Atlanto - Occipital Fusion - Report Of Two Cases
Author(s): Jayanthi V., Kulkarni, R.; Kulkarni, R.N.
Vol. 52, No. 1 (2003-01 - 2003-12)
Department of Anatomy, M.S. Ramaiah Medical College, Bangalore- INDIA.
Abstract
Skeletal abnormalities at the craniocervical junction may result in sudden unexpected death. We report two skulls
showing occipitalization of the atlas. Of the two skulls, one skull showed defect in ossification called "Spina-Bifida-Posterior". The fortuitous
discovery of this skull with defects in ossification especially of the atlas prompted us to review the literature particularly on this
developmental anomaly. Posterior-Spina-Bifida involves 3% of all the spines examined. Anterior and posterior foramen magnum dimensions
were remarkably narrowed.
Key words: Atlas, Foramen Magnum, Anterior Arch, Posterior Arch, Occipital Bone.
Introduction:
Craniovertebral abnormalities have been
recorded for many years in morphological and
clinicoradiological studies.
Occipitalization of the atlas, assimilation of
atlas or atlanto-occipital fusion is one of the common
skeletal abnormalities of the upper cervical spine.
Hypoplasia of the basiocciput can be found in
manifestations of the occipital vertebra, in atlas
assimilation and in atlantooccipital fusion. These
patients with craniovertebral joint anomalies exhibit
the first neurological signs and symptoms usually no
sooner than the second decade (Kruyff ; 1965).
Anomalies in the region of the foramen
magnum were of the interest mainly to anatomists.
(McRae & Bernon, 1953). These began to be
described in pathological literature only in the later
half of the 19th century.
Review of Literature:
Atlantooccipital fusion or occipitalization of
atlas or assimilation of atlas has been extensively
dealt with in the literature by craniologists. There are
previous reports of both ossification defects and
atlanto occipital fusion. Our study is compared with
previous workers. These earlier reports are
summarized below.
Table-1 Symptomatology of Atlanto-Occipital fusion.
Sr. No.
Author
Year
Symptoms
1.
Kussmaul & Tenner
1859
Convulsions in all 3 reported cases
2.
Englander
1934
Cervical pain
3.
Hadlay
1948
Neurological Symptoms.
4.
Keller
1961
Seizure disorder
5.
Lopez Zanon et al
1964
Cervical Pain in all 3 reported cases with tonic clonic convulsions in two out of them
6.
Budin & Sondheimer
1966
Cervical pain following hyperextension and Onset of cervical pain while putting sweater
7.
Albert & Castrischer
1968
Cervical Pain.
8.
Childers & Wilson
1971
Pain in the neck in some of 25 reported cases; others being either asymptomatic or having insufficient clinical data
9.
Vakili et al
1985
Sudden death.
Case Report:
In our study related to foramen magnum we
noticed two skulls each showing occipitalization of
atlas. These were labelled I and II.
Skull I: Showed atlanto occipital fusion with
associated spina bifida posterior of the atlas. This
skull showed complete fusion of only one of the
transverse processes with the occipital bone. The anterior arch of this atlas was incompletely fused
with occipital bone (fig. 1).
Skull II: In this skull the anterior arch of atlas
was fused with the occipital bone. This skull also
showed fiusion of only one of the transverse
processes of atlas to the occipital bone. One half of
the posterior arch was fused with the occipital bone
and the other half of the posterior arch was probably
broken (fig. 2).
Embryology:
In some lower vertebrates (e.g.: Reptiles ) the
cranial half of the first cervical sclerotome remains
as a separate bone 'the proatlas' between the
occiput and C1 vertebra. In man it becomes
assimilated into the occipital condyles and also
forms the tip of the dens. The caudal half of first
cervical sclerotome gives rise to the lateral masses
and the anterior and posterior arches of C1 vertebra.
The body of C1 vertebra disappears early giving rise
to all but the tip of the dens. The body, posterior
arch and transverse process of C2 vertebra is
derived from second cervial sclerotome. If the
normal segmentation fails to occur, atlantooccipital
fusion results. (Shipro & Robinson, 1976). The
single anterior ossification of the first cervical
vertebra is well described in the classic study of
Macalister; 1893. According to him, "Two
ossification centres appear, one just posterior to
each of the lateral mass and transverse process".
The two ossification centres meet in the middle,
posteriorly usually by late in the fourth year of life.
At about six months of age ossification begins in the
anterior part of atlas generally by two closely
approximated ossification centres, which usually
unite within a few months of their apearance.
Ocasionally there may be single anterior ossification
centre. Ossification proceeds posterolaterally along
both anterior and fusion to the lateral masses takes
place in the fifth year of life (Macalister, (1893).
A midline defect can result from the failure of
fusion of the ossification centres either anteriorly or
posteriorly.
