Approach to Masses in Head and Neck Spaces

Abstract

The neck is anatomically complex and exhibits a wide range of pathologies, making the imaging diagnosis of masses in this region challenging. Organizing the neck into specific “spaces” based on fascial planes and individual contents is a helpful approach to generating a differential diagnosis. Once a mass is localized within a neck space, then specific imaging features and clinical context can be applied to narrow these different considerations. In this chapter, we will review the normal anatomy and contents of each space in the suprahyoid and infrahyoid neck and discuss the specific pathologies typically found in each space.

FormalPara Learning Objectives

• To understand how the layers of the deep cervical fascia, along with muscles and bones, help define “spaces” or compartments in the neck.

• To understand the normal anatomy and contents of each of the spaces in the suprahyoid and infrahyoid neck.

• To accurately localize neck pathology into a specific space in order to generate the most appropriate differential diagnosis.

1 Introduction to Head and Neck Spaces

While the neck is anatomically complex, it can be organized into specific “spaces” or compartments based on fascial planes and individual contents [1, 2]. Some authors argue that the term “space” may be an oversimplification and lead to confusion. These authors propose naming fascial layers in functional terms and using the term “compartment,” which can be bound by bone, muscle, and/or fascia. For consistency with radiologic literature, this review will use the term “space” but will attempt to point out any potentially confusing terms and propose newer terminology to promote interdisciplinary communication. The ability to place pathology within a neck space is the first step to generating a differential diagnosis; then, specific imaging features and clinical context can be applied to narrow these different considerations.

The neck can be divided into suprahyoid and infrahyoid spaces by the hyoid bone. Some head and neck spaces traverse both the suprahyoid and infrahyoid neck. Two layers of fascia, superficial and deep, are commonly used to define the spaces of the neck. The superficial cervical fascia (SCF) is a thin layer, investing loose connective and adipose tissue, the platysma muscle, superficial lymph nodes, and muscles of facial expression. Some surgeons refer to SCF simply as “subcutaneous tissue” [3] to prevent confusion with the superficial layer of the deep cervical fascia (SLDCF), which is described below.

The deep cervical fascia is further subdivided into three layers: superficial, middle, and deep. The superficial layer of deep cervical fascia (SLDCF) lies between the SCF (or subcutaneous tissue) and the muscles of the neck; it attaches anteriorly to the hyoid, superiorly to the mandible, and to the mastoid process and external occipital protuberance. The “rule of twos” is a helpful way to remember that the SLDCF encloses two glands (submandibular and parotid) and two muscles (sternocleidomastoid and trapezius). Some surgeons refer to the subdivisions of the SLDCF as the masticator fascia, submandibular fascia, and sternocleidomastoid/trapezius fascia, choosing to define fascia by function.

The middle layer of deep cervical fascia (MLDCF) extends from the skull base to the mediastinum and is divided into a muscular layer and a visceral layer. The muscular layer invests the strap muscles, while the visceral layer (also called buccopharyngeal in the suprahyoid neck) invests the larynx, pharynx, trachea, esophagus, and thyroid. The deep layer of deep cervical fascia (DLDCF) surrounds the vertebral column and paravertebral muscles with two distinct components: the alar and prevertebral fascia. The alar layer forms the posterior and lateral walls of the retropharyngeal space and bridges the transverse processes of the vertebrae. The prevertebral layer encloses the paraspinal muscles: the longus colli and longus capitis muscles; the anterior, middle, and posterior scalene muscles; and the levator scapulae. The carotid sheath is generally thought to be composed of all three layers of DCF though the thickness of the carotid sheath varies among individuals and at different levels in the neck.

The suprahyoid neck spaces comprise the area from the base of skull to the hyoid bone, excluding the orbits, paranasal sinuses, and oral cavity. The spaces of the suprahyoid neck include the pharyngeal mucosal space (PMS), the sublingual space (SLS), the submandibular space (SMS), the parapharyngeal space (PPS), the parotid space (PS), and the masticator space (MS). Those spaces traversing the entire neck (suprahyoid and infrahyoid) include the carotid space (CS), the retropharyngeal and danger space (RPS), and the perivertebral space (PVS). In addition to the entire neck spaces (listed above), the infrahyoid neck also contains the visceral space (VS), which includes the thyroid and parathyroid glands and the larynx, hypopharynx, trachea, and cervical esophagus.

