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CLINICAL REVIEW David W. Eisele, M.D., Section Editor Head and neck fascia and compartments: No space for spaces Alice K. Guidera, BSc, MBChB,1* Patrick J. D. Dawes, MBChB, FRCS,1 Amy Fong, MBBS, FRANZCR,2 Mark D. Stringer, MS, FRCS,3 1 Department of Surgical Sciences, Dunedin School of Medicine, Dunedin, New Zealand, 2Department of Radiology, Southern DHB, Dunedin, New Zealand, 3Department of Anatomy, Otago School of Medical Sciences, University of Otago, Dunedin, New Zealand. Accepted 24 July 2013 Published online 29 January 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/hed.23442 ABSTRACT: An accurate understanding of the arrangement of cervical fascia and its associated compartments is essential for differential diagnosis, predicting the spread of disease, and surgical management. The purpose of this detailed review is to summarize the anatomic, clinical, and radiological literature to determine what is known about the arrangement of cervical fascia and to highlight controversies and consensus. The current terminology used to describe cervical fascia and compartments is replete with confusing synonyms and inconsistencies, creating important interdisciplinary differences in understanding. The term ‘‘spaces’’ is inappropriate. A modified nomenclature underpinned by evidence-based anatomic and radiologic findings is proposed. This should not only enhance our understanding of cervical anatomy but also C facilitate clearer interdisciplinary communication. V 2014 Wiley Periodicals, Inc. Head Neck 36: 1058–1068, 2014 INTRODUCTION A contributing factor is the variability of what is meant by ‘‘fascia.’’ Definitions usually refer to an organized arrangement of connective tissue that can be discerned macroscopically.6–9 This is often limited to the fibrous connective tissue that forms sheets or sheaths around structures,7,10 but the International Fascia Research Congress recently broadly redefined fascia as ‘‘the soft tissue component of the connective tissue system that permeates the human body’’ including ‘‘all fibrous connective tissues, aponeuroses, ligaments, tendons, retinaculae, joint capsules, organ and vessel tunics, the epineurium, the meninges, the periostea, and all the endomysial and intermuscular fibers of the myofasciae.’’10 The classification of fascia is similarly variable with groupings based on developmental origin, function, or appearance.9,11–13 Fascia can vary between individuals according to mechanical stress, age, and disease processes.14–16 This report reviews historic and modern anatomic, clinical, and radiologic studies of head and neck fascia with the purpose of identifying areas of consensus and controversy. A modified nomenclature that has the potential to encourage greater cross-disciplinary understanding of head and neck fasciae and its associated compartments is proposed. Historically, anatomic and clinical studies have described cervical fascia in the context of the spread of infection and surgical management of disease.1,2 These provided the foundation for modern radiology texts that focus on the contents of named ‘‘spaces,’’ which is essential in differential diagnosis.3,4 However, as surgical technology advances, a more precise understanding of fascial arrangements and their variations becomes imperative. For example, endoscopic and robotic surgery offer access to previously inaccessible areas and provide new approaches to standard procedures with reduced morbidity. A recent review of recommended texts for radiology and surgery trainees and students of anatomy highlighted widespread confusion about both the layers of cervical fascia and their potential spaces.5 Not only were descriptions of fascial arrangements and definitions of spaces inconsistent and unclear, but the terminology was variable and open to misinterpretation. The names used to describe the fascial layers around the parapharyngeal, submandibular, and visceral spaces were particularly confusing. KEY WORDS: head, neck, fascia, anatomy, terminology METHODS *Corresponding author: A. K. Guidera, Department of Surgical Sciences, Dunedin School of Medicine, PO Box 913, Dunedin 9054, New Zealand. E-mail: [email protected] Contract grant sponsor: This review was completed as part of ongoing research funded by The Foundation for Surgery Research Scholarship, Royal Australasian College of Surgeons; a Dunedin School of Medicine Clinical Research Scholarship, University of Otago; and The Richard Stewart Scholarship awarded by The Dunedin Basic Medical Sciences Course Trust, Dunedin School of Medicine, University of Otago. 1058 HEAD & NECK—DOI 10.1002/HED JULY 2014 An Ovid MEDLINE (1946–July 2012) search was conducted using the MeSH terms: ‘‘fascia,’’ ‘‘neck,’’ and ‘‘anatomy,’’ ‘‘radiology’’ or ‘‘surgery,’’ and keywords ‘‘deep cervical fascia,’’ ‘‘cervical fascia,’’ ‘‘prevertebral fascia,’’ ‘‘pretracheal fascia,’’ ‘‘investing fascia,’’ and ‘‘superficial cervical fascia.’’ Further searches were conducted using the keywords ‘‘masticator space,’’ ‘‘submandibular space,’’ ‘‘retropharyngeal space,’’ HEAD ‘‘parapharyngeal space,’’ ‘‘lateral pharyngeal space,’’ ‘‘prevertebral space,’’ ‘‘visceral space,’’ and ‘‘deep neck space,’’ all limited to ‘‘human.’’ Relevant original research articles were supplemented by additional references obtained from article reference lists. Illustrations were created in Adobe Illustrator (CS5.1) from 2 sources: plastinated E12 axial slices (2.5-mm thickness) through the head and neck of a 65-year-old female cadaver available through the W.D. Trotter Anatomy Museum at the University of Otago; and from anonymized normal MRIs obtained after institutional ethics committee approval (LRS/11/EXP/013). Layers of cervical fascia For the purposes of this review, discussion is limited to fascia that is traditionally described as delineating potential spaces within the head and neck. The pharyngobasilar fascia and fasciae that might otherwise be regarded as a tendon or ligament are not included. Superficial cervical fascia The variable definition of fascia is the root of much of the confusion surrounding the superficial cervical fascia (SCF). Some authors describe this as a continuous sheet of fascia extending from the head and neck to the thorax and axillae,1,2,17 whereas others use the term to indicate a layer indistinguishable from,18 or synonymous with,19,20 the subcutaneous fat. The term ‘‘superficial cervical fascia’’ has been removed from the current reference source on anatomic nomenclature because it no longer represents a standard description.9 In the neck, the SCF contains the platysma and superficial lymph nodes1,18,19,21,22 and is loosely arranged to facilitate neck movement. Craniad to the mandible, the SCF continues as the fascia that ‘‘invests’’ the muscles of facial expression and occipitofrontalis in the scalp1,19,23; it is referred to by different names as it progresses cranially.24 Interest in this layer was renewed with the popularization of facelift surgery and the definition of the superficial musculoaponeurotic system (SMAS).22,25–27 Starting at the vertex, the galea aponeurotica, occipitofrontalis, and orbicularis oculi muscles are in continuity with the temporoparietal fascia24,28 and, inferior to this, the SMAS over the zygomatic arch25,28 (although not all authorities agree on the latter).8 This layer, which incorporates the muscles of facial expression, is then continuous with the SCF and platysma in the neck.26,29,30 Beneath the temporoparietal fascia is a layer of loose but vascular connective tissue often called the innominate fascia by plastic surgeons31; this is continuous with the subgaleal layer in the scalp but its limits are not well described. The relationship between the SMAS and the SCF is contentious: descriptions range from the two being synonymous,26,32 related,33 distinct,27 or there being no such layer as the SMAS as originally defined by Mitz and Peyronie.22,25,29 These predominantly histologic studies have also suggested that the SCF (rather than the superficial layer of deep cervical fascia) forms the lateral fascial layer over the parotid.26,29,30 AND NECK FASCIA AND COMPARTMENTS ‘‘completely encircling the neck,’’1,17–19,21,24,34 although it has been suggested that it is incomplete between the sternocleidomastoid and trapezius muscles.35,36 A simplified ‘‘rule of twos’’ describes the SLDCF as enclosing 2 glands (submandibular and parotid), 2 muscles (sternocleidomastoid and trapezius), and 2 ‘‘spaces’’ (suprasternal space and the ‘‘subvaginal’’ space of the posterior triangle).17,19,34 The relationship between the SLDCF and the middle layer of deep cervical fascia (MLDCF) is variously described. Some authors report that they are fused at several sites: at the hyoid; along the superolateral border of the anterior belly of omohyoid continuing along its posterior belly into the posterior triangle; where the MLDCF covers the sternothyroid and thyrohyoid1; and with the buccopharyngeal fascia.23 Superior to the hyoid, the SLDCF attaches to the mandible and styloid process, fusing with the sheath around the digastric, and splitting to enclose the submandibular gland separating it from hyoglossus and the superior constrictor muscle on its deep surface1; a thickening of this layer contributes to the stylomandibular ligament.17,37,38 Superior to the mandible, the SLDCF splits into 2 laminae, the lateral lamina covering the masseter and attaching to the zygomatic arch1,39 and the medial lamina running on the deep surface of the pterygoid muscles and attaching to the skull base medial to the foramen ovale.1,23,38–41 The most cranial extension of the SLDCF is disputed. Some authors refer to the temporal fascia that extends up over the temporalis to attach to the superior temporal line8,42 as a continuation of the SLDCF,1,23,39,41,43 whereas others limit the superior extent to the zygoma18,34,39,44 or extend it into the aponeurotic layer of the scalp.23 There is also debate about whether the SLDCF completely invests the parotid gland26,29,30 and its relationship to the masseteric fascia.1,23,39 This is not a new argument.43 More recent studies suggest that the SLDCF is continuous with the fascia covering the masseter muscle but that the parotid gland lies laterally and is covered with fascia of a different origin, variably described as SCF, innominate fascia,31 or a ‘‘platysmal’’ layer.22,27,29,30 Middle layer of deep cervical fascia. This is described as having muscular and visceral divisions1,2,17,19,34,37,38 or simply a visceral part.18,39,44–46 Muscular layer. This term is usually used in conjunction with ‘‘visceral fascia’’ to describe that portion of the MLDCF that ensheaths the strap muscles.17,19,47 Some authors subdivide it into sternohyoid/omohyoid and sternothyroid/thyrohyoid components,1,47 whereas others refer to it generally as the ‘‘strap fascia,’’35 or even part of the SLDCF.21,34 This layer runs between the bony attachments of these muscles. Deep cervical fascia