Discussion:
Neurological symptoms associated with
occipitalization of the atlas are attributed to the
ligamentous laxity of the transverse ligament about the odontoid process caused by repeated flexion
and extension of the neck leading to the
compression of the spinal cord or actual indentation
of the medulla oblongata.
With aging, the central nervous system may
be less tolerant to repeated blows from the odontoid.
As per McRae's & Barnon (1953) study in 25
patients, they noticed 2 fusions of C2 and C3
vertebrae. The patient will be probably
asymptomatic if the odontoid process is located
below the level of foramen magnum. This
relationship is best assessed through the use of
McRaes & Barnon (1953) line which is drawn across
the foramen magnum. Normally the odontoid
process should not project above this line.
According to Greenberg (1968) spinal cord
compression always occurs when the sagittal spinal
canal diameter behind the odontoid process is less
than or equal to 14 mm. Cord compression is
possible when the sagittal canal diameter is between
15 and 17 mm. And almost never occurs at a
distance of 18 mm or more.
According to McRae & Barnon (1953), patients
with occipitalization of the atlas may have the
following physical features: low hairline, torticollis,
restricted neck movements and / or abnormal short
neck. In neurological examination of the atlanto
occipital fusion patient may reveal the following
clinical findings: headache, neck pain, numbness
and pain in the limbs, weakness, abnormal head
posture, posteriorly located dull aching headache.
Cranial nerve findings associated with
occipitalization of the atlas include tinnitus, visual
disturbances and lower cranial nerve palsies leading
to dysphagia and dysarthria. The neurological
symptoms and signs of atlanto-occipital fusion can
not be distinguished from those of the Arnold Chiari
malformation as the pathophysiology of both is
essentially the same.
Fusion between atlas and occiput occurs
anteriorly between the arch and rim of the foramen
with some segment of the posterior arch of C1
present in some instances. This fragment can
frequently constrict the spinal canal causing
intermittent symptoms depending on the position of
the head. (Bailay et al, 1983).
Conclusion:
Atlanto occipital fusion reduces the foramen
magnum dimension leading to neurological
complications due to compression of spinal cord.
References:
- Albrecht, H.J.; Castrischer, E. (1968): Spaltbuilding in vorden
and hinteren altasbogen, Fortchr a.d. Geb. rontgenstr, 108:
543-545.
- Bailey, R.W.; Sherk H.H.; Don, E.J.; Fielding, J.W.; Martin
Long, D.; Uno K, Fening., L; Staufer, E.S: The cervical spine: occipitalization of Atlas. J.B. Lippincott company. Ptd in
U.S.A. p. 150 (1983).
- Budin, E; Sondheimer, F. (1966): Lateral spread of the atlas
without fracture. Radiology, 87: 1095-1098.
- Childers, J.C; Wilson, F.C; (1971): Bipartite Atlas. The
Journal of Bone and Joint surgery. 53A(3): 578-582.
- Englander, U. (1934): Uber spalt forminge Defekte bzw,
Persistierende knorpelfugen in Vorderen Atlasbogen.
Fortschr A.D. Gen Rontgnstr. 49U: 403-406.
- Greenbery, A.D. (1968): Atlanto - axial Dislocation, Brain 91:
655.
- Hadley, L.A. (1948): Atlanto - occipital fusion, ossiculum
terminale and occipital vertebra as related to basilar
impression with neurological symptoms. American Journal of
Roentgenology. 59: 511-523.
- Keller, H.L. (1961): formvarianten and fehlbildengen des atlas
and seiner umgebung. fortschr a.D. Gen. Roentgenstr. 95:
361-370.
- Krauffe (1965): Occipital dysplasia in infancy. Radiology.
85(3): 501-506.
- Kussmaul, A; Tenner, A: On the nature and origin of
epileptiform convulsions caused by profuse bleeding and also
of those of true epilepsy. Translated by Edward brunner
Londen, The New Sydenham society:p 109 (1859).
- Lopez Zanon, A; Limousin, L.A; Mantz, J.R. (1964):
Contribution a la sistematica dc las mal formations del atlas a
la luz de una neuva malformation inestable. Rev. clin,
Espanola. 94: 208-215.
- Macalister, A. (1893): Notes on the development and
variations of the atlas. Journal of Anatomy and Physiology.
27: 519-554.
- Mc, Rae, D.L.; Barnon, A.S. (1953): Occipitalization of atlas.
American Journal of Roentgenology 70: 23 - 45.
- Shipro, R; Robinson F. (1976): Anomalies of the cranio
vertebral border. American Journal of radiology. 127: 281
287.
- Vakili, S.T; Aguilar, J.C; Muller, J. (1985): Sudden
unexpected death associated with atlanto-occipital fusion.
The American Journal of Forensic Medicine and Pathology.:
6(1): 39-43.