2 Suprahyoid Neck: Pharyngeal Mucosal Space (PMS)

2.1 Anatomy and Contents

The contents of the pharyngeal mucosal space include the mucosa of the nasopharynx and oropharynx, as well as submucosal structures such as Waldeyer’s ring, minor salivary glands (MSGs), the pharyngeal constrictor and levator veli palatine muscles, and the torus tubarius bordering the Eustachian tube orifice [4]. Waldeyer’s ring comprises the adenoids and the palatine and lingual tonsils; the ring-like configuration of lymphoid tissue can be thought of as a mechanism to protect the body from inhaled and ingested antigens. Deep mucosa-lined tonsillar crypts result in a characteristic striped appearance on contrast-enhanced imaging and may hide small primary tumors.

Key Point

• While squamous cell carcinoma is the most common tumor of the PMS, the presence of Waldeyer’s ring lymphoid tissue and submucosal minor salivary glands may result in lymphoproliferative and salivary neoplasms, respectively.

2.2 Pathology

The most common malignant neoplasm in this space is squamous cell carcinoma arising from the mucosa, which is covered in a separate chapter. Tumors arising from Waldeyer’s ring lymphoid tissue and MSGs are considerably less common. Inflammatory disease of the oropharynx represents a spectrum ranging from non-focal tonsillitis to tonsillar or peritonsillar abscess (Fig. 16.1). Congenital lesions of the PMS include the central nasopharyngeal Tornwaldt cyst and those related to the embryologic thyroglossal duct, including cysts and the lingual thyroid (Fig. 16.2).

Fig. 16.1

Axial CECT shows a discrete rim-enhancing fluid collection (arrow) lateral to an enlarged and inflamed tonsil in a patient with tonsillitis and peritonsillar abscess

Fig. 16.2

Sagittal CECT shows two sites of ectopic lingual thyroid tissue, one in the pharyngeal mucosal space at the base of tongue and the other anterior to the hyoid bone. Additional images confirmed absence of normal thyroid tissue in the thyroid bed

3 Suprahyoid Neck: Parapharyngeal Space (PPS)

3.1 Anatomy and Contents

The PPS is a triangular fat-containing space lateral to the PMS. It is bound laterally by the masticator and parotid spaces, posteriorly by the retropharyngeal and carotid spaces, and superiorly by the skull base, with inferior extension into the submandibular space. The PPS contents are simple: fat, minor salivary glands, and, rarely, lymph nodes.

3.2 Pathology

Primary pathology of the PPS is rare, with the majority of lesions originating from minor salivary glands and representing benign mixed tumors (BMTs) [5]. The PPS is most often affected by pathology of neighboring spaces, and the pattern of deviation or deformity of the PPS fat may be helpful in identifying the space of origin. For example, while a well-defined markedly T2-hyperintense mass bounded entirely by fat is likely a primary PPS BMT, a similar lesion contiguous with the deep lobe of the parotid and displacing the PPS fat anteromedially more likely originates in the parotid space (Fig. 16.3). Similarly, masticator space lesions displace the PPS fat posteromedially, PMS lesions laterally, and carotid space lesions anteriorly.

Fig. 16.3

(a) Primary BMT of the left PPS (arrow) is surrounded entirely by fat on axial T1-weighted image. (b) Axial T1-weighted image shows a primary BMT of the left parotid space (arrow) inseparable from the deep lobe and displacing PPS fat medially

4 Suprahyoid Neck: Masticator Space (MS)

4.1 Anatomy and Contents

Located lateral to the PPS, the MS contains the muscles of mastication (masseter, temporalis, and medial and lateral pterygoids), the posterior body and ramus of the mandible, and the mandibular nerve (a branch of the trigeminal nerve).

