Post-auricular lump: CT diagnosis
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Answer: Paracondylar process-epitransverse process complex
The craniovertebral junction is an anatomically complex region with a variety of developmental anomalies that may arise from incomplete assimilation of the proatlas somite into the occiput [1, 2, 3]. The paracondylar process (PCP) is one such rare entity. It arises adjacent to the occipital condyle and is directed toward the ipsilateral C1 transverse process . It may be present as a small hump (paracondylar tuberculum), a free-ended process or may articulate with the C1 transverse process . If the process detaches and assimilates to the C1 transverse process instead, an epitransverse process is formed . Our patient has an unusual variation where both paracondylar and epitransverse processes coexist . In addition, to our knowledge, a multi-segmented appearance of two separate pseudo-articulations with the occipital bone and C1 transverse process has not been previously reported.
The reported prevalence of the PCP varies from 0.077 to 4% depending on the population studied and it can be unilateral or bilateral [1, 3, 5, 6, 7]. The PCP is usually asymptomatic, but may rarely present with headache, neck ache, and even restricted head movement, including osseous torticollis [3, 6, 7, 8], especially if large or articulating with the C1 transverse process . It may also present as an osseous lump (as in our patient)  or more frequently as an incidental imaging finding . Compression of the adjacent vertebral artery and C1 nerve root may hypothetically lead to symptoms, but this has not been documented in previous case reports [2, 4].
The PCP is difficult to identify on radiographs owing to superimposed structures , but is well-delineated on multiplanar CT, which also allows differentiation from other entities such as the calcified stylohyoid ligament, which is thinner and directed medially [6, 9, 10]. It also facilitates detection of other cervical spine anomalies, which often co-exist .
The radiologist may often be the first to detect the presence of a PCP, which is frequently incidental or clinically unsuspected. Awareness of this rare variant will allow confident radiological diagnosis and prompt reassurance regarding its benign nature.
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Conflicts of interest
The authors declare that they have no conflicts of interest.
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