Visceral layer. This has been used to describe all the components of the MLDCF19 or only that part surrounding the larynx, pharynx, trachea, esophagus, and thyroid.1,18 The latter is generally agreed to blend inferiorly with the fibrous pericardium1,17–19,34,37,38,44 but there is disagreement as to whether it extends superiorly only to the level of the hyoid bone34,38,44 or if a posterior continuation reaches the skull base.1,17–19,39,47 Superficial layer of deep cervical fascia. The superficial layer of deep cervical fascia (SLDCF) is usually described as Buccopharyngeal fascia. The prefix ‘‘bucco’’ refers to the superior extension of this layer that is stated to continue HEAD & NECK—DOI 10.1002/HED JULY 2014 1059 GUIDERA ET AL. TABLE 1. Historical and suggested terms for the cervical fascia. Layer Other terms SCF DCF Superficial layer Middle layer Deep layer Suggested term Galea aponeurotica, temporoparietal fascia, superficial temporal fascia, subcutaneous tissue, platysmal layer, and subcutaneous musculoaponeurotic system Subcutaneous tissue Subaponeurotic layer of galea aponeurotica, parotidomasseteric fascia Investing fascia, enveloping layer, general or deep investing fascia, great cervical sheath, external layer, and anterior layer29,30 Muscular division Sterno-omohyoid layer Sternothyroid-thyrohyoid layer Visceral fascia, pretracheal fascia, prethyroid fascia, and buccopharyngeal fascia Pharyngomucosal fascia Prevertebral, perivertebral, and paravertebral Scalene fascia Alar fascia Masticator fascia Submandibular fascia Sternocleidomastoid-trapezius fascia Strap muscle fascia Visceral fascia Perivertebral fascia (prevertebral for anterior part only) Alar fascia Abbreviations: SCF, superficial cervical fascia; DCF, deep cervical fascia. over the buccinator muscle.19 This term has been used to refer to the whole ‘‘visceral’’ component of the MLDCF,1,4,17,39,48 or to a discrete entity that is adherent to the pharynx and either continuous with,1,46 or separate from23,34 the MLDCF. Pretracheal fascia. This term is rarely used in isolation. With the exception of 1 reference restricting the term to that portion of the MLDCF lying anterior to the trachea,34 ‘‘pretracheal’’ was synonymous with the MLDCF surrounding the larynx, pharynx, trachea, esophagus, and thyroid.1,17,34,44 Other terms in the literature include the ‘‘pharyngomucosal fascia’’ to describe the purely visceral portion of the MLDCF45 and the ‘‘viscerovascular system’’ of fascia to describe the fascia surrounding the viscera of the neck and the carotid sheath.43,47 Deep layer of deep cervical fascia This is consistently described as encompassing the vertebral column and paravertebral muscles, attaching to the transverse and spinous processes of the cervical vertebrae.1,2,17,39 As it passes laterally over the scalene muscles, it forms the floor of the posterior triangle. The term ‘‘prevertebral’’ is used to describe either the complete circumferential layer of fascia2,45 or just that part covering the prevertebral muscles anteriorly between the transverse processes.1,21,34,37,38 Laterally, it is described as being continuous with the axillary sheath and the suprapleural membrane (Sibson’s fascia). Caudally, it is stated to extend to the coccyx1,2,17,19 or ‘‘fades away’’ in the thorax.34 The alar fascia is generally stated to be a division of the deep layer of deep cervical fascia (DLDCF) spanning between the transverse processes of the cervical vertebrae anterior to the prevertebral fascia and fusing laterally with the carotid sheath.1,2,17,19,21 Carotid sheath Modern radiologic and surgical sources frequently describe the carotid sheath as being composed of all 3 1060 HEAD & NECK—DOI 10.1002/HED JULY 2014 layers of DCF,4,20,39,41,49–52 but offer little explanation as to how this occurs. In their seminal article in 1938, Grodinsky and Holyoke1 suggested that the carotid sheath receives contributions from the alar fascia (DLDCF) throughout its length, from the SLDCF adjacent to the digastric and sternocleidomastoid muscles, and from the MLDCF where it covers the sternothyroid. A few authors offer alternative descriptions stating that the carotid sheath is made up of the SLDCF and pretracheal layers of fascia,53 or is independently derived but receives a contribution medially from the alar fascia.45 Older literature contains even more diverse statements about the composition of the carotid sheath.18,37,47,54 Histologic studies have found that the carotid sheath is always present in its upper third55 and distinct from other fascial layers.15 The thickness of the carotid sheath varies between individuals and at different levels in the neck.15 It seems to form a barrier to metastatic disease.56 It is developmentally distinct from the prevertebral fascia and is intimately related to the fascia enclosing omohyoid14 and the visceral compartment15 in part of its course. Recommendations on cervical fascia The terms ‘‘superficial’’, ‘‘middle’’, and ‘‘deep’’ layers of cervical fascia are confusing and should be abandoned for several reasons. First, the term ‘‘superficial fascia’’ is poorly defined and variably applied.7,9,12,31,57,58 It can refer to the layer of fatty connective tissue immediately deep to the dermis,12 or more specifically to a membranous layer within the fatty subcutaneous tissue.59 Second, there is obvious confusion in having a term that contains more than 1 descriptor (eg, ‘‘superficial’’ and ‘‘deep’’). Third, the ‘‘middle’’ layer is actually anterior to the ‘‘deep’’ layer, which, in places, is relatively superficial. Finally, these terms imply distinct fascial layers that are independent of each other, whereas at some sites they are closely associated and even fused. Adopting the following terms (Table 1) may reduce confusion: HEAD ‘‘Superficial fascia’’ should be replaced by ‘‘subcutaneous tissue’’ as recommended in Terminologia Anatomica9; in many regions, this may contain a readily identifiable membranous layer and/or cutaneous muscles. Although there is some debate about the existence of SMAS, it seems to be a feature of this layer but its relationship to the parotid gland is controversial. Fascia that invests muscle is best described according to its related functional muscle group. Thus, the masticator fascia covers the muscles of mastication (and therefore includes the temporal, masseteric, and pterygoid fasciae) and defines the boundaries of the masticator space. The strap muscle fascia invests sternohyoid, thyrohyoid, sternothyroid, and omohyoid and can be distinguished from both the fascia of the overlying sternocleidomastoid and that surrounding the underlying visceral and carotid compartments, although they may be adherent in places.1,14 The fascia of the styloid muscles and posterior belly of digastric is often ignored in discussions of the DCF, but the proposed classification would allow this fascia to be called the ‘‘styloid fascia.’’ This scheme would also recognize the sternocleidomastoid-trapezius fascia as investing these muscles and bridging the gap anteriorly between the sternocleidomastoid muscles; until the controversy about whether this fascia bridges the posterior triangle is resolved, there is no need to consider revising this to separate sternocleidomastoid and trapezius fasciae.35,36 The fascia passing between the hyoid and the mandible that splits to encompass the submandibular gland and forms the floor of the submandibular space would be called the ‘‘submandibular fascia’’ (distinct from the capsule of the submandibular gland). The terms ‘‘pretracheal’’ and ‘‘buccopharyngeal’’ are ambiguous and anatomically imprecise and should be abandoned. The fascia surrounding the larynx/trachea, pharynx/esophagus, and thyroid should be designated ‘‘visceral fascia.’’ The confusion surrounding the extent of the ‘‘DLDCF’’ seems to be limited to texts.5 In the anatomic literature, this layer extends between the transverse processes of the cervical vertebrae anterior to the prevertebral muscles, is continuous laterally with the scalene fascia, and extends posteriorly to reach the cervical spinous processes. Because this layer surrounds the vertebral column and its musculature, the term ‘‘perivertebral fascia’’ would be more appropriate for fascia lateral and posterior to the transverse processes45,52,53 with prevertebral fascia defining the fascia on the anterior surface of the prevertebral muscles. The term ‘‘alar fascia’’ can be retained to describe the discrete layer of fascia immediately anterior to the prevertebral fascia spanning between the transverse processes of the cervical vertebrae. The carotid sheath surrounds the internal carotid artery, internal jugular vein, and lower cranial nerves. It is connected to and reinforced by adjacent fascia at different sites (eg, the alar, visceral, and strap muscle fascia). Fascial ‘‘spaces’’ and planes Defining ‘‘spaces’’ in the head and neck is similarly prone to misinterpretation and confusion. The Oxford English Dictionary defines a space as ‘‘a continuous area AND NECK FASCIA AND COMPARTMENTS or expanse that is free, available, or unoccupied.’’60 In the neck, a ‘‘space’’ may refer to a functional unit,2,50,52,53 or anatomic region bounded by fascia,39,61–63 or a region bounded by bones, muscles, fascia, or skin.23 With advances in radiology, ‘‘spaces’’ have often been defined by their anatomic contents (eg, blood vessels, lymph nodes, nerves, and viscera) rather than their fascial perimeters, and have tended to become regions containing a set of defined structures easily identifiable on crosssectional imaging.41,53 Most ‘‘spaces’’ in the body are in fact either ‘‘potential spaces’’2,23,64,65 or 19,37,38 compartments. For discussion purposes, ‘‘spaces’’ in the head and neck can be roughly divided into cranial (related to the skull and face) and cervical (related to the cervical spine), although these distinctions are not absolute. Cranial fascial ‘‘spaces’’ The cranial fascial ‘‘spaces’’ include the spaces related to the parotid gland, muscles of mastication, and the submandibular gland. Parotid space. The term ‘‘parotid space’’ is used almost exclusively in the radiologic literature.41,45,66,67 It describes the potential space created by the fascia that encloses the parotid gland,4,39,41,66,67 although, as noted previously, the precise fascial arrangement in this area is debatable.22,29 The deep lobe of the parotid gland extends posteromedial to the mandible and forms a lateral border of the parapharyngeal space. Although anatomic studies suggest that the fascia covering this aspect of the parotid is complete,1 the spread of infection from the parotid to the parapharyngeal space noted in the clinical literature indicates that it does not provide a functional barrier.43,67 Masticator space. This was originally defined as a discrete region limited by the masseter, pterygoid, and temporal muscles in continuity with but not including the superficial and deep temporal spaces. Some anatomic studies have taken the zygomatic arch as the