4.2 Pathology

As with the PPS, most pathology of the MS originates in the neighboring spaces, the most common being odontogenic infection arising from molar teeth within the neighboring oral cavity [6]. Dental abscesses may extend to the medial pterygoid or masseter muscles and may also result in osteomyelitis of the posterior mandibular body and condyle (Fig. 16.4). Another common non-neoplastic lesion affecting the MS is the venous malformation (VM), which has a predilection for the muscles of mastication and is a frequent incidental finding on imaging studies performed for unrelated indications (Fig. 16.5). The presence of phleboliths within a markedly T2-hyperintense and heterogeneously enhancing mass is virtually pathognomonic for VM. Neoplastic entities of the MS include perineural spread of tumor to cranial nerve V3 or, much less commonly, primary nerve sheath tumors of cranial nerve V3 such as schwannomas. Primary neoplasms of the muscles of mastication, such as sarcomas and lymphoproliferative malignancies, are exceedingly rare. More often, malignant MS disease results from spread of tumors arising in the pharynx, oral cavity, or parotid space.

Fig. 16.4

Axial CECT image shows a fluid and gas collection centered in the right medial pterygoid muscle (arrow), representing odontogenic abscess arising from the right mandibular third molar

Fig. 16.5

Axial T2-weighted image shows a markedly hyperintense mass in the left masseter muscle with fluid-fluid level and internal rounded areas of signal void (arrow). These represent phleboliths, which are virtually pathognomonic for a venous malformation

5 Suprahyoid Neck: Parotid Space (PS)

5.1 Anatomy and Contents

The PS contains the parotid gland, facial nerve, retromandibular vein, and branches of the external carotid artery. The plane of the facial nerve bisects the parotid gland into superficial and deep lobes; localization of lesions into one of these lobes is key to prevent inadvertent facial nerve injury during resection. The plane may be approximated on cross-sectional imaging by identifying the stylomandibular tunnel, located between the styloid process and the posterior cortex of the mandibular condyle, as well as by the position of the retromandibular vein.

5.2 Pathology

The parotid gland is the only salivary gland to contain lymph nodes, with the important consequence that the differential diagnosis for lymphadenopathy, including neoplastic and inflammatory etiologies, must be considered for any PS mass [7]. The parotid lymph nodes also represent first echelon drainage for cancers of the external auditory canal as well skin cancers of portions of the scalp and facial skin. Fortunately, most primary salivary epithelial neoplasms represent benign mixed tumors; these typically demonstrate very high signal on T2-weighted and ADC scans (Fig. 16.6). This is one of the few parotid neoplasms that demonstrates characteristic imaging features. In general, given the very diverse neoplastic histology of this region, a specific diagnosis cannot be reliably predicted based on CT or MR imaging. Infectious/inflammatory diagnoses in the PS include both acute and chronic parotitis. Acute parotitis may occur secondary to obstruction by calculi, retrograde migration of oral flora due to poor salivary flow, or hematogenic viral infection. Chronic parotitis is typically bilateral and reflects underlying systemic disease such as Sjogren syndrome or sarcoidosis.

Fig. 16.6

(a) Axial STIR image demonstrates a well-circumscribed markedly T2 hyperintense mass in the superficial lobe of the right parotid, a pathologically proven benign mixed tumor (arrow). (b) The corresponding ADC map demonstrates high signal, indicating relatively free diffusivity of water in these gelatinous tumors

Key Point

• The parotid gland is the only salivary gland to contain lymph nodes; the differential diagnosis for lymphadenopathy must be considered for any PS mass.

