CT scans reveal how the styloid process varies in a Nepalese population

The styloid process, a thin bony projection arising just in front of the stylomastoid foramen, anchors the stylohyoid and stylomandibular ligaments and the stylohyoid, styloglossus and stylopharyngeus muscles, structures involved indirectly in speech, swallowing and head movement. When this process grows unusually long or develops an abnormal shape, it can press on nearby nerves and vessels and produce the throat pain, difficulty swallowing and facial pain characteristic of Eagle’s syndrome. Yet population-specific data on its dimensions remain scarce in many parts of the world, which is precisely the gap a team at Manipal Teaching Hospital in Pokhara set out to fill.

The study, published in Discover Imaging, was a descriptive cross-sectional analysis of 124 head CT scans obtained from patients who came for imaging of the head and neck region at Manipal Teaching Hospital, part of Manipal College of Medical Sciences, between 21 July 2021 and 2 July 2022. Ethical approval came from the institution’s review committee and the Nepal Health Research Council, and all participants gave written informed consent. The researchers used non-probability convenience sampling and calculated a target sample size of 134 with G*Power software, based on a reported prevalence, an effect size of 0.3, an alpha of 0.05 and 95 percent power; the final study sample comprised 124 scans. Imaging was performed on a 128-slice multidetector CT scanner, which acquires thin-section isotropic images suited to the multiplanar reconstruction needed to trace and measure the styloid processes on both sides of the skull.

The investigators deliberately excluded scans that could confound the anatomy. Images showing an incomplete or unilateral styloid process, errors in size or shape, or questionable morphology were left out, as were cases with pathologies known to hinder normal development, such as congenital anomalies, trauma or metabolic bone disorders, and conditions that might alter styloid morphology, including Eagle’s syndrome itself and abnormal ossification. That means the figures describe a hospital-based sample selected to reflect typical anatomy rather than disease. Measurements covered the length of each styloid process, its morphological type and the distance between the oropharynx and the tip of the process, taken bilaterally with the scanner’s own software and Osirix MD, on 3 mm sections. Following the literature, a normal styloid process was considered to measure 20 to 30 mm, and processes were classified as Type I when elongated and uninterrupted, Type II when pseudoarticulated, attached to adjacent ligaments by a false joint, or Type III when segmented, with discontinuous mineralized segments.

The 124 scans came from 64 males and 60 females aged 10 to 90 years, with a mean age of 47.66 years and a standard deviation of 20.16 years. Participants were grouped as adolescents under 18, adults from 18 to 65 and elderly people over 65, following World Health Organization age classifications; most participants were adults, numbering 89, while adolescents were the smallest group at 9. Across the whole sample, the average styloid process length was 27.12 plus or minus 8.58 mm on the right side and 26.37 plus or minus 7.21 mm on the left, a small difference that reached statistical significance at p of 0.0001 or below. The right and left measurements correlated strongly and positively, with a correlation coefficient of 0.69, suggesting that the two sides generally grow in proportion to one another.

Sex differences emerged in the raw numbers but not in the statistics. Males averaged 27.47 plus or minus 8.23 mm overall against 25.97 plus or minus 7.54 mm in females, a gap that was not statistically significant at p equal to 0.13. Broken down by side, males measured 27.98 plus or minus 9.46 mm on the right and 26.97 plus or minus 6.81 mm on the left, while females measured 26.20 plus or minus 7.51 mm on the right and 25.75 plus or minus 7.63 mm on the left, so the right side was longer in both sexes. Neither the sex comparison on the right at p equal to 0.25 or the left at p equal to 0.34, nor the paired side-to-side comparisons at p equal to 0.30 and 0.38, reached significance. Age told a similar story of apparent but statistically unconfirmed variation: the longest mean right-sided length appeared in the elderly at 27.51 plus or minus 11.00 mm, while the left side was longest in adolescents at 27.33 plus or minus 7.37 mm, with no significant differences across age groups on either side. The single longest process measured 67.70 mm on the right side of a 69-year-old man, and the shortest was 10.20 mm in a 27-year-old woman.

