Radiological approach to neck spaces

Anatomy of neck space by Dr. Milan

1. Radiological A pproach to Neck Spaces Dr. Milan Silwal Resident, Radiodiagnosis

2. Background: Head and neck lesions are a very challenging subject due to the complex anatomy and wide ranging pathology. Cross sectional imaging is commonly used for clinical evaluation of head and neck lesions. The anatomical location and borders of head and neck lesions are vital in narrowing radiological differential diagnosis and allowing formation of an appropriate clinical management plan.

3. Neck Spaces: Described in relation to the hyoid Suprahyoid (SHN) Infrahyoid (IHN)

4. Fascia of the neck Key to understanding neck spaces is fascia. 2 major fascial layers of the neck: superficial and deep cervical fascia.

5. Deep cervical fascia comprises three distinct layers: Superficial layer splits to enclose a number of muscles (including sternomastoid and trapezius) and contributes to formation of the carotid sheath. Middle layer envelops the anterior infrahyoid strap muscles, and splits to enclose the contents of the visceral space. It forms the anterior wall of the retropharyngeal space and contributing to formation of the carotid sheath. Deep layer encircles the paraspinous and prevertebral muscles and associated structures. Attaching to the transverse processes, the deep layer subdivides the perivertebral space into the prevertebral space and the paraspinal space

6. PPS lies in a central location in the deep face PMS is medial to the PPS MS is anterior to the PPS PS is lateral of the PPS CS is posterior to the PPS RPS is posterior to PPS P erivertebral space is posterior to the RPS

7. Axial graphic depicting the fascia and spaces of the infrahyoid neck. The three layers of deep cervical fascia are present in the suprahyoid and infrahyoid neck. The carotid sheath is made up of all 3 layers of deep cervical fascia (tri-color line around carotid space). Notice the deep layer completely circles the perivertebral space, diving in laterally to divide it into prevertebral and a paraspinal components.

8. Graphic of skull base from below shows spaces of suprahyoid neck relationships to skull base. Four spaces have key interactions with skull base, masticator, parotid, carotid and pharyngeal mucosal spaces. PS (green) malignancy can follow CN7 into stylomastoid foramen. MS (purple) receives CNV3 while CN9-12 enter the CS (red). The PMS abuts the foramen lacerum , which is covered by fibrocartilage in life. Also note that the superficial layer of deep cervical fascia (yellow line) surrounds the MS & PS and middle layer is on non-airway side of PMS (pink line).

9. Coronal graphic of parapharyngeal space. The parapharyngeal spaces are paired fat-filled spaces in the more lateral aspect of the suprahyoid neck. This space abuts the skull base between the masticator and pharyngeal mucosal spaces. There are no important structures at the point of intersection between the PPS and the skull base. Inferiorly the PPS communicates inferiorly with the posterior submandibular space. The masticator space has the largest area of abutment with the skull base, including CNV3. The pharyngeal mucosal space abuts the basisphenoid and foramen lacerum .

10. Deep neck spaces suprahyoid neck parapharyngeal space parotid space pharyngeal mucosal space masticator space buccal space infrahyoid neck anterior cervical space posterior cervical space visceral space supra- and infrahyoid neck carotid space retropharyngeal space perivertebral space

11. Parapharyngeal space PPS : Central, fat-filled spaces in lateral suprahyoid neck (SHN) around which most of important spaces are located. Is shaped like a pyramid, inverted with its base at the skull base, with its apex inferiorly pointing to the greater cornu of the hyoid bone.

12. Importance of PPS is its conspicuity on CT and MR as well as its direction of displacement by mass lesions of surrounding spaces PPS displacement pattern helps define actual space of origin PMS mass lesion pushes PPS laterally MS mass lesion pushes PPS posteriorly PS mass lesion pushes PPS medially CS mass lesion pushes PPS anteriorly

13. Boundaries superior margin: base of skull inferior margin: greater cornu of hyoid bone medial margin:  pretracheal layer of the deep cervical fascia lateral margin: investing fascia of the deep cervical fascia covering the deep lobe of the parotid anterior margin: investing fascia of the deep cervical fascia covering the medial pterygoid muscle posterior margin: prevertebral layer of the deep cervical fascia

14. Contents fat (main component) internal maxillary artery ascending pharyngeal artery pterygoid venous plexus only small portion; mainly within masticator space lymph nodes

15. This image at the level of the nasopharynx shows the four key spaces surrounding the parapharyngeal space, the pharyngeal mucosal, masticator, parotid and carotid spaces.