6 Suprahyoid Neck: Sublingual (SLS) and Submandibular Space (SMS)

6.1 Anatomy and Contents

The oral cavity (OC) is anatomically complex with an extensive, convoluted mucosal surface covering its constituent structures: the tongue, floor of mouth, hard palate, cheeks, and gingiva. The SLS is the portion of the floor of mouth below the tongue and above the mylohyoid muscle, a sling-like structure that separates the OC above from the SMS below (Fig. 16.7) [8]. The SLS contains the sublingual glands (SLGs), the deep lobes of the submandibular glands (SMGs) and submandibular ducts, the “neurovascular bundles” (lingual nerves, arteries, and veins), and cranial nerves 9 and 12. The SMS is relatively simple in composition, containing only the SMG superficial lobe, fat, lymph nodes, and the facial artery and vein.

Fig. 16.7

Coronal T2-weighted image shows the mylohyoid (arrow), the sling-like muscle that separates the oral cavity above from the SMS below

6.2 Pathology

Much like in the MS, inflammatory disease is a common entity in the SLS and SMS, with the teeth and salivary glands as the principal sources. It is important to recognize that symptoms localized to the SMS could be caused by pathology in the SLS. For example, sialoliths frequently impact distally at the punctum of the submandibular duct, which is part of the SLS. An obstructing sialolith in the SLS may cause upstream inflammatory disease of the SMG, part of which is located in the SMS. Dental artifact frequently obscures calculi at the anterior floor of mouth, making a high index of suspicion and careful search imperative to diagnosis (Fig. 16.8). Obstruction of the SLG or a submucosal MSG duct may result in formation of a ranula, an epithelial-lined cyst within the SLS. When these rupture, they may form pseudocysts that may “dive” or “plunge” behind the posterior free edge of the mylohyoid muscle into the SMS (Fig. 16.9). The vast majority of neoplasms in this region are squamous cell carcinomas originating from the OC mucosa. Salivary epithelial tumors may arise from the major salivary glands (SLG, SMG) or from minor salivary glands (MSGs) lying within the SLS submucosal space.

Fig. 16.8

(a) Axial CECT depicts an enlarged, edematous SMG (arrow) in the SMS, representing acute sialadenitis. (b) Axial CECT identifies the causative obstructing calculus (arrow), located in the submandibular duct at anterior floor of mouth in the SLS

Fig. 16.9

Axial CECT depicts a “diving” or “plunging” ranula (arrow) extending from the SLS to the SMS behind the posterior free edge of the mylohyoid muscle

7 Infrahyoid Neck: Visceral Space (VS)

7.1 Anatomy and Contents

The VS is a central tubular space extending from the hyoid to the mediastinum. Enclosed by the middle layer of deep cervical fascia, the VS is the only space confined entirely to the infrahyoid neck. Its contents include: the thyroid and parathyroid glands, the recurrent laryngeal nerve, the larynx, hypopharynx, trachea, and cervical esophagus. The thyroid gland is located anterior to the prevertebral musculature and posterior to the infrahyoid strap musculature, in close proximity to other vital structures of the VS such as the larynx, trachea, and esophagus. The tracheoesophageal groove lies posteromedial to the thyroid lobe and contains several important structures including the recurrent laryngeal nerve, paratracheal nodes, and parathyroid glands.

7.2 Thyroid and Parathyroid Pathology

Abnormalities of the thyroid gland are a major indication for imaging the VS. In general, ultrasound is the workhorse imaging modality for inflammatory (i.e., Hashimoto’s) or infectious thyroiditis and for evaluation of the intrathyroidal nodule. Intrathyroidal nodules may represent colloid cysts, adenomas, differentiated thyroid cancer, or rarely, metastases. Many ultrasound classification systems exist to risk stratify these nodules and determine whether biopsy is indicated, including ones by the American Thyroid Association (ATA) and the Society of Radiologists in Ultrasound (SRU). Newer systems such as European Thyroid Imaging and Reporting Data System (EU-TIRADS) and the American College of Radiology Thyroid Imaging and Reporting Data System (ACR TIRADS) are gaining acceptance for their point-based approach [9, 10], particularly ACR TIRADS, with emerging studies demonstrating its high diagnostic performance and reduction of unnecessary biopsies [11, 12].