The most striking figure concerned elongation. Of the 124 scans, 41, or 33.06 percent, showed at least one styloid process of 30 mm or longer. Elongation was unilateral in 15.32 percent of cases, 19 radiographs, and slightly more common in males, at 18.75 percent, than in females. Bilateral elongation appeared in 22 radiographs, or 17.74 percent, with a marginally higher incidence in females, at 20 percent. Most participants of both sexes had bilateral processes under 30 mm, 65.62 percent of males and 68.33 percent of females. The authors note that abnormally long processes or mineralization of the stylohyoid ligament complex can underlie Eagle’s syndrome, in which patients may experience dysphagia, odynophagia, a persistent foreign-body sensation in the throat and facial or cervical pain radiating to the ear, and in rare cases vascular complications such as carotid artery dissection or transient ischemic attacks.

Distance from the oropharynx, a parameter the authors say is rarely reported, averaged 23.45 plus or minus 5.93 mm on the right and 23.25 plus or minus 6.15 mm on the left across the sample. Males showed slightly larger distances than females on both sides, but the differences were not statistically significant. Across age groups the averages ranged from about 20.7 mm in adolescents to about 23.9 mm in adults on the right side, again without significant differences. The closest approach of a styloid tip to the oropharynx, 2.50 mm, was recorded on the right side of a 29-year-old man, while the greatest distance, 47.60 mm, was seen on the right side of a 20-year-old woman. Strong bilateral correlations in this distance appeared in adolescents and adults, with correlation coefficients of 0.92 and 0.80 respectively.

Morphological typing added a developmental dimension. Type I, the elongated uninterrupted form, was the most common pattern overall and predominated in adults, at 44.9 percent on the right and 47.2 percent on the left, and in the elderly, at 57.7 percent on the right and 50 percent on the left. Adolescents instead showed a high prevalence of Type III, the segmented form, at 77.8 percent on both sides, while Type II was entirely absent in that youngest group. By sex, Type I led in both males and females, but Type III was more frequent in females, at 40 percent on the right and 45 percent on the left, than in males. None of these distributions differed significantly by age or sex in chi-square testing. The authors suggest the pattern may reflect developmental or sex-related influences, noting that Types II and III have been more often associated with Eagle’s syndrome and related neurovascular complications in the literature.

Placed against earlier work, the Nepalese means sat below those reported in Turkish CT studies and above those from Indian panoramic radiographic and dry skull studies, with the authors attributing cross-population differences to methodology and to variation in skeletal growth and hormonal influences on bone development. They also caution that the study has real limits: the sample is small, drawn by convenience from a single tertiary centre in western Nepal, and therefore may not generalize across the country’s regional and ethnic diversity. Even so, the team argues that baseline data of this kind matter clinically, helping radiologists interpret scans, avoid misdiagnosing pharyngeal or cervical pathology, and plan procedures such as styloidectomy, while diagnosis of Eagle’s syndrome, they stress, should never rest on styloid length alone.

Subject of Research: Computed tomographic assessment of styloid process length, type and position in western Nepal

Article Title: Computed tomographic evaluation of the morphology of styloid process of temporal bone among people attending a tertiary care center in Nepal

Article References: Bhattarai, C., Poudel, P. P., Gautam, S., Basnet, L. M., Basnet, S. B., Sharma, P., & Koirala, K. P. (2025). Computed tomographic evaluation of the morphology of styloid process of temporal bone among people attending a tertiary care center in Nepal. Discover Imaging, 2(1), Article 14. https://doi.org/10.1007/s44352-025-00018-x

Image Credits: AI Generated

DOI: 10.1007/s44352-025-00018-x

Keywords: styloid process, temporal bone, computed tomography, Eagle syndrome, anatomy, Nepal, elongated styloid process, morphology, radiology, otolaryngology, Computed, tomographic