Fig-1
Photograph of skull 1 showing atlanto-occipital fusion
with spina bifida posterior of atlas.
Fig-2
Photograph of skull-2 showing atlanto-occipital fusion.
Posterior arch of atlas is probably broken.
Department of Anatomy, M.S. Ramaiah Medical College, Bangalore- INDIA.
Abstract
Skeletal abnormalities at the craniocervical junction may result in sudden unexpected death. We report two skulls showing occipitalization of the atlas. Of the two skulls, one skull showed defect in ossification called "Spina-Bifida-Posterior". The fortuitous discovery of this skull with defects in ossification especially of the atlas prompted us to review the literature particularly on this developmental anomaly. Posterior-Spina-Bifida involves 3% of all the spines examined. Anterior and posterior foramen magnum dimensions were remarkably narrowed.
Key words: Atlas, Foramen Magnum, Anterior Arch, Posterior Arch, Occipital Bone.
Introduction:
Craniovertebral abnormalities have been recorded for many years in morphological and clinicoradiological studies.
Occipitalization of the atlas, assimilation of atlas or atlanto-occipital fusion is one of the common skeletal abnormalities of the upper cervical spine.
Hypoplasia of the basiocciput can be found in manifestations of the occipital vertebra, in atlas assimilation and in atlantooccipital fusion. These patients with craniovertebral joint anomalies exhibit the first neurological signs and symptoms usually no sooner than the second decade (Kruyff ; 1965).
Anomalies in the region of the foramen magnum were of the interest mainly to anatomists. (McRae & Bernon, 1953). These began to be described in pathological literature only in the later half of the 19th century.
Review of Literature:
Atlantooccipital fusion or occipitalization of atlas or assimilation of atlas has been extensively dealt with in the literature by craniologists. There are previous reports of both ossification defects and atlanto occipital fusion. Our study is compared with previous workers. These earlier reports are summarized below.
Table-1 Symptomatology of Atlanto-Occipital fusion.
Sr. No. | Author | Year | Symptoms |
---|---|---|---|
1. | Kussmaul & Tenner | 1859 | Convulsions in all 3 reported cases |
2. | Englander | 1934 | Cervical pain |
3. | Hadlay | 1948 | Neurological Symptoms. |
4. | Keller | 1961 | Seizure disorder |
5. | Lopez Zanon et al | 1964 | Cervical Pain in all 3 reported cases with tonic clonic convulsions in two out of them |
6. | Budin & Sondheimer | 1966 | Cervical pain following hyperextension and Onset of cervical pain while putting sweater |
7. | Albert & Castrischer | 1968 | Cervical Pain. |
8. | Childers & Wilson | 1971 | Pain in the neck in some of 25 reported cases; others being either asymptomatic or having insufficient clinical data |
9. | Vakili et al | 1985 | Sudden death. |
Case Report:
In our study related to foramen magnum we noticed two skulls each showing occipitalization of atlas. These were labelled I and II.
Skull I: Showed atlanto occipital fusion with associated spina bifida posterior of the atlas. This skull showed complete fusion of only one of the transverse processes with the occipital bone. The anterior arch of this atlas was incompletely fused with occipital bone (fig. 1).
Skull II: In this skull the anterior arch of atlas was fused with the occipital bone. This skull also showed fiusion of only one of the transverse processes of atlas to the occipital bone. One half of the posterior arch was fused with the occipital bone and the other half of the posterior arch was probably broken (fig. 2).
Embryology:
In some lower vertebrates (e.g.: Reptiles ) the cranial half of the first cervical sclerotome remains as a separate bone 'the proatlas' between the occiput and C1 vertebra. In man it becomes assimilated into the occipital condyles and also forms the tip of the dens. The caudal half of first cervical sclerotome gives rise to the lateral masses and the anterior and posterior arches of C1 vertebra. The body of C1 vertebra disappears early giving rise to all but the tip of the dens. The body, posterior arch and transverse process of C2 vertebra is derived from second cervial sclerotome. If the normal segmentation fails to occur, atlantooccipital fusion results. (Shipro & Robinson, 1976). The single anterior ossification of the first cervical vertebra is well described in the classic study of Macalister; 1893. According to him, "Two ossification centres appear, one just posterior to each of the lateral mass and transverse process". The two ossification centres meet in the middle, posteriorly usually by late in the fourth year of life. At about six months of age ossification begins in the anterior part of atlas generally by two closely approximated ossification centres, which usually unite within a few months of their apearance. Ocasionally there may be single anterior ossification centre. Ossification proceeds posterolaterally along both anterior and fusion to the lateral masses takes place in the fifth year of life (Macalister, (1893).
A midline defect can result from the failure of fusion of the ossification centres either anteriorly or posteriorly.