Thyroid cancer is a heterogeneous group of malignancies, including differentiated thyroid carcinomas (papillary and follicular), medullary and anaplastic carcinomas, and non-Hodgkin lymphoma. Cross-sectional imaging is most appropriate when there is a concern for extrathyroidal extension of tumor [13, 14] into surrounding structures such as the trachea or esophagus (Fig. 16.10). For rapidly enlarging thyroid masses, both anaplastic carcinoma and lymphoma should be considered. For multinodular goiters (MNG), ultrasound is used for surveillance of individual nodules, but non-contrast CT (NCCT) is often the choice for presurgical evaluation if airway compression necessitates removal. NCCT is helpful to evaluate the extent of airway compression and substernal extension for surgical planning and to exclude overt signs of malignancy. Local extension into trachea, tracheoesophageal (TE) groove, or infrahyoid strap muscles, vocal cord paralysis from involvement of the recurrent laryngeal nerve in TE groove, and pathologic cervical adenopathy are imaging findings that suggest thyroid malignancy.

Fig. 16.10

Post-contrast axial T1-weighted image with fat saturation demonstrates a papillary thyroid cancer with extra-thyroidal extension and invasion of the trachea and esophagus (arrow)

Key Point

• US is the primary imaging modality for both inflammatory disease and work-up of thyroid nodules, with cross-sectional imaging used when there is concern for extrathyroidal extension of tumor, or to evaluate potential airway compression or substernal extension of goiter.

Congenital lesions in the VS include infrahyoid thyroglossal duct cysts or ectopic thyroid tissue along the course of the thyroglossal duct. Thyroglossal duct cysts are the most common congenital neck masses (Fig. 16.11); most present before age 10 as a painless, movable mass that may fluctuate in size after upper respiratory tract infection. When suprahyoid they are characteristically midline while infrahyoid lesions are often paramidline. Nodules in the tracheoesophageal groove may represent parathyroid adenomas (or rare carcinomas), lymph nodes, or unusual schwannomas of the recurrent laryngeal nerve. Parathyroid adenomas are characteristically hypervascular, demonstrating rapid wash-in on early arterial phase and relatively rapid wash-out on venous phase multiphase contrast-enhanced CT [15].

Fig. 16.11

Axial CECT demonstrates a paramidline infrahyoid cystic lesion (arrow) consistent with thyroglossal duct cyst

7.3 Larynx, Hypopharynx, Trachea, and Esophagus Pathology

The most common indication for imaging of larynx and hypopharynx is staging of squamous cell carcinoma (a primary mucosal space abnormality), which will be discussed in a separate chapter. Much less common, submucosal tumors are usually well circumscribed on imaging and will not have an overlying mucosal abnormality on endoscopy. The differential diagnosis for submucosal masses includes minor salivary gland tumors, sarcomas such as laryngeal chondrosarcoma, and lymphoma. Benign lesions of the larynx, including papillomas and hemangiomas, are also uncommon. Laryngoceles, also called saccular cysts, are seen as dilated laryngeal ventricular saccules extending cranially within the paraglottic fat (Fig. 16.12). These are almost always unilateral and may be confined to the paralaryngeal space (“internal”) or may extend laterally into the cervical soft tissues through the thyrohyoid membrane (“external”). Laryngoceles that contain both an internal and external component are classified as mixed type. While this benign entity is usually functional and related to chronic increased glottic pressure, a small number (5–20%) may herald obstructing squamous cell carcinoma [16].

Fig. 16.12

Coronal CECT demonstrates a dilated, fluid-filled left ventricular saccule, consistent with laryngocele. There is lateral extension through the thyrohyoid membrane indicative of an external component (white arrow). A normal right laryngeal ventricle is seen (yellow arrow)

In the inflammatory category, epiglottitis should be suspected in a child with difficulty breathing and swallowing and may initially be evaluated with plain film. When there is a classic “thumb” sign reflecting the swollen epiglottis, treatment may be initiated and CECT may not even be required. Adults may have supraglottitis with CECT showing thickened, edematous epiglottis and aryepiglottic folds.

