Indian Journal of Radiology and Imaging Indian Journal of Radiology and Imaging

HEAD AND NECK SYMPOSIUM
Year
: 2012  |  Volume : 22  |  Issue : 3  |  Page : 195--208

Imaging in oral cancers


Supreeta Arya1, Devendra Chaukar2, Prathamesh Pai2,  
1 Department of Radio diagnosis, Tata Memorial Hospital, Mumbai, Maharashtra, India
2 Department of Surgical Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India

Correspondence Address:
Supreeta Arya
Department of Radiodiagnosis, Tata Memorial Hospital, Parel, Mumbai 400 012
India

Abstract

Oral cavity squamous cell cancers form a significant percentage of the cancers seen in India. While clinical examination allows direct visualization, it cannot evaluate deep extension of disease. Cross-sectional imaging has become the cornerstone in the pretreatment evaluation of these cancers and provides accurate information about the extent and depth of disease that can help decide the appropriate management strategy and indicate prognosis. Early cancers are treated with a single modality, either surgery or radiotherapy while advanced cancers are offered a combination of surgery, radiotherapy and chemotherapy. Imaging can decide resectability, help plan the precise extent of resection, and indicate whether organ conservation therapy should be offered. Quality of life issues necessitate preservation of form and function and pretreatment imaging helps plan appropriate reconstruction and counsel patients regarding lifestyle changes. Oral cavity has several subsites and the focus of the review is squamous cancers of the gingivobuccal region, oral tongue and retromolar trigone as these are most frequently encountered in the subcontinent. References for this review were identified by searching Medline and PubMed databases. Only articles published in English language literature were selected. This review aims to familiarize the radiologist with the relevant anatomy of the oral cavity, discuss the specific issues that influence prognosis and management at the above subsites, the optimal imaging methods, the role of imaging in accurately staging these cancers and in influencing management. A checklist for reporting will emphasize the information to be conveyed by the radiologist.



How to cite this article:
Arya S, Chaukar D, Pai P. Imaging in oral cancers.Indian J Radiol Imaging 2012;22:195-208


How to cite this URL:
Arya S, Chaukar D, Pai P. Imaging in oral cancers. Indian J Radiol Imaging [serial online] 2012 [cited 2019 Nov 19 ];22:195-208
Available from: http://www.ijri.org/text.asp?2012/22/3/195/107182


Full Text

 Introduction



Oral cancers form nearly 30% of the cancers presenting at our tertiary referral institute, the age adjusted incidence in India being 20 per 100,000 population. [1] Squamous cell cancers (SCC) form the bulk (more than 90%) with tobacco chewing and alcohol being the dominant causes. Imaging provides crucial information for appropriate management of these cancers. Awareness of specific issues related to spread of oral cancers at various subsites and the principles of management would help the radiologist choose an optimal method of imaging and provide the clinician with a relevant report. In this article we will focus on SCC of the gingivobuccal complex and oral tongue.

 Methods



References for this review were identified by searching Medline and PubMed databases. Only articles published in English language literature were used. The search terms used were CT oral squamous cancers, CT MRI buccal cancers, mandibular invasion oral cancers, gingivobuccal cancer, retromolar trigone, imaging neck node metastases, neck node dissection, MRI tongue, MRI tongue tumor thickness, and diffusion-weighted imaging neck nodes. Cross references from relevant articles were also included. This review is evidence based, but also reflects our experience in the management of oral cancers at the largest tertiary referral cancer center in India.

 Anatomy of the Oral Cavity



The oral cavity extends from the lips to a circular region behind, comprising of the circumvallate papillae on the tongue dorsum, anterior tonsillar pillars on either side, reaching upto the junction of hard palate and soft palate superiorly. The papillae are not identified on imaging.

