of a discoid meniscus is suggested on MRI when three or more 5-mm-thick consecutive sagittal images demonstrate continuity of the meniscus between the anterior and posterior horns, producing an “extra bow tie” [14].
Button sequestrum
The classic button sequestrum sign is caused by a lucent lesion with a central ossific density (Fig. 7) and can be an uncommon manifestation of osteomyelitis, eosinophilic granuloma, fibrosarcoma, and lymphoma. In osteomyelitis, an infectious organism destroys the bone, which is then replaced by purulent material and granulation tissue, thereby producing the lucent area. The central opacity represents an island of dead bone and identification of such sequestrum can be an important indication for surgery in chronic osteomyelitis [15]. Initially described on radiographs, this sign can also be observed on CT scans.
Bow tie sign of cervical spine facet dislocation
The most common orthopedic injury occurring after flexion-rotation trauma to the cervical spine is dislocation with unilateral locking of facets. Rotation of the cervical spine above the level of dislocation results in a diagnostic appearance on a true lateral radiograph. The articular facets of the vertebrae below the level of dislocation lie symmetrically parallel to each other so that only one set of superior and inferior articular facets per vertebra is visible. Above the level of dislocation, a double set of articular facets per vertebra will be present resulting in a “bow tie” appearance [16]. This is because of the rotation of the vertebrae, which now lie in an oblique position in relation to the X-ray beam.
Bow tie appearance in vertebral compression
Vertebral compression fractures are the most common type of osteoporotic fracture and are diagnosed when >20 % of vertebral height is lost on imaging. In patients with severe vertebral compression fractures of the lumbar spine, the greatest loss of height of the vertebral body occurs in the center with relative sparing of the lateral aspects. This resembles a “bow tie” appearance in the coronal plane on imaging studies [17]. This morphology of vertebral compression fracture is specific to osteoporosis and is only seen in the lumbar spine due to weight distribution through the central body of the vertebrae.