PMC9719744_01
Preoperative T2-weighted MRI at initial diagnosis (A-C) and 4 years before (D). A cystic mass (arrow) was observed adjacent to the posteromedial site of the right atlantoaxial joint and the retro-odontoid pseudotumor (asterisk) (A-C). A solid small mass with iso-signal intensity (arrowhead) was present inside the cyst (B, C). The retro-odontoid pseudotumor had grown in size comparing the finding at 4 years before (A, D).
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Magnetic resonance imaging (MRI) revealed a cystic mass occupying the right one-third part of the spinal canal and compressing the spinal cord (Fig. 1A-C). However, this was not observed on MRI 4 years prior (Fig. 1D). Retro-odontoid pseudotumor (ROP) grew in size during the 4 years (Fig. 1A and B).
Intraoperative views of the intradural synovial cyst (A, C) and a finding of intraoperative ultrasonography (B). Histopathological image of the cyst (hematoxylin and eosin stain, x100, scale bar 200 mum) (D).
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A: Location of the cystic mass was pointed out by the arrow, but the mass was not recognized from the view of the surface after partial laminectomy of the atlas.
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B: Intraoperative ultrasonography showed that the cyst (arrowhead) was located on the right side of the spinal cord (asterisk) in the dura mater.
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C: After opening the cyst, a yellow solid mass (arrowhead) was observed on the right lateral side of the spinal cord.
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D: After debulking the cystic mass, the cyst wall was dissected around the whole surface.
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E: Small penetration was identified at the anterior wall of the thecal sac after removal of the cystic mass.
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F: Histopathological examination revealed a multiloculated cyst-like structure, with hyperplasia of collagen fiber (arrow), infiltration of inflammatory cells such as lymphocytes and macrophage (arrowhead), and growth of capillaries.
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At first, we could not find the cystic mass from the surface view in the spinal canal (Fig. 2A). Using intraoperative ultrasonography, we noticed that the cyst was located in the thecal sac (Fig. 2B). After clear serous fluid drained out, a yellow solid mass was observed under the arachnoid membrane adjacent to the right lateral side of the spinal cord (Fig. 2C). After debulking the cystic mass, the cyst wall was dissected around the whole surface (Fig. 2D). After removal of the cystic mass, small penetration was observed at the anterior wall of the thecal sac (Fig. 2E). Histopathological examination revealed a multiloculated cyst-like structure, with hyperplasia of collagen fiber (Fig. 2F, arrow), infiltration of inflammatory cells such as lymphocytes and macrophages (Fig. 2F arrowhead), and growth of capillaries.
Postoperative T2-weighted MRI at 1 month (A, B) and at 3 years postoperation (C, D). A month postoperative sagittal (A) and axial (B) MRI showed the cyst and internal masses were resected, and the pseudotumor (asterisk) was reduced in size and spinal cord decompression was achieved. Three years postoperative sagittal (C) and axial (D) MRIs show no recurrence of the cyst and no growth of the pseudotumor (asterisk).
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Postoperative MRI showed adequate decompression of the spinal cord (Fig. 3A and B). Recurrence of the cyst was not observed until the latest follow-up after 3 years, during which the ROP decreased in size (Fig. 3C and D).