The oral cavity is divided into a central part "the oral cavity proper" and a lateral part "the vestibule" [Figure 1]. The oral cavity proper consists of the central tongue, the roof formed by the hard palate, the lateral walls by the upper and lower alveolus covered by gingival mucosa, and the floor which is chiefly formed by the mylohyoid muscle. The vestibule is a cleft lined by the buccal mucosa laterally, superiorly and inferiorly by reflections of the buccal mucosa onto the mandible and maxilla, respectively, referred to as the upper and lower gingivobuccal sulci (GBS), the gingival mucosa medially [Figure 1], the lips anteriorly and leads to the retromolar trigone posteriorly.{Figure 1}

The retromolar trigone (RMT) is a mucosal fold extending behind the mandibular last molar along the ascending ramus of the mandible upto the maxillary last molar on either side [Figure 2]. It is triangular in shape with base behind the mandibular last molar and apex at the maxillary tuberosity. [2] Beneath the mucosal fold lies the pteryomandibular raphe that attaches superiorly to the pterygoid hamulus and inferiorly to the posterior end of the mylohyoid line. On CT images the RMT is seen in two or three consecutive axial sections, the upper limit behind the maxillary last molar and the lower limit behind the mandibular last molar. The RMT can be seen in its entirety in the oblique plane that can be reformatted with MDCT [Figure 2]A.{Figure 2}

Lateral to the buccal mucosa is the buccomassteric region or buccal space which though not a part of the oral cavity needs mention. Squamous cancers arising from the buccal mucosa often spread to this region and beyond into the masticator space upstaging disease. The buccomasseteric region is bounded by the buccinator medially and the zygomaticus major laterally while the masseter is located posteriorly [Figure 3]. It consists of the buccal fat, angular branch of the facial artery, facial vein, buccal artery, nerves (not identified on imaging), the terminal part of the parotid duct and the facial node. Superiorly this space leads to the masticator space with often incomplete fascial boundaries between.{Figure 3}

The oral tongue located in the central part of the oral cavity is composed of numerous muscles wrapped in mucous membrane. It is formed by the anterior two-thirds of the tongue upto the circumvallate papillae while the posterior one-third of the tongue, also called base tongue is a part of the oropharynx. The midline lingual septum divides the tongue into equal halves, consisting of the intrinsic and extrinsic muscles.

The four intrinsic muscles which form the bulk of the tongue are superior and inferior longitudinal, transverse and vertical. These interdigitate with each other in the upper portion of the tongue. They are difficult to appreciate on CT, but are well seen on MR imaging [3] [Figure 4]. The four extrinsic muscles of the tongue are genioglossus, hyoglossus, styloglossus and palatoglossus, best seen on T2W MR images. They provide attachment of the tongue to hyoid bone, mandible and styloid process. The largest is the fan-shaped genioglossus that originates from the superior genial tubercle, located on the inner aspect of midline mandible and fans out superiorly to interdigitate with the intrinsic muscles. Inferiorly it attaches to the body of hyoid bone. It is well seen on sagittal, coronal and axial MR images [Figure 4] and [Figure 5]. The hyoglossus are thin flat quadrilateral muscles that course lateral to the genioglossus from the greater cornua of the hyoid bone to the sides of the tongue. The hyoglossus is best appreciated on axial and coronal MR imaging [Figure 6]A and B. The palatoglossus muscle covered by the mucosa forms the anterior tonsillar pillar. It arises from the oral surface of the soft palate and passes anterior to tonsil and downward to blend with the hyoglossus and may not always be appreciated on imaging [3] [Figure 7]A. The styloglossus arises from the styloid process and stylomandibular ligament, passes forwards and interdigitates with the hyoglossus [Figure 7]B.{Figure 4}{Figure 5}{Figure 6}{Figure 7}

The floor of the mouth (FOM) is formed primarily by the mylohyoid which is a U-shaped sling extending from one mylohyoid ridge on the inner aspect of the mandible to the other ridge. Anteroposteriorly it extends from the symphysis menti to the last molar tooth. It inserts both into the midline fibrous raphe and the hyoid bone and is best seen on coronal planes on both CT and MR imaging [Figure 8]. The submandibular gland is located inferior to the mylohyoid [Figure 7]A. The deep lobe of the submandibular gland wraps around the posterior free border of mylohyoid to lie on the superior surface of the mylohyoid. However, surgically the FOM is the space between the mucous membrane of the FOM and the mylohyoid. [3]{Figure 8}