8 Entire Neck: Carotid Space (CS)

8.1 Anatomy and Contents

The carotid space spans the suprahyoid and infrahyoid neck, extending from the skull base to the aortic arch, with all three layers of the deep cervical fascia contributing to the carotid sheath [17]. It is located posterior to the styloid process (and is therefore termed the post-styloid PPS by some authors), anterior to the prevertebral muscles, and lateral to the retropharyngeal space. The CS can be further subdivided into nasopharyngeal, oropharyngeal, cervical and mediastinal components. The suprahyoid CS contains the carotid artery, internal jugular vein (IJV), cranial nerves 9–12, and the sympathetic chain. The infrahyoid CS differs in that all cranial nerves have exited except the vagus nerve. Lymph nodes are closely associated with the carotid space, along its lateral border. The carotid artery is located medially, IJV laterally, vagus nerve posteriorly along the vessels, and the sympathetic chain posteriorly within the sheath.

Key Point

• The CS spans the suprahyoid and infrahyoid neck, with all three layers of the DCF contributing to the carotid sheath.

8.2 Pathology

Masses in the suprahyoid CS classically displace the parapharyngeal fat anteriorly and splay the carotid and jugular vein, often displacing the ICA anteriorly and IJV posterolaterally. Vascular pathology, primarily dissection or pseudoaneurysm of the carotid artery or thrombosis/thrombophlebitis of the IJV, may easily be overlooked on routine neck CT or MRI. Special attention should be paid to the CS to exclude dissection in any patient presenting with Horner’s syndrome. An IJV thrombophlebitis caused by extension of oropharyngeal or odontogenic infection is referred to as Lemierre syndrome (Fig. 16.13). CT and MR angiography or venography are studies of choice if there is high clinical suspicion for a vascular lesion.

Fig. 16.13

(a) Axial CECT demonstrates a filling defect in the right IJV (arrow), consistent with thrombophlebitis. (b) In close proximity to the IJV thrombus, axial CECT identifies a right peritonsillar abscess in the PMS (arrows). The combination of these findings is consistent with Lemierre syndrome

The most common masses in the high nasopharyngeal CS often dumbbell inferiorly from the jugular foramen and include glomus jugular paraganglioma, schwannoma, and meningioma. Close attention to the skull base is important in any patient presenting with hoarseness/vocal cord palsy or other cranial neuropathy involving CNs 9–12. Bony changes on CT are an important clue to the correct diagnosis of a jugular foramen/CS mass at the skull base. Permeative destruction favors paraganglioma, smooth remodeling is characteristic of schwannoma, and hyperostosis suggests a CS mass is a meningioma. On MRI, paragangliomas are intensely enhancing and can have the classic “salt and pepper” appearance with the “salt” representing microhemorrhages on T1-weighted (T1W) images and the “pepper” representing flow voids on T2-weighted (T2W) images. Carotid body and glomus vagale paragangliomas are also found in the CS. Carotid body tumors are located at the carotid bifurcation in the infrahyoid neck and splay the internal and external carotid arteries (Fig. 16.14). CS nerve sheath tumors include schwannomas and neurofibromas. Schwannomas are typically fusiform enhancing tumors, sometimes with cystic change, whereas neurofibromas are classically hypodense and hypoenhancing on CT and have a characteristic target sign on MRI.

Fig. 16.14

(a) Axial CECT demonstrates an avidly enhancing mass (arrow) at the right carotid bifurcation splaying the internal and external carotid arteries. (b) Axial T2w with fat saturation image demonstrates characteristic flow voids (the “pepper” of the “salt and pepper” appearance) within the mass (arrow). These findings are consistent with carotid body paraganglioma

