Citation, DOI, disclosures and article data
At the time the article was created Matt Skalski had no recorded disclosures.View Matt Skalski's current disclosures
The paracondylar process, also known as the paraoccipital, paramastoid, parajugular or estiloid process, is a rare anatomical variant of the occipital where a bony exostosis extends caudally from the paracondylar region (lateral to the native occipital condyles), typically articulating with the superior surface of a transverse process of the atlas. It is part of the spectrum of occipital vertebrae 1.
Paracondylar processes are rare, with a reported prevalence of 0.5-2% 2. They may be unilateral or bilateral, with unilateral reported to be the most common 3.
A paracondylar process is usually an incidental finding, though it may be symptomatic if it fuses or articulates with the transverse process of the atlas (C1) below it, resulting in reduced atlanto-occipital range of motion or bony torticollis that may necessitate surgery 1,2.
The paracondylar process is best depicted on coronal CT, where it appears as a broad-based bony protruberance arising from the inferior aspect of the jugular process of the occipital bone, immediately lateral to the occipital condyle 1,4,5. Its shape has been likened to that of an inverted cone or a molar tooth and it may be solid or pneumatized, with considerable variation between individuals 1,4.
The paracondylar process is directed inferiorly, passing lateral to the occipital artery, medial to the mastoid process and posterior to the jugular fossa. It may fuse or articulate with the superior surface of the transverse process of the atlas located below it 1.
The various combinations of bony attachments of the paracondylar process have given rise to a multitude of names 6:
paracondylar tubercle: shallow hump fused to the occipital bone only
paracondylar process: process fused to the occipital bone only
may articulate with the transverse process of the atlas
massa paracondylica: unfused accessory ossicle
may articulate with the occipital bone and/or the transverse process of the atlas
epitransverse process: process fused to the transverse process of the atlas only
may articulate with the occipital bone
isolated epitransverse process: process fused to the transverse process of the atlas only
does not articulate with the occipital bone
The paracondylar process develops due to a phenomenon known as caudal shifting, whereby the component sclerotomes of the embryonic proatlas (i.e. the caudal part of the fourth occipital sclerotome and the first cervical sclerotome) fail to separate normally. The broad array of paracondylar process sub-variants is said to be a result of variable degrees of separation between the sclerotomes 1.
In recent literature, the prevailing mechanism is the one described above. Some authors would advocate for an alternate acquired or post-traumatic mechanism secondary to tension on the rectus capitis lateralis muscle or lateral atlanto-occipital ligament, as both attach near the jugular process from which the paracondylar process arises 1,2.
See the article on occipital vertebrae for a detailed discussion of the embryonic origin of this spectrum of variants.
The paracondylar process may be a hindrance during far lateral approach neck dissection or surgery of the dural venous sinuses 1,6.
calcified stylohyoid ligament: slimmer shape and directed more medially than a paracondylar process 7
- 1. Schumacher M, Yilmaz E, Iwanaga J, Oskouian R, Tubbs R. Paramastoid Process: Literature Review of Its Anatomy and Clinical Implications. World Neurosurg. 2018;117:261-3. doi:10.1016/j.wneu.2018.06.056 - Pubmed
- 2. Nolet PS, Friedman L, Brubaker D. Paracondylar process: a rare cause of craniovertebral fusion—a case report. Journal of the Canadian Chiropractic Association. 1999;43(4):229-235. Pubmed
- 3. Pace JL. The paramastoid process : a survey of 890 Maltese skulls. The St. Luke's Hospital Gazette. 1969;4(1):34-42. -
- 4. Prescher A, Brors D, Adam G. Anatomic and Radiologic Appearance of Several Variants of the Craniocervical Junction. Skull Base. 1996;6(02):83-94. doi:10.1055/s-2008-1058649 - Pubmed
- 5. Narayanan R, Shankar B, Paruthikunnan S, Kulkarni C. Paracondylar Process of the Occipital Bone of the Skull: A Rare Congenital Anatomical Variant. Case Reports. 2014;2014(oct15 1):bcr2014205315. doi:10.1136/bcr-2014-205315 - Pubmed
- 6. Prescher A, Schuster D, Brors D. GMS. Some Rare Osseous Variations of the Craniocervical Junction. 7th Congress of the European Skull Base Society Held in Association with the 13th Congress of the German Society of Skull Base Surgery. 2009. doi:10.3205/05esbs02
- 7. Terry R. Yochum, Lindsay J. Rowe. Essentials of Skeletal Radiology. (1996) ISBN: 0683093304 - Google Books