CT ANATOMY OF THE NECK SPACES

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CT NECKA PRACTICAL APPROACH

Dr. Hazem Abu Zeid Yousef (MD)

May 2007

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INDICATIONS FOR CROSS SECTIONAL IMAGING OF

THE NECK

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STANDARD TECHNIQUE“Scanning protocol”

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NORMAL ANATOMYCervical triangles.Cervical spaces.

Lymph nodes

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The cervical spaces

The cervical spaces of the suprahyoid and infrahyoid neck include the sublingual space, submandibular space, buccal space, parotid space, parapharyngeal space, carotid space, masticator space, pharyngeal mucosal space, visceral space, retropharyngeal space, posterior cervical space, and prevertebral space

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The sublingual space The paired sublingual spaces are located in the

floor of the mouth and are defined by the mandible anteriorly and laterally, the hyoid bone posteriorly, the oral mucosa superiorly, and the mylohyoid muscle inferiorly. Dividing the sublingual spaces are the paired midline geniohyoid muscles, and the paired genioglossus muscles. Separating these muscles sagittally is a midline low density plane or septum. Lateral to the genioglossus muscles is a lateral low-density plane that contains fat, the submandibular duct, and the sublingual salivary glands.

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Typical lesions seen in the sublingual space include carcinomas extending from the floor of the mouth and tongue; ranulas, which are

retention cysts of the sublingual salivary gland; dermoids and epidermoids;

hemangiomas and lymphangiomas; lingual thyroid glands and thyroglossal duct cysts;

abscesses; lymphadenopathy; and calculi in the submandibular duct

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Submandibular Space

The submandibular space is posterolateral to the sublingual space and contains the superficial lobe of the submandibular salivary gland and lymph nodes. The submandibular space communicates freely with the sublingual. Congenital lesions such as cystic hygromas, branchial cleft cysts, dermoids, epidermoids, and thyroglossal duct cysts may occur in the submandibular space. Abscesses are associated with skin thickening, edema of the fat, and gas in over 50% of cases. Calculi commonly occur in the submandibular glands. Tumors of the submandibular gland, present as soft-tissue masses within the gland. The submandibular lymph nodes are important sentinels in the spread of floor of mouth infections and malignancies and may be involved with lymphom

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Buccal Space

The buccal space is a small region anterior to the masseter and lateral to the buccinator muscle. This space contains the buccal fat pad and is most commonly involved with infection. Deeply invasive skin cancers also may involve this space.. Infections and neoplasms from adjacent spaces, such as the parotid and masticator space, also may secondarily involve the buccal space

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Parotid Space

The parotid space is located posterior to the masseter muscle. This space extends from the external auditory canal and the mastoid tip superiorly to the angle of the mandible below. It contains the parotid gland, intra- and extra-parotid lymph nodes. The gland contains about 20 intraglandular lymph nodes which are considered normal if their transverse diameter is less than 8 mm. The gland also contains extracranial branches of the facial nerve, and vessels: the external carotid artery and the retromandibular vein just behind the mandibular ramus

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Evaluation of masses within the parotid region begins with determination of the lesion as intraparotid or extraparotid. Lesions are considered intraparotid if 50% or greater of the circumference is surrounded by parotid tissue and the epicenter is lateral to the parapharyngeal space. Intraparotid masses displace the parapharyngeal fat medially. Identification of a fat plane between the lesion and the parotid indicates a parapharyngeal space site of origin, whereas direct contiguity of mass to gland indicates a deep parotid lobe origin.

Intraparotid lesions must then be localized to either the superficial or deep parotid lobes. The retromandibular vein is chosen as an alternative landmark for demarcation. The margins of the lesion also should be evaluated. Sharply defined margins tend to favor a benign tumor diagnosis, whereas indistinct margins favor a malignant or inflammatory diagnosis. Finally, determination of the number of lesions is helpful in suggesting a diagnosis.

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Parapharyngeal Space The parapharyngeal space is shaped like an inverted pyramid and extends from the skull base to the hyoid bone. This space is triangular on transaxial images with the apex pointing towards the nasopharynx. Anterolaterally, it is bounded by the medial pterygoid fascia, which separates it from the masticator space. Medially, the parapharyngeal space is bordered by the pharyngobasilar fascia. At the level of the nasopharynx, this space is subdivided into prestyloid and poststyloid compartments. The prestyloid compartment contains branches of the internal maxillary and ascending pharyngeal arteries, fat, salivary rests, and minor salivary glands. The poststyloid compartment is also known as the carotid space as it extends below the hyoid bone.