Two other muscles, geniohyoid and anterior bellies of digastric support the FOM. The paired geniohyoid arising from the inferior genial tubercles run above the mylohyoid in a paramedian position to insert into the hyoid. [3] They are seen best in the sagittal plane on MR images as darkly hypointense structures on T2W images [Figure 8] and [Figure 9]A. The anterior bellies of digastric are seen on the inferior surface of the mylohyoid, best seen on the coronal plane [Figure 8].{Figure 9}

The sublingual space (SLS) is seen superomedial to the mylohyoid and lateral to the genioglossus [Figure 6]A

and [Figure 9]B. [3] It is a fat-filled space and contains the sublingual gland, deep part of submandibular gland, Wharton's duct, lingual neurovascular bundle [Figure 10]A and the anterior fibers of hyoglossus. On CT it appears as a low density plane [Figure 10]B while on MRI it is seen as a hyperintense area [Figure 9]B.{Figure 10}

 Management of Oral Cancers



Oral cavity comprises of several subsites, which are the lips, buccal mucosa, upper alveolus with gingiva, lower alveolus with gingiva, RMT, oral tongue (anterior two-thirds), FOM and hard palate. Management of oral cavity SCC depends on the stage of disease. [4],[5] Stage I and II cancers (T1-T2, N0) are treated with single modality therapy, surgery or radiotherapy (RT) for the primary, the former being favored. Management of the neck is discussed in the section on neck node metastases. Locally advanced cancers (Stage III and IV) are treated with combination of surgery, radiotherapy and chemotherapy for both primary and the neck.

The 7 th edition of AJCC (2010) staging for oral SCC [5] is provided in [Table 1]. The radiologist should be familiar with T4a (moderately advanced) and T4b (very advanced) subcategories of T4 and provide information indicating T stage and N stage of disease to the clinician. In addition few other specific issues need mention at various subsites that will be dealt in the respective sections.{Table 1}

 Gingivobuccal and RMT SCC



Gingivobuccal SCC include those arising from the buccal mucosa, the gingival mucosa covering the upper and lower alveolus and from the gingivobuccal sulci (together called the gingivobuccal complex). SCC of the lower gingivobucccal complex are the most common oral cancers in the Indian subcontinent due to tobacco chewing and have been described as the " Indian oral cancer". [6]

Important issues in gingivobuccal and RMT SCC that have an impact on management and prognosis are soft tissue spread, bone erosion and nodal involvement.[7],[8] At our institute very early SCC which are seen as superficial ulcers on the buccal mucosa are not imaged for the primary, but are referred for ultrasound evaluation of the neck for nodal status. An ulcerous lesion on the gingival mucosa, however, requires cross-sectional imaging to rule out bone erosion.

All other SCC require more detailed evaluation by imaging. CT and MRI perform comparably for assessment of soft tissue extent, [9],[10],[11] but CT is preferred for evaluating bone erosion. [12],[13] Although several reports have evaluated PETCT in the initial staging of oral cavity SCC, the diagnostic yield of PETCT did not score over anatomical imaging for either the evaluation of the primary or occult nodal metastasis [14],[15] and we do not use it in the initial evaluation of oral SCC. However, the NCCN guidelines suggest a level 2A evidence for use of PETCT in stage III- IV disease that could alter management by demonstrating distant metastases. [5]

Contrast-enhanced multidetector computed tomography (MDCT) combines the advantages of speed of scanning and the ability to use the "puffed cheek" technique for imaging gingivobuccal and RMT cancers [Figure 1] and [Figure 11]. A 16-slice MDCT scanner provides adequate thin slices for isotropic coronal, sagittal and oblique reformations. Bone and soft tissue algorithms are obtained. Puffed cheek technique requires the patient to blow uniformly through pursed lips while breathing normally. [16] The technique can be improved further by pushing the tongue away from the hard palate. [17] {Figure 11}

Soft tissue extension

Gingivobuccal SCC can spread laterally into the overlying buccal and subcutaneous fat upto the skin, superiorly into the maxillary sinus [Figure 12], medially erode the mandible and extend across into the lingual musculature all of which are defined as Stage T4a. [5] They can extend anteriorly into the lips and occasionally spread perineurally through the mental foramen. Postero-superior spread into the masticator space is classified as T4b. [5]{Figure 12}

