Abstract

Background: Retro-odontoid pseudotumors (ROPs) typically present as a single mass posterior to the odontoid ranging from isointense to hypointense relative on T1-weighted magnetic resonance (MR) imaging (MRI T1WI). Here, a patient with ROP exhibited the double-layer sign on the MRI T1WI characterized by an initial ventral layer posterior to the odontoid process followed by a secondary dorsal layer.

Case Description: An 84-year-old male presented with cervical myelopathy attributed to ROP resulting in atlantoaxial instability on dynamic X-ray studies, and the double-layer sign on the T1 MR accompanied by a cystic component. MR following C1–C2 posterior fusion, the patient’s myelopathy resolved and both layers spontaneously regressed on the follow-up MR studies.

Conclusion: The MR-documented double layer sign with ROP, likely attributable to reactive hypertrophy of the transverse ligament with cystic components, may demonstrate spontaneous MR regression with symptom resolution following a C1–C2 posterior fusion.

Keywords: Double layer, Pseudotumor, Retro-odontoid tumor

INTRODUCTION

Double-layer retro-odontoid pseudotumors (ROPs) are nonneoplastic inflammatory lesions (i.e., most likely due to mechanical stress and composed of fibrous granulation/fibrocartilaginous tissues) that may extend from the clivus to the C2–C4 levels and contribute to spinal compression.[ 1 - 3 ] Both layers are hypointense to isointense on T1-weighted magnetic resonance (MR) imaging (MRI T1WI) and hypointense to mixed intensity on T2-weighted MR studies. Here, we describe an 84-year-old male whose preoperative double-layer ROP findings of spinal cord compression regressed on follow-up MR studies after a C1–C2 posterior fusion.

CASE DESCRIPTION

An 84-year-old male presented with cervical myelopathy due to ROP. Flexion-extension roentgenograms showed atlantoaxial subluxation. T1 and T2 MR studies demonstrated ROP and the double-layer sign; T1 unenhanced MR studies showed that both layers were isointense areas while T2 MR showed a mixed intensity secondary dorsal layer [ Figures 1a and b ]. The patient’s cervical myelopathic deficits resolved following a C1–C2 posterior decompression and fusion. On follow-up MR studies, both layers regressed [ Figure 2 ].

Figure 1:

Preoperative magnetic resonance imaging (MRI) T1WI and T2WI sagittal view. T1-weighted magnetic resonance (MR) imaging demonstrated retro-odontoid pseudotumor with double-layer sign; T1 MR showed both layers with isointense areas (a) while T2 MR showed mixed intensity areas of a secondary dorsal layer (b).

Figure 2:

Postoperative MRI T1WI. The patient was treated by posterior fusion and both layers were regressed.

DISCUSSION

Etiology of ROP double-layer sign

Some causes of ROP involve cyst formation, which can potentially grow to exceptionally large sizes extending from clivus to the caudad C2–C4 levels [ Table 1 ].[ 1 - 3 ] ROP cysts are likely attributed to atlantoaxial degenerative articular cyst formation and may reflect;[ 1 ] micro-bleeding,[ 5 ] loculated collections of mucinous fluid from synovium,[ 4 ] and relatively higher amounts of hyaline cartilage.[ 6 ] Here, the composition of the ventral layer of ROP was attributed to a thickened transverse ligament with fibrocartilage metaplasia, while the dorsal layer was due to a cystic component (i.e., the septum of the posterior longitudinal ligament/tectorial membrane).

Table 1:

A summary of causative factors forming retro-odontoid pseudotumor.

CONCLUSION

The MR-documented double-layer sign with ROP was likely attributable to reactive hypertrophy of the transverse ligament with cystic components. Spontaneous regression of the double-layer sign after posterior C1–C2 fusion correlated with the patient’s resolved myelopathy.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

1. Birch BD, Khandji AG, McCormick PC. Atlantoaxial degenerative articular cysts. J Neurosurg. 1996. 85: 810-6

2. Goel A, Darji H, Shah A, Prasad A, Hawaldar A. Retroodontoid and retro-C2 body pseudotumor, pannus, and/or cyst. A study based on analysis of 63 cases. World Neurosurg. 2021. 151: e170-7

3. Sagiuchi T, Shimizu S, Tanaka R, Tachibana S, Fujii K. Regression of an atlantoaxial degenerative articular cyst associated with subluxation during conservative treatment. Case report and review of the literature. J Neurosurg Spine. 2006. 5: 161-4

4. Sheen JJ, Seo DK, Rhim SC, Choi SH. Hemorrhagic synovial cyst associated with rheumatoid atlantoaxial subluxation. Korean J Spine. 2013. 10: 85-7

5. Takeuchi M, Yasuda M, Takahashi E, Funai M, Joko M, Takayasu M. A large retro-odontoid cystic mass caused by transverse ligament degeneration with atlantoaxial subluxation leading to granuloma formation and chronic recurrent microbleeding case report. Spine J. 2011. 11: 1152-6

6. Yu E, Montanera W. Periodontoid pseudotumor: CT and MRI imaging. Neuroradiology. 2005. 47: 328-33