superior extent of this space but agree that there is free communication with the superficial and deep temporal spaces.1,2,23,43 Other studies have referred to a single masticator space that also includes the buccal fat pad anterolaterally,68,69 or subdivided the space into suprazygomatic, retrozygomatic, infratemporal, and nasopharyngeal regions.4,19,23,39,45,50,61 Superficial and deep temporal spaces. The superficial temporal space is the space between the temporal fascia covering the temporalis and the temporoparietal fascia. The deep temporal space lies between the temporalis, the periosteum of the temporal bone, and the lateral pterygoid muscle.17,43 Both spaces freely communicate anteriorly and the deep temporal space communicates with the masticator space. Infratemporal space (fossa). To anatomists, this is the postmaxillary region between the ramus of the mandible laterally and the pharyngeal wall medially inferior to the zygomatic arch.8 Various boundaries delimited by muscles and the parotid gland are described in the clinical literature70–75 with some radiologists choosing to include HEAD & NECK—DOI 10.1002/HED JULY 2014 1061 GUIDERA ET AL. both the masticator and parotid spaces as subdivisions of this fossa.76 Buccal space. Originally described as the space occupied by the buccal fat pad anterior to the masseter muscle,23 it has often been neglected in discussions of spaces in the head and neck. The buccal space is bordered anterolaterally by subcutaneous tissue and the zygomaticus major, minor, and risorius muscles,23,41,77 medially by the buccinator, and posteriorly by the mandible, masseter, and pterygoid muscles. Continuity of the buccal fat pad with the temporoparietal fat pad is well described.23,41,45,68,69,77 Infection in this region is stated to always involve the masticator compartment,66 and, although clinical studies report early confinement of infection, spread into the parotid, temporal, and submandibular spaces occurs with disease progression.61,69 Submandibular space. This term (and the archaic ‘‘submaxillary space’’) has been used to describe 2 different anatomic regions: first, the space inferior to the mylohyoid bounded inferiorly by the attachment of the SLDCF between the mandible and hyoid41,45; and second, the space superior and inferior to the mylohyoid, including the floor of mouth.1,3,19,43 When the latter definition is used, the submandibular space is subdivided into a sublingual space superior to the mylohyoid, a submaxillary space inferior and lateral to the mylohyoid, and a submental space centrally.2,3 Several cadaver dissection studies, some of which have incorporated the injection of colored gelatin, have shown free communication between the submandibular and parapharyngeal spaces.1,19,43 However, other dissection studies78 and clinical and radiologic observations do not support such a communication.69 Cervical fascial ‘‘spaces’’ The cervical fascial ‘‘spaces’’ include the historical ‘‘deep spaces’’ (parapharyngeal, retropharyngeal, danger, prevertebral, and visceral spaces) as well as the more recently defined pharyngeal mucosal and anterior and posterior cervical spaces. Parapharyngeal space. A host of synonyms have been used for this space. It is commonly described as an inverted pyramid, cone, funnel, or triangle with the skull base superiorly and the greater cornu of the hyoid bone or mandible inferiorly,1,2,20,38,78,79 although this concept has been challenged.80 Laterally, it is bordered by the medial pterygoid muscle and parotid gland, posteriorly by the prevertebral muscles or carotid sheath (depending on the definition), and medially by the visceral fascia covering the pharyngeal muscles.1,4,18,78,81 Some authors subdivide the space into the anterior (prestyloid) and posterior (poststyloid) compartments.41,80,82 This subdivision and the communications between this space and adjacent compartments are controversial. Considering the first of these controversies, numerous structures have been suggested to subdivide the parapharyngeal space: the styloid muscles and posterior belly of digastric (the so-called ‘‘styloid dia1062 HEAD & NECK—DOI 10.1002/HED JULY 2014 phragm’’)75,83,84; the tensor veli palatini and its fascia40,84; the ‘‘stylopharyngeal aponeurosis’’18,19,38,78,85; and the levator veli palatini and its fascia.86 To compound the confusion, some authors have added a further subdivision, namely a third medial compartment (retropharyngeal)81,87 or a posterior hypoglossal compartment.88 Some studies have reported free communication between these subdivisions,20,38,47,64 whereas others have found the converse.18,19,37,88 The second controversy centers on whether the parapharyngeal space is entirely enclosed18,78 or communicates with the parotid, submandibular, and/or retropharyngeal spaces.1,20,37,38,47,63,64 Injection of gelatin into the parapharyngeal space of cadavers has shown free communication with the retropharyngeal space1 but no communication in the reverse direction.37 Carotid space. This is bound by the carotid sheath. It is said to be susceptible to infection from any of the surrounding layers and compartments,17,44,47 but clinical studies have found that disease tends to be reasonably isolated along the course of the sheath.2,19 Pharyngeal mucosal space. This term has appeared in the radiologic literature4,89 to describe the space deep to the visceral layer of DCF encircling the pharyngeal constrictor muscles between the skull base and cricoid cartilage; nasopharyngeal, oropharyngeal, and