## 4 Discussion  
This study sheds light on the prevalence and clinical significance of Atlas Posterior Arch Deficiency (APAD) among a cohort of 500 Italian patients. The detection of APAD through CBCT imaging has proven to be a valuable diagnostic tool, revealing that this anatomical variation, though relatively rare, holds notable clinical importance. Congenital anomalies of the posterior atlas arch, such as atlanto-occipital assimilation and posterior arch aplasia (APAD), often present diagnostic challenges due to their typically asymptomatic nature and incidental discovery during radiographic examination. Effective identification and assessment of these anomalies are crucial for accurate diagnosis and appropriate management [10; 11; 12]. Cone-beam computed tomography (CBCT) has proven invaluable in the precise visualization and classification of APAD. CBCT provides high-resolution, three-dimensional imaging of the cervical spine, enabling the detailed examination of anatomical structures and abnormalities. This advanced imaging modality offers superior spatial resolution compared to conventional radiography, facilitating the detection of subtle variations in the atlas arch morphology associated with APAD. In this study, the 13 identified cases of Type A APAD are described in Table 3 and reflect findings consistent with prior research. For instance, [PERSON] et al. (2011) [7] described the congenital cleft of the anterior arch and the partial aplasia of the posterior arch, highlighting the diagnostic importance of such anomalies. Similarly, [PERSON] et al. (2003) reported a case where the partial aplasia of the posterior arch led to myelopathy, emphasizing the potential neurological consequences [8]. \begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Case**} & \multirow{2}{*}{**Age**} & \multirow{2}{*}{**Type of APAD**} & \multirow{2}{*}{**Presence of** **Ponticulus**} & \multirow{2}{*}{**Symptoms**} & \multirow{2}{*}{**Management**} & \multirow{2}{*}{**Outcome**} \\  & & & & & & \\ \hline \multirow{3}{*}{1} & \multirow{3}{*}{17 years} & Complete & Bilateral & neck stiffness; no & Routine monitoring; & Remained \\  & & APAD & & & significant & no immediate & symptom-free; \\  & & APAD & Complete & neurological & intervention & routine imaging \\  & & & & symptoms & required & for follow-up \\ \hline \multirow{3}{*}{2} & \multirow{3}{*}{54 years} & Partial & \multirow{3}{*}{Unilateral} & Mild to moderate & Physical therapy and & Symptoms \\  & & & & neck pain; & NSAIDs; follow-up & improved; no \\  & & & & & intermittent tingling & imaging & significant defect \\  & & & & in right upper limb & recommended & progression \\ \hline \multirow{3}{*}{3} & \multirow{3}{*}{35 years} & Partial & \multirow{3}{*}{None} & \multirow{3}{*}{\
\begin{tabular}{c} Crosservative \\ treatment; \\ monitoring for any \\ symptoms reported \\ \end{tabular} } & \multirow{3}{*}{
\begin{tabular}{c} Stable condition; \\ no significant \\ \end{tabular} } \\  & & & & & \\ \hline \multirow{3}{*}{4} & \multirow{3}{*}{42 years} & Partial & \multirow{3}{*}{None} & Mild neck & Conservative \\  & & & discomfort; no & management; \\  & & & significant & regular follow-up & \\  & & & symptoms & and monitoring & follow-up \\ \hline \multirow{3}{*}{5} & \multirow{3}{*}{31 years} & Partial & \multirow{3}{*}{None} & Mild neck stiffness; & Routine monitoring; & No progression; \\  & & & no significant & conservative care as & symptoms \\  & & & symptoms & needed & remained stable \\ \hline \end{tabular}
\end{table} 
Table 3: Summary of symptoms, management, and outcomes of 13 cases of Atlantal Posterior Arch Defect (APAD). [PERSON] et al. (2018) [9] and [PERSON] et al. (2013) [10] have contributed valuable insights regarding the prevalence and clinical presentations of C1 arch anomalies, reinforcing the need for thorough evaluation in patients with cervical spine symptoms. The classification systems by [PERSON] et al. (2009) [13] and [PERSON] et al. (2021) [14] aid in categorizing these anomalies, improving communication among clinicians.