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Carotid Space The cylindrical carotid space extends from the base of the skull to the aortic arch. The suprahyoid portion of the carotid space is bordered anteromedially by the pharynx, posteriorly by the prevertebral fascia, and anterolaterally by the prestyloid parapharyngeal space. In the infrahyoid region, this space is surrounded by the visceral and retropharyngeal spaces medially, the prevertebral and posterior cervical spaces posteriorly, and the sternocleidomastoid muscle anterolaterally. The carotid space contains the carotid artery, internal jugular vein, glossopharyngeal nerve, vagus nerve, spinal accessory nerve, hypoglossal nerve, sympathetic chain, and the internal jugular nodes of the deep cervical chain.

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Masticator Space This space contains the mandible, the muscles of mastication, and the mandibular division of the trigeminal nerve. Lesions derived from these tissues include nerve sheath tumors, mandibular and soft tissue sarcomas, dental tumors, cysts and abscesses, osteomyelitis, hemangiomas, lymphangiomas, and lipomas.. The mandibular branch of the trigeminal nerve exits the skull through the foramen ovale, which is located above the masticator space and has been termed the "chimney of the masticator space". Lesions within the masticator space can invade the middle cranial fossa by this route and intracranial processes, such as meningiomas, can descend into the masticator space and become extracranial. Signs of perineural spread along the mandibular division of the trigeminal nerve include: expansion of the foramen ovale, mass within Meckel's cave, lateral bulging of the cavernous sinus, and atrophy of the muscles of mastication.

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Pharyngeal Mucosal Space The pharyngeal mucosal space includes the mucosal surfaces and immediate submucosa of the nasopharynx, oropharynx, oral cavity, and hypopharynx. Most of this space is surrounded posteriorly and laterally by a sleeve comprised of the middle layer of the deep cervical fascia. Superiorly, this fascia envelopes the posterior aspect of the pharyngobasilar fascia, which attaches the pharynx and superior constrictor muscle to the base of the skull. Also included in this space are lymphoid tissue, minor salivary glands, and pharyngeal constrictor muscles.

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The nasopharyngeal portion of the pharyngeal mucosal space extends from the posterior boundary of the nasal cavity to a plane defined by the hard and soft palate. For purposes of cancer staging, the nasopharynx is subdivided into posterior, superior, lateral, and anterior walls26. The oropharyngeal portion extends from the inferior margin of the nasopharynx to the level of the glossoepiglottic folds. It is subdivided into lateral, posterior, anterior, and superior walls. The oral cavity consists of the floor of the mouth, the anterior two thirds of the tongue, the buccal mucosa and gingiva, the hard palate and retromolar trigone. The hypopharynx is considered in the section on the visceral space because of its relationship with the larynx.

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Visceral Space The midline visceral space is enclosed by the middle layer of deep cervical fascia and extends from the hyoid bone to the mediastinum. It contains the larynx and hypopharynx, the thyroid and parathyroid glands, the trachea and esophagus, paratracheal lymph nodes, and the recurrent laryngeal nerves.

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The most common malignant lesion of the pharyngeal mucosal space is carcinoma. The lymphoid tissue of the pharyngeal mucosal space includes the adenoids and tonsils and is collectively named Waldeyer's ring. Normally, the lymphoid tissue is asymmetric and involutes with age; therefore, the consideration of neoplasm in a young patient must be carefully weighed with a history of recent upper respiratory infection and the likely presence of normal variability. Non-Hodgkin lymphomas develop from this tissue. Inflammatory lesions such as tonsillar abscess also are fairly common and can present with sore throat, high fever, and a mass in the tonsillar region. Post-inflammatory calcifications frequently are seen as incidental findings on CT

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Retropharyngeal SpaceThe retropharyngeal space lies posterior to the visceral space. The retropharyngeal space extends from the base of the skull to the mediastinum and serves as a potential conduit for spread of neck pathology into the chest. The retropharyngeal space is divided into suprahyoid and infrahyoid compartments. The suprahyoid compartment contains lymph nodes and fat, whereas the infrahyoid compartment only contains fat. Therefore, retropharyngeal lymphadenopathy only occurs above the hyoid and tends to remain unilateral or bilateral, sparing the midline. In contradistinction, infections and direct invasion of cancer may involve both the suprahyoid and infrahyoid portions and the midline "danger space“.

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Retropharyngeal masses lie anterior to the prevertebral space, posteromedial to the parapharyngeal space and medial to the carotid arteries. The prevertebral muscles may be compressed and laterally splayed. Common retropharyngeal lesions include inflammatory lymphadenopathy and abscesses.