16. Related pathiologies in PPS : benign mixed tumor (from minor salivary gland rests in PPS), lipoma atypical second branchial cleft cyst. parapharyngeal cellulitis /  parapharyngeal abscess trigeminal schwannoma To say lesion is primary to PPS, it must be completely surrounded by PPS fat In most cases where lesion is thought to be primary to PPS, careful observation will find connection to one of surrounding spaces (usually PS)

17. Pharyngeal mucosal space Anatomy Relationships Airway side of PMS has no fascial border Posterior to PMS is retropharyngeal space RPS Lateral to PMS is PPS

18. Internal Contents Mucosal surface of pharynx PMS lymphatic ring : Lymphatic ring of tissue of PMS ( Waldeyer ring) Nasopharynx : Adenoids Oropharynx , lateral wall: Palatine ( faucial ) tonsil Oropharynx , base of tongue: Lingual tonsil Minor salivary glands Soft palate mucosa has highest concentration Pharyngobasilar fascia Tough aponeurosis that connects superior constrictor muscle to skull base Posterosuperior margin notch = sinus of Morgagni Levator palatini muscle & eustachian tube pass through this notch on way from skull base to PMS

19. Lesion is designated primary to PMS under following circumstances Lesion center is medial to parapharyngeal space mass pushes PPS fat from medial to lateral mass disrupts normal PMS mucosal & submucosal architecture

20. MASTICATOR SPACE MS is large SHN space spanning area from high parietal calvarium ( suprazygomatic MS) above to mandibular angle below Suprazygomatic MS : Contains only belly of temporalis muscle Infrazygomatic MS : MS "proper"; containing masseter , medial & lateral pterygoids , CNV3 & ramus /posterior body of mandible

21. Craniocaudal extent of MS is more extensive than commonly recognized On its cephalad margin MS reaches high on parietal calvarium at top of suprazygomatic MS Abuts skull base with foramen ovale & foramen spinosum included MS lesions displace PPS from anterior to posterior Masticator space malignancy can spread perineurally via the mandibular division of the trigeminal nerve into the middle cranial fossa .

22. BUCCAL SPACE BS is pyramidal fat-filled space of midface ; forms padding of cheeks No defined fascial boundaries BS predominantly fat & small nodes Parotid duct traverses BS; pierces buccinator at level of upper 2nd molar Accessory parotid gland found in ≈ 20% Majority of BS pathology is nodal disease or extension of pathology from adjacent structures & spaces

23. Related pathology parotid duct calculi odontogenic infection tumours : minor salivary gland tumours , vascular lesions ( eg haemangiomas )

24. PAROTID SPACE Paired lateral suprahyoid neck spaces enclosed by superficial layer of deep cervical fascia containing parotid glands, nodes & extracranial facial nerve branches PS extends from external auditory canal (EAC) & mastoid tip superiorly to angle of mandible (parotid tail ) below features to define a primary parotid space lesion : Center of lesion is within parotid gland If larger mass lesion of deep lobe, mass displaces PPS from lateral to medial with widening of stylomandibular gap

25. Boundaries superior margin: external auditory canal; apex of the mastoid process inferior margin: inferior mandibular margin anterior margin: masticator space Contents  parotid glands intraparotid lymph nodes intraparotid facial nerve (CN VII) external carotid artery (ECA) retromandibular vein

26. Related pathology congenital  agenesis first branchial cleft cyst hemangioma cystic hygroma / lymphangioma  salivary gland tumours -benign and primary malignant tumour metastatic adenopathy lymphoma parotid cysts inflammatory sialadenitis abscess Sjogren's syndrome

27. Clinical Importance Intraparotid facial nerve although invisible to imaging is key PS structure Try to assess relationship of mass lesion to estimated facial nerve plane (lateral to retromandibular vein) Superficial, deep or in plane of intraparotid CN7? Evidence of perineural tumor affecting CN7?

28. CAROTID SPACE Paired, tubular spaces surrounded by carotid sheath that contain carotid arteries, internal jugular veins, cranial nerves (CN) 9-12 (SHN) & CN10 (IHN) extends from skull base (carotid canal and jugular foramen) to aortic arch below divided into its major segments Nasopharyngeal, oropharyngeal , cervical and mediastinal segments

29. Boundaries superior margin: lower border of jugular foramen inferior margin: aortic arch anterolateral margin: sternocleidomastoid muscle

30. CAROTID SPACE The suprahyoid carotid space contains CN9-12, the internal carotid artery & the internal jugular vein. The carotid sheath is made up of components of all 3 layers of deep cervical fascia (tri-color line around carotid space). In the suprahyoid neck the carotid sheath is less substantial than in the infrahyoid neck. The sympathetic trunk runs just medial to the carotid space.

