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. 2021 Mar 2;94(1119):20200798. doi: 10.1259/bjr.20200798

Table 2.

Assessment of normal MRN findings and anatomical benchmark nerve diameters (Attention: this does not necessarily correspond to MRN nerve diameters which reflect signal intensities)

Assessment of normal MRN findings

  1. Normal anatomical course

  2. Progressive and discrete decrease in caliber and signal intensity towards distal

  3. No noticeable sudden interruptions or compressions

  4. No perineural scarring

  5. No focal swellings and/or signal alterations (no bright-black-bright sign)

  6. No abnormalities at the level of the target organs

Anatomical benchmark nerve diameters
Nerve Site of measurement Mean diameter (mm) ±standard deviation Reference
Trigeminal nerve
 V1: Ophthalmic division Middle cranial fossa 1.7 ± 0.1 Pennisiet al45
 V2: Maxillary division Middle cranial fossa 4.01 ± 0.52 Zhang et al46
 V2: infraorbital nerve Infraorbital foramen 3.30 ± 0.52 Zhang et al46
 V3: Mandibular division Middle cranial fossa 7.41 ± 1.41 Soeira et al47
 V3: Inferior alveolar nerve Mandibular foramen 2.2 ± 0.4 Ikeda et al48
 V3: Mental nerve Mental foramen 1.68–2.37 Gershenson et al49
 V3: Lingual nerve Third molar region 3.0 ± 0.5 VonArx et al50
 V3: Auriculotemporal After fusion of rootlets 3.18 ± 0.84 Komarnitki et al51
Facial nerve
 Segment Labyrinth 1.13 ± 0.39 Vianna et al52
Tympanic 1.09 ± 0.57 Vianna et al52
Mastoid 1.33 ± 0.65 Vianna et al52
Average between stylomastoid foramen and intraparotid branching 1.4 ± 0.2 Lo et al53
 Peripheral branch Intraparotid 0.5 ± 0.1 Tawfik et al54
Temporal branch 0.94 ± 0.33 Martínez Pascual et al55
Zygomatic 1.00 ± 0.46 Martínez Pascual et al55
Buccal 0.99 ± 0.40 Martínez Pascual et al55
Mandibular 0.80 ± 0.34 Martínez Pascual et al55
Cervical 0.83 ± 0.15 Martínez Pascual et al55
IX-X-XI nerves
 Glossopharyngeal nerve Midcervical Not available
 Vagus nerve Midcervical 5.1 ± 1.5 Hammer et al56
 Accessory nerve Midcervical Not available
Hypoglossal nerve
 Segment Proximal 1.41 ± 1.01 Vacher et al57
Above greater horn of hyoid 1.23 ± 0.77 Vacher et al57
Cervical loop 0.48 ± 0.26 Vacher et al57
Occipital nerves
 Greater occipital nerve After exiting the semispinalis capitis muscle 3.8 ± 1.6 Ducic et al58
 Lesser occipital nerve Posterior border of sternocleidomastoid msucle 1.2 ± 1.6 Ducic et al58
 Third occipital nerve After exiting the trapezius muscle 1.5 ± 0.3 Tubbs et al59

MRN, magnetic resonance neurography.