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Skeletal Radiology

, Volume 48, Issue 2, pp 323–324 | Cite as

Post-auricular lump: CT diagnosis

  • Ying Liang LowEmail author
  • Soon Yiew Sia
  • Salil Babla Singbal
  • Sterling Ellis Eide
  • Junwei Zhang
Test Yourself: Answer
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Answer: Paracondylar process-epitransverse process complex

On the computed tomography (CT) scan, there was a well-defined bony protuberance just lateral to the left occipital condyle, in keeping with a paracondylar process. It extended inferiorly to articulate with a separate 1.4-cm osseous fragment, which in turn articulated with a protuberance from the left transverse process of the atlas (epitransverse process; Fig. 1 for diagrammatic representation). The findings corresponded to the clinically palpable lump with no other osseous or soft-tissue mass lesion identified.
Fig. 1

Illustrated diagram of the craniovertebral junction in a the posterior projection and b the left anterior oblique projection. ETP epitransverse process, LM lateral mass, OC occipital condyle, PP paracondylar process, TP transverse process

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 [3]. It may be present as a small hump (paracondylar tuberculum), a free-ended process or may articulate with the C1 transverse process [3]. If the process detaches and assimilates to the C1 transverse process instead, an epitransverse process is formed [3]. Our patient has an unusual variation where both paracondylar and epitransverse processes coexist [4]. 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 [9]. It may also present as an osseous lump (as in our patient) [2] or more frequently as an incidental imaging finding [10]. 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 [3], 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 [7].

When symptomatic, conservative treatment usually suffices, although there are reports of symptomatic relief with surgical resection [7, 8].

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.

Notes

Compliance with ethical standards

Conflicts of interest

The authors declare that they have no conflicts of interest.

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Copyright information

© ISS 2018

Authors and Affiliations

  1. 1.Department of Diagnostic Imaging, National University HospitalNational University Health SystemSingaporeSingapore

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