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Posterior Cervical Space The posterior cervical space abuts the carotid space posterolaterally and is sandwiched by the sternocleidomastoid muscle anterolaterally and the paraspinal muscles posteromedially The primary components of this space are fat, the spinal accessory and dorsal scapular nerves, and the spinal accessory lymph nodes of the deep cervical chain. Typical lesions arising in this space include spinal accessory lymphadenopathy from metastatic squamous carcinoma and lymphoma, lipomas, liposarcomas, cystic hygromas, and branchial cleft cysts.

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Prevertebral "perivertebral" Space The prevertebral space is formed by the deep cervical fascia. Fascia attaches to the transverse processes of the cervical vertebra dividing this space into anterior and posterior compartments. The anterior compartment contains the vertebral bodies and spinal cord, the vertebral arteries, phrenic nerve, and prevertebral and scalene muscles. The posterior compartment contains the posterior vertebral elements and paraspinous muscles.. Prevertebral space lesions usually arise in the vertebral body, intervertebral disc spaces, or prevertebral or paraspinous muscles. Examples include vertebral osteomyelitis and metastases, and rarer lesions such as chordoma and nerve sheath tumors. On imaging, prevertebral lesions anteriorly displace the retropharyngeal space and anterior border of the prevertebral muscles and posterolaterally displace the posterior triangle fat.

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Cervical lymph nodes

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The outer ring forms the table surface and represents the “sentinel chains” at the base of the skull including the occipital, mastoid, parotid, submandibular, facial, submental, and sublingual nodal groups. The shaded inner C-shaped structure represents the deep retropharyngeal nodes that extend to the hyoid bone. All of these groups drain into the paired anterior and lateral chains depicted as the legs of the table.

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The submental group is located inferior to the anterior mandible and mylohyoid muscle and between the digastric muscles

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The submandibular group is located in the submandibular space.

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The retropharyngeal nodes are located in the suprahyoid retropharyngeal space, along the lateral borders of the longus capitis muscle

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The sublingual nodes are found in the sublingual space and drain the tongue and floor of mouth. A lateral group follows the course of the lingual artery and a median group lies between the genioglossus muscles

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The lateral cervical chain is subdivided into the superficial and deep lateral cervical nodes. The superficial group follows the course of the external jugular vein, is easily palpable, and therefore is not usually examined by imaging. The important deep group is further divided into the spinal accessory, transverse cervical, and internal jugular groups. The spinal accessory nodes are found within the fat of the posterior cervical triangle and posterior cervical space lateral and posterior to the spinal accessory nerve between the trapezius and the sternocleidomastoid muscles. The transverse cervical group are seen in the supraclavicular region.

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The internal jugular group is deep to the sternocleidomastoid muscle and follows the course of the internal jugular vein. High internal jugular nodes extend from the base of the skull to the carotid bifurcation “hyoid bone”. The middle jugular nodes extend from the carotid bifurcation to the omohyoid muscle “ cricoid cartilage”. Finally, the low jugular nodes span from the omohyoid muscle to the clavicle. The nodes of Virchow are the most inferior nodes in the deep cervical chain

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Level I consists of the submental and submandibular nodes. Level II includes the internal jugular chain extending from the base of skull to the (hyoid bone). Level III corresponds to the internal jugular nodes from the carotid bifurcation to the (cricoid cartilage). Level IV refers to all nodes in the internal jugular group from the omohyoid muscle to the clavicle. Level V consists of spinal accessory and transverse cervical nodes. Level VI contains the pretracheal, prelaryngeal, and paratracheal nodes. Level VII includes the nodes in the tracheoesophageal groove and upper mediastinum.

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Imaging criteria for lymphadenopathy is based on nodal size, internal heterogeneity, presence of clusters, shape, and associated findings. Nodes in levels I and II generally are larger compared with nodes in lower levels. Internal lymph node heterogeneity is one of the most reliable criteria for recognizing lymphadenopathy. Clusters are defined as three or more contiguous, ill-defined nodes within the same level ranging from 8 to 15 mm in size. Clusters may be seen in inflammation, cancer, or lymphoma. Small cancerous nodes, seemingly normal by size criteria, may be clustered with larger obviously malignant nodes. Shape is no longer thought to be reliable in differentiating normal from pathologic nodes. Round nodes tend to be neoplastic whereas elliptical or bean-shaped nodes are generally normal or hyperplastic; however, many exceptions may be encountered.

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Thank you