History: In an early study of the vertebral column in the South African Bantu, Shore (1930) noted an unusual fifth thoracic vertebra in a 40-year-old Basutu male. He described the vertebral body as wedged-shaped, its anterior height reduced by approximately 6.5 mm (40%), and he felt that is clearly represented a “developmental phenomenon”. He also noted that this apparent expression of sagittal clefting was the only one observed in 1,936 Bantu vertebrae studied. An example of  sagittal clefting was reported for the skeleton of a middle-aged adult recovered from Krasnojarski Kray near the village of Podgornoe in eastern Siberia. The site is dated from the sixth to fifth centuries BC. Because its appearance resembles the wings of the butterfly, so it is called butterfly vertebrae.^[3]

Prevalence: The prevalence of butterfly vertebra in the general population is uncommon but poorly known with less than 100 case reports, yet some dedicated studies have found numbers as high as 1:5000 .^[3],[4],[5]

Etiology: unknown

Pathogenesis: It results from separate bilateral ossification center that fail to unite ^[1] which should happen around the seventh week of gestational age and end at the 25th week^[6]. Abnormal ossification of the vertebral body happens centrally, probably after incomplete fusion of two cartilaginous centers with hypoplasia at the junctional site. Butterfly vertebrae can result from a developmental abnormality leading to regression of the cauda dorsalis and formation of sagittal clefts in the vertebra into right and left halves. There are usually no symptoms. Butterfly vertebrae of normal height do not necessarily result in deviation of the spinal column axis. These most common occur in the thoracic region, but occasionally will be found in the lumber spine.^[1]

Sonographic findings: In frontal plane, we see a complete or incomplete cleft in the center of the vertebral body. Postnatally however, it is easier to confirm diagnosis by MRI.

Differential diagnosis:

• Other vertebral anomalies :

Spina bifida (posteriorly)

Block vertebra (fused vertebrae)

Hemivertebra (failure of development of one side (front/back or lateral of the vertebra)

• Other rare syndromes:^[7]

Vertical vertebral body fracture (in adult: seatbelt injury, axial loading)

Spondylothoracic dysplasia (Jacho-Levin syndrome): complex vertebral anomalies with hemi-vertebrae, rib anomalies, and absent vertebral body.

Alagille syndrome (arteriohepatic dysplasia): single or multiple butterfly vertebrae. Rickets due to hepatic disease (postnatal diagnosis).

Aicardi syndrome: butterfly vertebra and other vertebral anomalies, restricted to girls, failure to thrive, “salaam” spasms, hemihypertrophy , partly or completely missing the structure that connects the two sides of the brain (corpus callosum)

Associated anomalies: Butterfly vertebral may be associated with other congenital abnormalities such as anterior spina bifida (with or without anterior meningocele), cardiac abnormalities, forgut abnormalities and spinal diastematomyelia^[8][7], neurenteric cysts, anomalies of the lungs, gastrointestinal tract, or genitourinary tract ^[7] or a part of some rare syndromes: Pfeiffer, Jarcho-Levin, Crousen, Alagille^[9], Aicaidi syndrome ^[7], Goldenhar syndrome.^[10]

This anomaly may occur in other syndromes and also in healthy individuals. It is generally not of structural significance.^[11][5]12]

Prognosis: The prognosis is related to the presence or absence of associated anomalies. Good prgnosis with isolated butterfly veterbra^[13],[1],[5]

Management:  An isolated butterfly vertebra does not require treatment.^[2][5] The intervention only needs for associated anomalies.

References:

1. Chris J. Hutcheson, Joseph W. Howe. The low back and pelvis: clinical applications, third volume 1997 ; chapter 3, page 7.
2. Martin Weyreuther, Christoph E. Heyde, Michael Westphal, Jan Zierski, Ulrich Webe: MRI atlas:orthopedics and neurosurgery : the spine, 2007,  chapter 2, 12-16
3. Charles F. Merbs*, Sagittal Clefting of the Body and Other Vertebra. Developmental Errors in Canadian Inuit Skeletons. American Journal of physical anthropology 2004; 123:236-249
4. PaulCave: Butterfly Vertebra. British Journal of Radiology (1958) 31, 503-506
5. Suzanne B.Cassidy, Judith E.Allanson. Management of genetic syndromes. Third edition, 2010, chapter 4. 39-49
6. Keith L.Moore : The developing human:Clinally oriented embryology.Fourth edition. 1988. Chapter 15:334-348.
7. Klaus-Dietrich Ebel, Gabriele Benz-Bohm: Differential diagnosis in pediatric radiology, 1999, chapter 6, 616.
8. R Kumar, FC Guinto, Jr, JE Madewell, LE Swischuk, and R David. The Vertebral Body: Radiographic Configurations in Various Congenital and Acquired Disorders, RadioGraphics , 1988. 8: 455
9. Birkan Sonel Peyman Yalçın, Erhan Arif Öztürk, Işık Bökesoy: Butterfly vertebra: A case report, Clinical Imaging Volume 25, Issue 3 2001,  206-208
10. YK Dastur, H Trivedi, N Tapaswi, N Shah. Godenhar's syndrome with unilateral duane retraction syndrome and "butterfly" vertebra ,1985,Volume 33  Issue : 3 ,P.187-189
11. Przkora R, Schmitz A, Perlick L, Koenig R, Jaeger U, Schmitt O. Butterfly vertebrae and scoliosis: Alagille syndrome.Z Orthop Ihre Grenzgeb 2002 Mar-Apr;140(2):182-4
12. Ian D Krantz, David A Piccoli, Nancy B Spinner. Alagille syndrome. J Med Genet. 1997; 34(2): 152–157
13. Wirginia J. Maixner,Spina Bifida. Management and Outcome 2008. Chapter 14: 186-189.