Atlanto-occipital assimilation

Changed by Henry Knipe, 25 Oct 2022

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Atlanto-occipital assimilation is the fusion of the atlas (C1) to the occiput and is one of the transitional vertebrae.

Epidemiology

Atlanto-occipital assimilation occurs in approximately 0.5% (range 0.08-3%) of the population ^2-5,. It is thought to affect males and females equally.

Clinical presentation

It is typically asymptomatic but symptoms from nerve or vascular compression can occur.

Gross anatomy

Fusion of C1 to the occiput can be either ³:

complete: C1 not identifiable
incomplete: C1 partially identifiable

It can also be classified as

posterior arch assimilation
anterior arch assimilation or
assimilation of both the anterior and posterior arches

Associations

Atlanto-occipital assimilation is associated with ²:

fusion of C2 and C3 (occurs in 50% of cases)
basilar invagination: type 1
cleft palate
cervical ribs
urinary tract anomalies
cranio-cervical instability ⁵

-<p><strong>Atlanto-occipital assimilation</strong> is the fusion of the <a href="/articles/atlas-c1">atlas</a> (C1) to the occiput and is one of the <a href="/articles/transitional-vertebra">transitional vertebrae</a>. </p><h4>Epidemiology</h4><p>Atlanto-occipital assimilation occurs in approximately 0.5% (range 0.08-3%) of the population <sup>2-5,</sup>. It is thought to affect males and females equally.</p><h4>Clinical presentation</h4><p>It is typically asymptomatic but symptoms from nerve or vascular compression can occur. </p><h4>Gross anatomy</h4><p>Fusion of C1 to the occiput can be either <sup>3</sup>:</p><ul>
~~-<li>~~
~~-<strong>complete:</strong> C1 not identifiable</li>~~
~~-<li>~~
~~-<strong>incomplete:</strong> C1 partially identifiable</li>~~
~~-</ul><p>It can also be classified as </p><ul>~~
~~-<li>posterior arch assimilation</li>~~
~~-<li>anterior arch assimilation or</li>~~
~~-<li>assimilation of both the anterior and posterior arches</li>~~
~~-</ul><h5>Associations</h5><p>Atlanto-occipital assimilation is associated with <sup>2</sup>:</p><ul>~~
~~-<li>fusion of <a href="/articles/axis-c2">C2</a> and C3 (occurs in 50% of cases)</li>~~
~~-<li>~~
~~-<a href="/articles/basilar-invagination">basilar invagination</a>: type 1</li>~~
~~-<li><a href="/articles/cleft-palate">cleft palate</a></li>~~
~~-<li><a href="/articles/cervical-rib">cervical ribs</a></li>~~
~~-<li><a href="/articles/urinary-tract-anomalies">urinary tract anomalies</a></li>~~
~~-<li>~~
~~-<a href="/articles/cranio-cervical-instability">cranio-cervical instability</a> <sup>5</sup>~~
~~-</li>~~
+<p><strong>Atlanto-occipital assimilation</strong> is the fusion of the <a href="/articles/atlas-c1">atlas</a> (C1) to the occiput and is one of the <a href="/articles/transitional-vertebra">transitional vertebrae</a>. </p><h4>Epidemiology</h4><p>Atlanto-occipital assimilation occurs in approximately 0.5% (range 0.08-3%) of the population <sup>2-5,</sup>. It is thought to affect males and females equally.</p><h4>Clinical presentation</h4><p>It is typically asymptomatic but symptoms from nerve or vascular compression can occur. </p><h4>Gross anatomy</h4><p>Fusion of C1 to the occiput can be either <sup>3</sup>:</p><ul>
+<li>
+<strong>complete:</strong> C1 not identifiable</li>
+<li>
+<strong>incomplete:</strong> C1 partially identifiable</li>
+</ul><p>It can also be classified as </p><ul>
+<li>posterior arch assimilation</li>
+<li>anterior arch assimilation or</li>
+<li>assimilation of both the anterior and posterior arches</li>
+</ul><h5>Associations</h5><p>Atlanto-occipital assimilation is associated with <sup>2</sup>:</p><ul>
+<li>fusion of <a href="/articles/axis-c2">C2</a> and C3 (occurs in 50% of cases)</li>
+<li>
+<a href="/articles/basilar-invagination">basilar invagination</a>: type 1</li>
+<li><a href="/articles/cleft-palate">cleft palate</a></li>
+<li><a href="/articles/cervical-rib">cervical ribs</a></li>
+<li><a href="/articles/urinary-tract-anomalies">urinary tract anomalies</a></li>
+<li>
+<a href="/articles/cranio-cervical-instability">cranio-cervical instability</a> <sup>5</sup>
+</li>