Involvement of the skin is a clinical finding documented by induration and peau d'orange appearance requiring appropriate reconstruction following resection. This could appear as stranding of the subcutaneous fat on CT and needs mention. However, Spector, et al. noted in a small series that linear reticulations seen on CT in the dermis and subcutaneous fat adjacent to the tumor were more often due to peritumoral inflammation rather than tumor invasion. [18]

Postero-superior spread: Although the AJCC 6 th edition called masticator space involvement (T4b) unresectable, the 7 th edition reclassifies this as very advanced disease. This is because some cases with masticator space involvement may be amenable to resection, while involvement of the skull base and internal carotid artery is definitely unresectable. A recent report compared the outcomes of resection of advanced buccal SCC that had spread to the masticator space. The mandibular notch between the coronoid and conyloid process was used as a line of demarcation and disease classified as supra-notch and infranotch. [19] A subset of T4b with infranotch disease were found to have a more favorable prognosis (local control of 74%) than those with supranotch disease (local control of 42.9%). The distance between the skull base and mandibular notch is 2 cm while the distance between skull base and lower limit of pterygoid plates is 3 cm. [19] Hence the upper part of the pterygoid plates are a supranotch structure while their lower limits are in the infranotch compartment. While seeking information regarding posterior spread, some clinicians are more familiar with the term infratemporal fossa (ITF). The masticator space (MS) well known to the radiologist refers to the compartment formed by splitting of the layers of the investing layer of cervical fascia at the lower border of the mandible. It contains the ramus and posterior body of mandible, masseter, temporalis, medial and lateral pterygoid muscles and the mandibular division of trigeminal nerve, which continues as the inferior alveolar nerve (within the mandible). [3] Although MS and ITF are often used synonymously in the current lexicon for reasons described below, some mention is needed of the subtle difference. The ITF [Figure 13] A-C is a non fascial lined space bounded anteriorly by the posterior surface of the maxilla, posteriorly by the mastoid temporal bone, superiorly by inferior surface of greater wing of sphenoid and squamous temporal bone, laterally by the inner surface of vertical ramus of mandible, and medially from anterior to posterior by the sphenoid pterygoid process, pterygomaxillary fissure and lateral wall of nasopharynx. [20],[21] Inferiorly the anatomical fossa has no floor and ends at the level of angle of mandible. [20] The major contents of the ITF are pterygoid muscles, internal maxillary artery, pterygoid venous plexus [Figure 13]C, and mandibular division of trigeminal nerve. The masseter is not a content of the ITF. The ITF thus combines the medial part of the masticator space, part of the parapharyneal space and the retroantral buccal space. The inferior and superior boundaries of both spaces are at the same levels with the foramen ovale seen in the roof [Figure 13]A.{Figure 13}

Irrespective of the terminology used, in oral cavity SCC it is important to precisely convey the craniocaudal extent of disease spread. Spread of disease into the upper part of the space closer to skull base (high ITF or high masticator space or supranotch disease) constitutes a section of T4b SCC with unfavorable surgical outcomes and surgical morbidity [Figure 14]. The normal high space is easily identified on axial imaging as containing the lateral pterygoid muscle and the upper two-thirds of pterygoid plates [Figure 13]B while the low masticator space contains medial pterygoid and masseter muscles [Figure 13]D. Disease involving low masticator space/low ITF or infranotch compartment comprises a subset of T4b SCC with favorable surgical outcomes and most clinicians prefer to operate this group [Figure 15]A and B.{Figure 14}{Figure 15}

Perineural spread through the foramen ovale may occur and causes foraminal widening on CT [Figure 14]. Perineural spread is, however, best imaged on MRI and may be seen as excessive enhancement within foraminae or loss of normal fat density. [22] RMT SCC can spread to several sites, both circumferentially and superiorly as illustrated in [Figure 16] and [Figure 17].{Figure 16}{Figure 17}