Discussion:
Neurological symptoms associated with occipitalization of the atlas are attributed to the ligamentous laxity of the transverse ligament about the odontoid process caused by repeated flexion and extension of the neck leading to the compression of the spinal cord or actual indentation of the medulla oblongata.
With aging, the central nervous system may be less tolerant to repeated blows from the odontoid. As per McRae's & Barnon (1953) study in 25 patients, they noticed 2 fusions of C2 and C3 vertebrae. The patient will be probably asymptomatic if the odontoid process is located below the level of foramen magnum. This relationship is best assessed through the use of McRaes & Barnon (1953) line which is drawn across the foramen magnum. Normally the odontoid process should not project above this line.
According to Greenberg (1968) spinal cord compression always occurs when the sagittal spinal canal diameter behind the odontoid process is less than or equal to 14 mm. Cord compression is possible when the sagittal canal diameter is between 15 and 17 mm. And almost never occurs at a distance of 18 mm or more.
According to McRae & Barnon (1953), patients with occipitalization of the atlas may have the following physical features: low hairline, torticollis, restricted neck movements and / or abnormal short neck. In neurological examination of the atlanto occipital fusion patient may reveal the following clinical findings: headache, neck pain, numbness and pain in the limbs, weakness, abnormal head posture, posteriorly located dull aching headache. Cranial nerve findings associated with occipitalization of the atlas include tinnitus, visual disturbances and lower cranial nerve palsies leading to dysphagia and dysarthria. The neurological symptoms and signs of atlanto-occipital fusion can not be distinguished from those of the Arnold Chiari malformation as the pathophysiology of both is essentially the same.
Fusion between atlas and occiput occurs anteriorly between the arch and rim of the foramen with some segment of the posterior arch of C1 present in some instances. This fragment can frequently constrict the spinal canal causing intermittent symptoms depending on the position of the head. (Bailay et al, 1983).
Conclusion:
Atlanto occipital fusion reduces the foramen magnum dimension leading to neurological complications due to compression of spinal cord.
References:
- Albrecht, H.J.; Castrischer, E. (1968): Spaltbuilding in vorden and hinteren altasbogen, Fortchr a.d. Geb. rontgenstr, 108: 543-545.
- Bailey, R.W.; Sherk H.H.; Don, E.J.; Fielding, J.W.; Martin Long, D.; Uno K, Fening., L; Staufer, E.S: The cervical spine: occipitalization of Atlas. J.B. Lippincott company. Ptd in U.S.A. p. 150 (1983).
- Budin, E; Sondheimer, F. (1966): Lateral spread of the atlas without fracture. Radiology, 87: 1095-1098.
- Childers, J.C; Wilson, F.C; (1971): Bipartite Atlas. The Journal of Bone and Joint surgery. 53A(3): 578-582.
- Englander, U. (1934): Uber spalt forminge Defekte bzw, Persistierende knorpelfugen in Vorderen Atlasbogen. Fortschr A.D. Gen Rontgnstr. 49U: 403-406.
- Greenbery, A.D. (1968): Atlanto - axial Dislocation, Brain 91: 655.
- Hadley, L.A. (1948): Atlanto - occipital fusion, ossiculum terminale and occipital vertebra as related to basilar impression with neurological symptoms. American Journal of Roentgenology. 59: 511-523.
- Keller, H.L. (1961): formvarianten and fehlbildengen des atlas and seiner umgebung. fortschr a.D. Gen. Roentgenstr. 95: 361-370.
- Krauffe (1965): Occipital dysplasia in infancy. Radiology. 85(3): 501-506.
- Kussmaul, A; Tenner, A: On the nature and origin of epileptiform convulsions caused by profuse bleeding and also of those of true epilepsy. Translated by Edward brunner Londen, The New Sydenham society:p 109 (1859).
- Lopez Zanon, A; Limousin, L.A; Mantz, J.R. (1964): Contribution a la sistematica dc las mal formations del atlas a la luz de una neuva malformation inestable. Rev. clin, Espanola. 94: 208-215.
- Macalister, A. (1893): Notes on the development and variations of the atlas. Journal of Anatomy and Physiology. 27: 519-554.
- Mc, Rae, D.L.; Barnon, A.S. (1953): Occipitalization of atlas. American Journal of Roentgenology 70: 23 - 45.
- Shipro, R; Robinson F. (1976): Anomalies of the cranio vertebral border. American Journal of radiology. 127: 281 287.
- Vakili, S.T; Aguilar, J.C; Muller, J. (1985): Sudden unexpected death associated with atlanto-occipital fusion. The American Journal of Forensic Medicine and Pathology.: 6(1): 39-43.

Fig-1
Photograph of skull 1 showing atlanto-occipital fusion with spina bifida posterior of atlas.

Fig-2
Photograph of skull-2 showing atlanto-occipital fusion. Posterior arch of atlas is probably broken.