hypopharyngeal divisions are reported.89 The pharyngeal mucosa represents the deepest limit of this space.4,39,50,76,89 The pharyngeal mucosal space is not the same as the ‘‘peritonsillar space,’’ which has been described in surgical texts because this is the potential space between the capsule of the palatine tonsil and the superior constrictor and palatal muscles.2,19,86,90 Nevertheless, the peritonsillar space lies within the pharyngeal mucosal space. Retropharyngeal and danger spaces. Building on earlier studies,11,38,47,54 Grodinsky and Holyoke1 described 2 spaces bounded by visceral fascia anteriorly, prevertebral fascia posteriorly, and the alar fascia in between; these have been reaffirmed in modern studies48 and become known as the retropharyngeal space (anterior) and the danger space (posterior).1 The retropharyngeal space contains lymph nodes, whereas the danger space has no specific contents.48 This division into 2 ‘‘spaces’’ is reinforced in the radiologic literature,4,79,82,91 but some authors either do not describe a ‘‘danger space’’43,45,52,69 or consider the retropharyngeal and danger spaces as a single functional space.4 Craniad to the hyoid, the retropharyngeal space is stated to either communicate freely with the parapharyngeal space1,20,38,47 or be limited by the lateral extent of the pharynx.11,37,39,78 Radiologic studies have reported no communication with the parapharyngeal space in general,82 or with its ‘‘prestyloid’’92 or ‘‘poststyloid’’3 subdivisions. Inferior to the hyoid, the retropharyngeal space is stated to extend anterolaterally around the viscera.1 It has also been suggested that it communicates with the visceral space3,11,19,85 between the level of the thyroid cartilage and inferior thyroid artery.3,79 The inferior limit of the retropharyngeal space is variably described as lying HEAD AND NECK FASCIA AND COMPARTMENTS TABLE 2. Cranial ‘‘spaces’’ and their contents. Previous terms, with subdivisions Parotid space Masticator space, buccomasseteric region Suprazygomatic Infratemporal Nasopharyngeal Retrozygomatic Superficial and deep temporal spaces Buccal space Submandibular space Submaxillary Sublingual Submental Contents Suggested term Parotid gland, retromandibular vein, facial nerve, external carotid artery, lymph nodes Mandible (or just the alveolar ridge), masseter, medial and lateral pterygoid muscles, mandibular division of trigeminal nerve Extension of buccal fat Superficial: superficial temporal vessels and branches of the auriculotemporal and facial nerves, temporoparietal fat pad Buccal fat pad, parotid duct Hypoglossal nerve, lingual nerve, submandibular and sublingual glands, submandibular duct, lymph nodes between the sixth cervical (C6) and fourth thoracic vertebrae (T4),1,3,45 at T1 to T2,2,17,62,93 T3,50 T2 to T6,94 or in the ‘‘upper mediastinum.’’4,95 Prevertebral or perivertebral space. The ‘‘prevertebral space’’ is usually regarded as a potential space between the DLDCF anteriorly and the transverse processes of the vertebrae posteriorly, extending from the skull base to the coccyx.1,2,19,48 An alternative definition is a rectangular space between the MLDCF anteriorly and the DLDCF posteriorly, extending to the mediastinum (ie, the equivalent of the retropharyngeal space described above).11,37,38,85 Others describe a ‘‘perivertebral’’45,52,53 or ‘‘prevertebral’’41,94 space enclosed by fascia extending round to the spinous processes posteriorly; this space has been divided into anterior or ‘‘prevertebral’’ and posterior or ‘‘paraspinal’’ portions by fascial attachments to the transverse processes of the cervical vertebrae.50,95 In these schemes, the prevertebral space is stated to extend down to T3,4 the pericardium,41 or the coccyx.52,95 Anterior and posterior cervical spaces. The radiologic literature refers to ‘‘spaces’’ in the regions occupied by the anterior and posterior triangles of the neck.8,96,97 A ‘‘posterior cervical space’’ is described between the DLDCF covering the scalene muscles and the sternocleidomastoid–trapezius fascia; it is limited anteromedially by the carotid sheath. The posterior cervical space theoretically communicates with the axilla but spread of infection between these sites is uncommon.1 Anterior to the sternocleidomastoid is a separate smaller fat-filled ‘‘anterior cervical space,’’ lying between the superficial and middle layers of DCF, and extending from the hyoid bone to the clavicles.93,97 Parker et al97 described a communication between this space and the submandibular space, despite the presence of a firm fascial attachment of the SLDCF to the hyoid.2,19 Infections in the anterior and posterior cervical spaces tend to be localized or track toward the skin46,93 and therefore are Parotid compartment Masticator compartment Submandibular compartment not usually considered in the clinical literature on deep neck infections.2,20 The real clinical utility of these spaces relates to lymphadenopathy and the staging of metastatic disease, but, for this purpose, lymph nodes are best divided into levels defined by anatomic rather than fascial relations.3,98–100 Visceral space. Much of the confusion about this ‘‘space’’ stems from the variable nomenclature applied to the MLDCF (see above). Thus, the visceral space has been described as a potential space between the trachea, esophagus, and thyroid, and their surrounding visceral fascia1 or, alternatively, is seen as part of a larger space that includes the carotid sheath.47,85 Some authors