9 Entire Neck: Retropharyngeal, Danger, and Prevertebral Spaces (RPS)

9.1 Anatomy and Contents

As mentioned in the introduction, the DLDCF has two components, the alar and prevertebral fascia. This results in the formation of three posterior neck spaces: (1) retropharyngeal space (RPS), between the visceral and alar fascia, (2) danger space, between the alar and prevertebral fascia, and (3) prevertebral space, between the prevertebral fascia and the vertebral periosteum (part of the perivertebral space, discussed below). The importance of recognizing the division into these spaces primarily relates to their inferior extent. While the RPS terminates at the level of the T3 vertebra, the danger space extends more inferiorly to a point just above the diaphragm, and the prevertebral space continues to the coccyx. Though we typically cannot distinguish these spaces on imaging, we must remember to follow a posterior neck space collection to its inferior extent and be cognizant of the fact that this may lie within the chest or below. Contents of the suprahyoid RPS are simple: fat and lymph nodes. The RPS in the infrahyoid neck is a potential space, collapsed in the normal setting.

Key Point

• Retropharyngeal collections that have entered the danger or prevertebral spaces can descend to the mediastinum and as far inferiorly as the coccyx.

9.2 Pathology

Disease processes in the RPS can be categorized as related to the presence of fluid and/or nodal pathology. Fluid within the RPS may be encapsulated and represent an abscess or, much less commonly, a pseudomeningocele as a complication of spinal surgery. More frequent is unencapsulated edema or effusion of the RPS, and this may occur as a reaction to a wide variety of disease processes such as pharyngitis, lymphatic or venous obstruction, angioedema (Fig. 16.15), or radiation therapy [18]. Cervical osteomyelitis/discitis can secondarily result in fluid in the RPS. Nodal enlargement may occur in the setting of inflammatory or neoplastic processes. When there is pharyngitis, lymphadenopathy may be reactive and homogenous, or, particularly in children, an intranodal abscess may develop and rupture into the RPS. RPS lymph nodes may be involved in hematologic malignancy, such as lymphoma, or may represent sites of metastatic disease from local malignancies, particularly those of the pharynx, paranasal sinuses, and thyroid gland.

Fig. 16.15

Sagittal CECT demonstrating unencapsulated fluid in the retropharyngeal space in a patient presenting with angioedema

10 Entire Neck: Perivertebral Space (PVS)

10.1 Anatomy and Contents

The perivertebral space (PVS) is a cylindrical space around the vertebral column, invested in the DLDCF from the skull base to the mediastinum. The PVS can be subdivided into the prevertebral space and the paraspinal space [19]. The contents of the PVS include the vertebral bodies, disc spaces, musculature, and the vertebral arteries in the foramen transversarium. The RPS lies directly anterior to the PVS, and the paired carotid spaces lie anterolateral. The prevertebral muscles are invested in the anterior DLDCF, known as the “carpet” by surgeons. It is tenacious and serves as a barrier to infection and neoplasm. Lesions in the PVS tend to lift or displace the prevertebral muscles anteriorly, whereas RPS lesions displace these muscles posteriorly.

10.2 Pathology

The vast majority of pathologic lesions in the perivertebral space involve the vertebral bodies and disc spaces, and the minority of lesions are centered in the paraspinal musculature. Therefore, pyogenic discitis/osteomyelitis and bone metastasis are the most common pathologies found in this space. Atypical infections such as tuberculosis are less common but have characteristic imaging features such as sparing of the disc spaces. Primary bone tumors are also uncommon but have characteristic locations and appearance. For example, chordomas can be suggested when a lesion is found in the upper cervical spine with characteristic bright T2 signal and enhancement. An important differential diagnosis to consider in a patient with acute onset neck pain and dysphagia is calcific tendinitis of the longus colli muscle (Fig. 16.16), also referred to as prevertebral calcific tendinitis. Imaging features include prevertebral edema and calcification anterior to C2.