References changed:

1. Smoker W. Craniovertebral Junction: Normal Anatomy, Craniometry, and Congenital Anomalies. Radiographics. 1994;14(2):255-77. <a href="https://doi.org/10.1148/radiographics.14.2.8190952">doi:10.1148/radiographics.14.2.8190952</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/8190952">Pubmed</a>
2. Arthur C. Aufderheide, Conrado Rodriguez-Martin. The Cambridge Encyclopedia of Human Paleopathology. (1998) ISBN: 9780521552035 - <a href="http://books.google.com/books?vid=ISBN9780521552035">Google Books</a>
3. Jrgen Freyschmidt, Joachim Brossmann. Koehler/Zimmer's Borderlands of Normal and Early Pathological Findings in Skeletal Radiography. (2011) ISBN: 9783131606358 - <a href="http://books.google.com/books?vid=ISBN9783131606358">Google Books</a>
4. Electricwala A, Harsule A, Chavan V, Electricwala J. Complete Atlantooccipital Assimilation with Basilar Invagination and Atlantoaxial Subluxation Treated Non-Surgically: A Case Report. Cureus. 2017;9(6):e1327. <a href="https://doi.org/10.7759/cureus.1327">doi:10.7759/cureus.1327</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/28690960">Pubmed</a>
5. Ferreira E & Botelho R. Atlas Assimilation Patterns in Different Types of Adult Craniocervical Junction Malformations. Spine (Phila Pa 1976). 2015;40(22):1763-8. <a href="https://doi.org/10.1097/BRS.0000000000001045">doi:10.1097/BRS.0000000000001045</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/26165213">Pubmed</a>
1. Smoker WR. Craniovertebral junction: normal anatomy, craniometry, and congenital anomalies. Radiographics. 1994;14 (2): 255-77. <a href="http://dx.doi.org/10.1148/radiographics.14.2.8190952">doi:10.1148/radiographics.14.2.8190952</a> - <a href="http://www.ncbi.nlm.nih.gov/pubmed/8190952">Pubmed citation</a><span class="auto"></span>
2. Aufderheide AC, Rodriguez-Martin C. The Cambridge encyclopedia of human paleopathology. Cambridge University Press. ISBN:0521552036. <a href="http://books.google.com/books?vid=ISBN0521552036">Read it at Google Books</a> - <a href="http://www.amazon.com/gp/product/0521552036">Find it at Amazon</a><span class="auto"></span>
3. Koehler/Zimmer's Borderlands of Normal and Early Pathological Findings in Skeletal Radiography. Thieme. (2003) ISBN:3131606355. <a href="http://books.google.com/books?vid=ISBN3131606355">Read it at Google Books</a> - <a href="http://www.amazon.com/gp/product/3131606355">Find it at Amazon</a><span class="ref_v3"></span>
4. Electricwala AJ, Harsule A, Chavan V, Electricwala JT. Complete Atlantooccipital Assimilation with Basilar Invagination and Atlantoaxial Subluxation Treated Non-Surgically: A Case Report. (2017) Cureus. 9 (6): e1327. <a href="https://doi.org/10.7759/cureus.1327">doi:10.7759/cureus.1327</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/28690960">Pubmed</a> <span class="ref_v4"></span>
5. Ferreira ED, Botelho RV. Atlas Assimilation Patterns in Different Types of Adult Craniocervical Junction Malformations. (2015) Spine. 40 (22): 1763-8. <a href="https://doi.org/10.1097/BRS.0000000000001045">doi:10.1097/BRS.0000000000001045</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/26165213">Pubmed</a> <span class="ref_v4"></span>

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