have divided the visceral space into anterior and posterior components,2,19 but there is no convincing anatomic evidence to support this. The space is reported to extend caudally as far as the tracheal bifurcation and/or arch of the aorta.1,2,11,19,47 The radiologic literature more simply refers to a ‘‘visceral space’’ containing the larynx/trachea, pharynx/esophagus, and thyroid and parathyroid glands, enclosed within the MLDCF.41,52,53,94,95 The American Head and Neck Society describes this space as extending back to the alar fascia100 and there is confusion about whether it communicates directly with the retropharyngeal space. Recommendations on compartments The concept of ‘‘spaces’’ assists with differential diagnosis, understanding the spread of disease, and clinical management, including surgical access. However, the term ‘‘compartment’’ is more appropriate than ‘‘space’’ as no part of the head or neck is ‘‘free, available, or unoccupied.’’60 Compartments may be bounded by bone and/or muscle, as well as fascia, and individual compartments may intercommunicate. The trend to subdivide these compartments into smaller and smaller regions should be resisted because this becomes progressively less meaningful to clinical practice. The following compartments, summarized in Tables 2 and 3, are suggested. HEAD & NECK—DOI 10.1002/HED JULY 2014 1063 GUIDERA ET AL. TABLE 3. Cervical compartments and their contents. Previous terms, with subdivisions Parapharyngeal space, paranasopharyngeal, lateral pharyngeal, peripharyngeal, pharyngomaxillary, pterygopharyngomaxillary, pterygopharygneal, pterygomandibular, pharyngomasticatory, and lateral pharyngeal cleft Prestyloid/anterior/anterolateral Poststyloid/retrostyloid/posterior/posteromedial Carotid space, carotid sheath, vascular space Retropharyngeal space Danger space Perivertebral space, paravertebral space, perivertebral space Prevertebral space Paravertebral, perivertebral, paraspinal Visceral space, pretracheal space, anterior visceral space, previsceral space Anterior cervical space Posterior cervical space Contents Suggested term Fat, tonsillar vessels, ascending palatine artery ICA, IJV, cranial nerves IX, X, XI and XII, sympathetic plexus, and lymph nodes Parapharyngeal compartment ICA, IJV, cranial nerve X, sympathetic plexus, and lymph nodes Fat, lymph nodes (suprahyoid only) No contents Prevertebral muscles Paraspinal muscles, phrenic nerve, and cervical nerve roots Pharynx, larynx, trachea, esophagus, thyroid gland (1/2 parathyroid glands) Lymph nodes Lymph nodes, cranial nerve XI, and cervical plexus Carotid compartment Retropharyngeal compartment Prevertebral compartment Perivertebral compartment Visceral compartment Levels 1 to 6 Abbreviations: ICA, internal carotid artery; IJV, internal jugular vein; IX, glossopharyngeal nerve; X, vagus nerve; XI, spinal accessory nerve; XII, hypoglossal nerve. Parotid compartment. There is clear benefit in defining this compartment for radiologic assessment. Surgery tends to center around facial nerve preservation but fascial arrangements are useful in analyzing disease spread, particularly in relation to the deep lobe of the parotid and the parapharyngeal space. Masticator compartment. This compartment is bound by the masticator fascia. There is no clear clinical benefit from subdividing the compartment into temporal, infratemporal, or retrozygomatic portions, as these are continuous and inconsistently applied. The term ‘‘infratemporal fossa’’ is best avoided when describing fascial compartments. Although the buccal region houses a subdivision of the masticator compartment bordered laterally by subcutaneous tissue, medially by visceral fascia covering buccinator, and posteriorly by masticator fascia covering the masseter muscle, there is no obvious advantage from labeling this as a separate ‘‘buccal compartment’’ because it is in continuity with the masticator compartment and can be localized clinically by reference to the buccal fat pad. Submandibular compartment. This comprises the potential ‘‘space’’ craniad and caudad to the mylohyoid muscle bound inferolaterally by the fascia of the submandibular compartment as it passes between the mandible and hyoid. There is no discrete sublingual space. We recommend that this potential space is known as the submandibular compartment, with ‘‘floor of mouth’’ (as advised by the American Joint Committee on Cancer)99 being used to describe the ‘‘sublingual region’’ craniad to the mylohyoid. Parapharyngeal and carotid compartments. In the suprahyoid region of the neck, there are distinct carotid and 1064 HEAD & NECK—DOI 10.1002/HED JULY 2014 parapharyngeal compartments. The terms ‘‘prestyloid’’ and ‘‘poststyloid,’’ although useful for traditional surgical approaches to the parapharyngeal compartment, are not anatomically accurate and should be abandoned. The current literature does not permit reliable conclusions about the fascial arrangements and connections related to the parapharyngeal compartment; in particular, the relationship between the styloid muscles and the pharyngotympanic tube within the compartment is poorly defined. Retropharyngeal compartment. Contemporary crosssectional imaging cannot reliably distinguish the fascial layer between the retropharyngeal space and the danger space. Clinically, treatment decisions on infections in this region are based on physical findings and response to antibiotics rather than whether the infection is in one ‘‘space’’ or the other. Therefore, it is more useful