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| LEVEL | CRANIAL | CAUDAL | ANTERIOR |
POSTERIOR | LATERAL | MEDIAL |
| Ia | Geniohyoid m., plane tangent to basilar edgeof mandible | Plane tangent to body of hyoid bone | Symphysis menti, platysma m. |
Body of hyoid bone | Medial edge of ant. belly of digastric m. | n.a.a |
| Ib | Mylohyoid m., cranial edge of submandibular gland | Plane through central part of hyoid bone | Symphysis menti, platysma m. |
Posterior edge of submandibular gland | Basilar edge / innerside of mandible, platysma m., skin | Lateral edge of ant. belly of digastric m. |
| IIa | Caudal edge of lateral process of C1 | Caudal edge of the body of hyoid bone | Post. edge of submandibular gland; ant. edge of int. carotid artery; post. edge of post. belly of digastric m. |
Post. Border of int. jugular vein | Medial edge of sternocleidomastoid | Medial edge of int. carotid artery, paraspinal (levator scapulae) m. |
| IIb | Caudal edge of lateral process of C1 | Caudal edge of the body of hyoid bone | Post. Border of int. jugular vein |
Post. border of the sternocleidomastoid m. | Medial edge of sternocleidomastoid | Medial edge of int. carotid artery, paraspinal (levator scapulae) m. |
| III | Caudal edge of the body of hyoid bone | Caudal edge of cricoid cartilage | Postero-lateral edge of the sternohyoid m.; ant. edge of sternocleidomastoid m. |
Post. edge of the sternocleidomastoid m. | Medial edge of sternocleidomastoid | Int. edge of carotid artery, paraspinal (scalenius) m. |
| IV | Caudal edge of cricoid cartilage | 2 cm cranial to sternoclavicular joint | Anteromedial edge of sternocleido-mastoid m |
Post. edge of the sternocleidomastoid m. | Medial edge of sternocleidomastoid | Medial edge of internal carotid artery, paraspinal (scalenius) m. |
| V | Cranial edge of body of hyoid bone | CT slice encompassing the transverse cervical vesselsb | Post. edge of the sternocleidomastoid m. |
Ant. border of the trapezius m. | Platysma m., skin | Paraspinal (levator scapulae, splenius capitis) m. |
| VI | Caudal edge of body of thyroid cartilagec | Sternal manubrium | Skin; platysma m. |
Separation between trachea and esophagusd | Medial edges of thyroid gland, skin and ant.-medial edge of sternocleidomastoid m. | n.a. |
| Retro- pharyngeal | Base of skull | Cranial edge of the body of hyoid bone | Fascia under the pharyngeal mucosa |
Prevertebral m. (longus colli, longus capitis) | Medial edge of the internal carotid artery | Midline |
a Midline structure lying between the medial borders of the anterior bellies of the digastric muscles
b for NPC, the reader is referred to the original description of the UICC/AJCC 1997 edition of the Ho's triangle. In essence, the fatty planes below and around the clavicle down to the trapezius muscle.
c for paratracheal and recurrent nodes, the cranial border is the caudal edge of the cricoid cartilage.
d for pretracheal nodes, trachea and anterior edge of cricoid cartilage
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