31. Paraganglioma : T1-weighted Gadolineum enhanced MR image at the level of the supraglottic larynx

32. CS mass displacement pattern Nasopharyngeal CS mass: PPS displaced anteriorly, styloid process displaced anterolaterally Oropharyngeal CS mass: PPS displaced anteriorly, posterior belly of digastric displaced laterally Infrahyoid neck CS mass: Surrounds CCA May separate CCA from IJV

33. RETROPHARYNGEAL SPACE RPS is fat-filled space in posterior midline of neck that can be identified on imaging from skull base to upper mediastinum Upper-most RPS (nasopharyngeal portion) is “narrow" In RPS abscess path of least resistance is inferiorly RPS nodes only found in suprahyoid neck

34. Pharyngeal mucosal space (PMS) is anterior Danger space (DS) is directly posterior to RPS Carotid space is lateral to RPS Fat is primary occupant of SHN RPS RPS lymph nodes Lateral group :Also called nodes of Rouviere Medial group : Less often visible on imaging

35. radiologic findings to define a lesion as primary to RPS: Centered posteromedial to parapharyngeal space (PPS) & directly medial to carotid space Encroaches on PPS from posteromedial to anterolateral

36. Retropharyngeal space (RPS) is immediately posterior to pharynx & anterior to prevertebral muscles Distension of space results in biconvex, bow tie, or oval configurations Plain film cannot distinguish RPS from prevertebral space process Consider abscess 1st in differential of low density RPS mass Delay in diagnosis and treatment can have grave consequences Airway compromise Abscess spreads to danger space and then mediastinum

37. Danger space Danger space  is a potential space located behind the true retropharyngeal space, which connects the deep cervical spaces to the  mediastinum. Boundaries: anteriorly -  alar fascia posteriorly -  prevertebral fascia superiorly - extends from the clivus inferiorly - posterior mediastinum at the level of the diaphragm

38. It is a potential path for spread of infections from the pharynx to the mediastinum. In healthy patients, it is indistinguishable from the  RPS. It is only visible when distended by fluid or pus, below the level of T1-T6, since the retropharyngeal space variably ends at this level . Expected location of the danger space (green)

39. Perivertebral space Cylindrical space surrounding vertebral column extending from skull base to upper mediastinum bounded by deep layer, deep cervical fascia subdivided into prevertebral & paraspinal components Prevertebral -PVS sits directly behind retropharyngeal space Paraspinal -PVS is deep to posterior cervical space & posterior to transverse processes of cervical spine

40. Imaging findings to define a mass lesion as primary to prevertebral -PVS: Mass is centered within prevertebral muscles or corpus of vertebral body Mass lifts prevertebral muscles anteriorly (RPS mass pushes them posteriorly ) Most PVS lesions originate in vertebral body (infection or metastatic tumor ) or Vertebral body is usu. Involved when PVS lesion is found

41. Prevertebral -PVS disease may involve epidural space 1st barrier to spread is deep layer of deep cervical fascia Path of least resistance of spreading pus or tumor is deep through neural foramen into epidural space When prevertebral PVS disease is found on imaging, always check for epidural space extension!

42. Infrahyoid neck space

43. Infrahyoid neck space The infrahyoid neck is divided into 6 anatomical compartments or spaces by the various layers of the cervical fascia. These spaces are well recognized in the axial plane and therefore suited for analysis on axial CT or MR.

44. Visceral space Location: anterior, within the middle layer of deep cervical fascia. Contents: Thyroid & parathyroids , paratracheal nodes, esophagus, trachea, recurrent laryngeal nerve Importance: Trachea & esophagus traverse Visceral space

45. Multinodular goiter The swelling is adjacent to the left lamina of the thyroid cartilage . The strap musculature seems to be draped over the lesion (blue arrow ). Therefore this lesion lies within the visceral space.

46. Anterior cervical space and posterior cervical spaces: They are predominantly fat filled, so these spaces typically provide symmetric imaging landmarks on axial imaging. Posterior cervical space contain CN XI. Posterior cervical space contains the spinal accessory lymph node chain also, so it is commonly affected by both inflammatory and malignant nodal disease

47. Anterior cervical space small infrahyoid compartment of the head and neck. It is not enclosed by fascia. Contents- areolar fat Related pathology lipoma (most common)  second branchial cleft cysts

48. The mass has the signal intensity of fat on a T1-weighted image and the signal is completely suppressed with fat suppression.

49. To conclude: Head and neck anatomy is described reflecting the importance of fascia lined spaces in confining various pathologies. Neck has been divided into a number of 'deep spaces‘; suprahyoid and infrahyoid with some of the spaces having continuation in both the region. Knowledge of neck spaces allows for better communication and aids in diagnosis as each space has a distinct group of pathologies. 

50. References: Textbook of Radiology and Imaging-David sutton Head and neck spaces: Where and what? By K. J. Au Yong et al; doi : 10.1594/ecr2009/C-468 Radiology Assistant

51. Thank You!