to consider a single retropharyngeal compartment. Further investigations are needed to define the lateral and inferior limits of this compartment. Prevertebral and perivertebral compartments. The former is situated anterior to the cervical vertebral bodies and transverse processes and bound anteriorly by prevertebral fascia. The latter is located posterior to the transverse processes of the cervical vertebrae and enclosed by perivertebral fascia. Visceral compartment. The precise fascial arrangement of this compartment is not well understood and may vary between individuals. Broadening the definition of the visceral compartment to the region encompassed by the visceral fascia seems appropriate. Whether it is in continuity HEAD AND NECK FASCIA AND COMPARTMENTS FIGURE 1. (A–D) The layers of cervical fascia. (A) Subcutaneous tissue. (B) Masticator fascia, submandibular fascia, and sternocleidomastoidtrapezius fascia. The fascia covering the lateral surface of the parotid gland is controversial and therefore not shown. (C) Strap muscle fascia (green) and perivertebral fascia (purple). (D) Visceral fascia (orange) and carotid sheath. with the retropharyngeal space at any site is unclear. Functionally, the visceral compartment is concerned with the airway, deglutition, and endocrine functions. The terms ‘‘pretracheal,’’ ‘‘previsceral,’’ and ‘‘anterior visceral’’ should no longer be used. Adopting this scheme would allow consideration of a ‘‘strap muscle compartment’’ and a ‘‘sternocleidomastoidtrapezius compartment’’ because these are functional units bound by fascia. However, recognition of these compartments has limited clinical utility. The ‘‘pharyngeal mucosal space’’ and ‘‘anterior and posterior cervical spaces’’ are not precise anatomic compartments and these terms are not currently used by surgeons. They have been introduced in the last few decades for radiologic diagnosis. Pathology within the ‘‘pharyngeal mucosal space’’ is actually within the pharyngeal submucosa. When describing lymph nodes during the staging of malignant disease, levels I to VI as contained described by the Union for International Cancer Control staging system99,100 are appropriate descriptors. CONCLUSIONS This review of anatomic and radiologic literature demonstrates the confusion that exists about fascial layers and ‘‘spaces’’ in the head and neck. Controversy surrounds the nomenclature, boundaries, and communications and further research is required to clarify the anatomy of some regions. HEAD & NECK—DOI 10.1002/HED JULY 2014 1065 GUIDERA ET AL. FIGURE 2. (A and B) Fascial layers of the head and face with associated compartments. (A) Oblique-coronal section with comparable CT scan demonstrating the cranial fascia (left) and compartments (right). (B) Comparable axial MRI at the level of the hard palate. Naming fascial layers in functional terms and removing confusing descriptors such as ‘‘superficial layer of deep’’ creates a less ambiguous classification. Thus, the ‘‘superficial cervical fascia’’ should be referred to as ‘‘subcutaneous tissue’’ and the layers of the ‘‘deep cervical fascia’’ are better named according to their function and gross anatomy (Table 1) (Figures 1-3). The term ‘‘space’’ should be avoided in preference to the more accurate term ‘‘compartment.’’ Although some of the compartments in our scheme are identical to standard descriptions, others are different and offer a more rational approach to classification. The ‘‘submandibular compartment’’ is a midline region bound superiorly by the tongue and oral mucosa and inferiorly by the submandibular fascia; the mylohyoid lies within the compartment but does not provide a functional subdivision. The ‘‘strap muscle compartment’’ and its fascia is distinct from the ‘‘visceral compartment.’’ The ‘‘carotid compartment’’ traverses the whole neck and lies posterolateral to the styloid and its associated muscles in the suprahyoid region; it should not be considered part of the ‘‘parapharyngeal compartment,’’ which is a discrete region with different contents. The ‘‘retropharyngeal compartment’’ is divided by the alar fascia, but because this cannot be reliably visualized by current imaging, it is best to consider this as a single compartment, rendering the term ‘‘danger space’’ obsolete. By clearly defining fascial layers and their associated compartments, the relationships between different regions of the neck become better understood and anatomic and radiologic interpretations more congruent. Our proposal for a common language underpinned by 1066 HEAD & NECK—DOI 10.1002/HED JULY 2014 evidence-based anatomic findings should enhance understanding of the neck and facilitate clearer interdisciplinary communication. FIGURE 3. A. Cervical fascial layers and associated compartments. B. Comparable axial MRI at the level of the thyroid isthmus. HEAD Acknowledgment We thank Robbie McPhee, Medical Illustrator/Graphic Artist, Department of Anatomy, University of Otago, for assistance with the images. REFERENCES 1. Grodinsky M, Holyoke EA. The fasciae and fascial spaces of the head, neck and adjacent regions. Am J Anat 1938;63:367–408. 2. Levitt GW. Cervical fascia and deep neck infections. Otolaryngol Clin North Am 1976;9:703–716. 3. Som PM, Curtin HD. Head and neck imaging. 5th ed. American Journal of Roentgenology. St Louis, MO: Elsevier Mosby; 2011. p 3080. 4. Harnsberger HR. CT and MRI of masses of the deep face. Curr Probl Diagn Radiol 1987;16:141–173. 5. 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