Increased Retro-Odontoid Soft Tissue Ratio: A Risk Factor for Symptomatic Retro-Odontoid Pseudotumor Following Laminoplasty

Objective: This study examines the risk of developing symptomatic retro-odontoid pseudotumor (ROP) following cervical laminoplasty. ROP can result in cervical myelopathy, leading to substantial morbidity. Identifying the risk factors for symptomatic ROP is essential to improving patient outcomes after laminoplasty. Methods: The study included 2 symptomatic ROP patients and 2 additional cases from the literature, compared with a cohort of 57 non-ROP patients who underwent Hirabayashi open-door laminoplasty. Radiological assessments were conducted to evaluate cervical spine alignment, including MRI and postoperative dynamic radiographs. A novel index, the retro-odontoid soft tissue ratio (RS ratio), was introduced to quantify the extent of retro-odontoid soft tissue compression. Results: The study included 4 ROP patients (mean age: 68.5 years; all males) and 57 non-ROP patients (mean age: 65.7 years; 32 males, 25 females). The mean follow-up duration was 93.0 months (range: 48–156) for the ROP group and 32.5 months (range: 3–101) for the non-ROP group. The ROP group had significantly higher preoperative RS ratios (46.11 ± 4.80%) compared to the non-ROP group (30.29 ± 4.94%, P < 0.05). Postoperative cervical mobility assessment showed no significant difference in occipital-C2 (O-C2) contribution between the groups, with the ROP group at 59.82 ± 17.14% and the non-ROP group at 47.79 ± 14.17% (P = 0.13). The mean O-C7 range of motion (ROM) was lower in the ROP group (38.42 ± 16.23°) compared to the non-ROP group (49.69 ± 14.89°), but the difference was not statistically significant (P = 0.23). However, the change in O-C2 ROM was significantly different between the groups, with the ROP group showing an increase of +7.23 ± 4.70°, while the non-ROP group showed a decrease of −0.04 ± 9.90° (P < 0.05). Conclusions: This study highlights that a high preoperative RS ratio is a significant risk factor for symptomatic ROP, with a notable increase in O-C2 ROM observed in the ROP group following laminoplasty. These findings suggest that ROP is a progressive condition that may worsen after surgical intervention, particularly in patients with pre-existing retro-odontoid masses.