Fig. 16.16

(a) Sagittal CECT soft tissue window demonstrates prevertebral edema (arrow) in a patient with 3 days of acute onset neck pain. (b) Sagittal bone windows show calcification anterior to C2 (arrow), diagnostic of longus colli calcific tendinitis (prevertebral calcific tendinitis)

11 Concluding Remarks

The neck is anatomically complex but can be organized into compartments or “spaces” to help organize the approach to neck masses. A thorough understanding of fascial planes, the various spaces and their normal contents will help the radiologist generate the best differential diagnoses to appropriately guide management. The parapharyngeal space (PPS) fat is especially important in the analysis of most suprahyoid neck masses, as the mass effect on this triangular fat pad often helps to localize the space of origin. Pathology will displace the PPS in a predictable pattern. For example, masses arising in the deep lobe of the parotid tend to displace the PPS anteromedially, carotid space masses displace the PPS anteriorly, masticator space masses push the PPS posteriorly, and pharyngeal mucosal space masses often push the PPS laterally. Each compartment has common and uncommon pathology, typically based on the normal contents. Therefore, once a lesion is localized to the correct space, the radiologist can utilize imaging features and clinical information to provide a tailored list of differential considerations, or in some cases, a specific most likely diagnosis.

H&N Space Contents

Space	Boundaries	Major contents	Common pathology
Pharyngeal mucosal (PMS)	Mucosa to pharyngeal constrictors of nasopharynx and oropharynx (some include hypopharynx and oral cavity)	Mucosa, Waldeyer’s ring, minor salivary glands, constrictor and levator palatine muscles, cartilaginous Eustachian tube	Malignant tumors (mucosal = SCC or NPC and submucosal = minor salivary tumors or lymphoma) Pharyngitis, tonsillitis
Parapharyngeal (PPS)	Skull base to mandibular angle, borders PPS, CS, PS, MS	Fat, minor salivary glands	Benign salivary tumors, rare branchial cleft cyst or vascular malformation
Masticator (MS)	Skull base to mandibular angle, lateral to PPS	Muscles of mastication, posterior body and ramus of mandible, CNV3	Odontogenic infections, venous malformations, sarcomas
Parotid (PS)	Enclosed within the parotid fascia, lateral to PPS, MS	Parotid gland, CN7, lymph nodes, retromandibular vein, external carotid artery branches	Pleomorphic adenoma Low and high grade malignant salivary neoplasms Acute or chronic parotitis
Visceral (VS)	Hyoid to mediastinum, anterior to PVS, medial to CS	Thyroid and parathyroid glands, larynx, hypopharynx, trachea, esophagus	Thyroid nodules, thyroid cancer, parathyroid adenoma, mucosal SCC, chondrosarcoma, diverticula
Carotid (CS)	Carotid sheath, enclosed by all three layers of DCF, skull base to aortic arch (SHN + IFN)	SHN: ICA, IJV, CN 9–12 IFN: CCA, IJV, CN 10 (vagus)	Vascular pathology related to carotid (aneurysm, dissection, arteritis) or jugular vein (thrombosis or thrombophlebitis) Nerve sheath tumors Paragangliomas
Retropharyngeal (RPS)	Skull base to T3, between visceral and alar fascia	Fat and lymph nodes	Metastatic lymph nodes (NPC, thyroid, hypopharynx, lymphoma) Suppurative lymph nodes (children) Effusion
Perivertebral (PVS)	Skull base to T4, posterior to RPS	Prevertebral muscles, vertebral bodies, scalene muscles, brachial plexus roots, phrenic nerve, vertebral artery and vein	Discitis/osteomyelitis, longus colli tendinitis, Primary bone tumors (chordoma, ABC, osteoma, giant cell) Vertebral metastases Sarcomas Nerve sheath tumors

1. SCC squamous cell carcinoma, NPC nasopharyngeal carcinoma, ABC aneurysmal bone cyst, SHN suprahyoid neck, IFH infrahyoid neck, ICA internal carotid artery, CCA common carotid artery, IJV internal jugular vein

Take-Home Messages

• The three layers of the deep cervical fascia define spaces, each with unique contents and pathology.

• These spaces can be grouped as suprahyoid or infrahyoid, with some spaces, like the carotid and retropharyngeal spaces, spanning both levels.

• Displacement of the parapharyngeal fat can help determine the site of origin of a suprahyoid mass.

• The visceral space is the only space contained entirely in the infrahyoid neck, and it contains the thyroid and parathyroid glands as well as portions of the aerodigestive tract below the oropharynx.