Bone erosion and role of various imaging modalities

Bone erosion by SCC is an adverse prognostic criterion and requires some form of mandibular resection, either marginal or segmental mandibulectomy [Figure 18]A, B. Marginal mandibulectomy involves resection of a part of the superior rim of the mandible. It requires preservation of an at least 1 cm vertical height of the body of the mandible for strength. It ensures that mandibular continuity is maintained and a much better cosmetic and functional end result is achieved. It is offered when subtle erosion is present or when a small soft tissue component abuts the mandible without causing erosion. [6],[23],[24] Segmental mandibulectomy is performed when there is gross erosion and invasion of the inferior alveolar canal [Figure 19]A, extensive paramandibular soft tissue spread [Figure 19]B, in edentulous mandibles (where the height is inadequate) and in irradiated mandibles. [6]

Preoperative imaging needs to comment on absence or presence of mandibular erosion, whether erosion is subtle or gross (buccal, occlusal, and/or lingual cortices and if the marrow and inferior alveolar canal are invaded). The anteroposterior extent of erosion (on axial images) and the height of the uninvolved segment of mandible from the inferior border (on coronal imaging) need to be recorded to plan marginal mandibulectomy [Figure 20]. The oblique reformation best depicts the inferior alveolar canal in the lateral segment of the curved mandible [Figure 18] and [Figure 19]A. Reformations done ad hoc on workstations or on the PACS with spatial cursor localization facilitate confident assessment. Imaging should record sparing of the condyloid process and posterior segment of the mandible which helps plan reconstruction, necessary after segmental mandibular resection.{Figure 18}{Figure 19}{Figure 20}

Numerous prospective and retrospective studies have investigated various imaging methods such as orthopantomogram (OPG), CT scan, Denta scan, MRI, Bone scan and SPECT for assessing mandibular invasion in oral squamous cancers. Comparison has also been made with clinical examination and periosteal stripping. Although initially imaging was pronounced inaccurate as compared to clinical examination, subsequent studies conclusively proved the role of imaging in assessing mandibular invasion. CT was found to have the highest specificity (87%) while SPECT and MRI had the highest sensitivity (96-97%). [9],[25],[26],[27],[28],[29],[30],[31],[32],[33] Two studies have also evaluated MDCT and found a sensitivity of 82.6 % and specificity of 86.9% for mandibular invasion. [34],[35] Vidiri, et al. found no statistically significant difference in accuracy between MRI and MDCT, [34] while another study by Imaizumi, et al. showed that MRI overestimated mandibular cortical erosion and inferior alveolar nerve involvement [13] [Figure 21]. Disadvantages with OPG include inability to image soft tissue, false positives due to periodontitis, inability to assess the symphysis menti region and visibility of erosion only after 30-75% mineral loss. [25] [Table 2] provides a checklist for reporting in gingivobuccal and RMT SCC.{Table 2}{Figure 21}

 Tongue and Floor of Mouth SCC



There is a rising incidence of oral tongue SCC both in India and in the West. This is associated mainly with tobacco and alcohol use, but a small proportion have been associated with HPV infections. [36] Squamous cancers of the oral tongue behave differently from those of the base tongue which are similar to oropharyngeal cancers. This review focuses on oral tongue SCC, the majority of which arise from the lateral border with few from the ventral surface.Imaging for tongue SCC requires a modality with superior soft tissue characterization and hence MRI is the optimal modality, displaying exquisite anatomical detail including intrinsic and extrinsic muscles, the floor of mouth (FOM) and the lingual vascular bundle. [37],[38],[39] CT has insufficient soft tissue characterization and is frequently hampered by dental artefacts.

An optimal MR imaging protocol is incomplete without postgadolinium T1W sequences as the tumor frequently shows intense enhancement and is best depicted on this sequence [40] [Figure 22]. Our protocol on a 1.5 T magnet using a head and neck phased array coil is acquired with axial and coronal spin-echo T1-weighted (TR, 500-600 ms; TE, 7-10 ms); axial and sagittal fast spin-echo T2-weighted (TR, 3000-4000 ms; TE, 90-100ms); coronal short tau inversion recovery (STIR) (inversion time, 150 ms); and postcontrast axial, coronal, and sagittal T1-weighted sequences. The sequences are acquired at 4-mm thickness with 1-mm intersection gap. The matrix used is 256 × 256, NEX 2 and FOV 240 mm. Echoplanar diffusion weighted imaging is performed with b values of 0 and 1000 sec/mm 2.{Figure 22}

Noncontrast T1W sequences demonstrate cortical erosion and marrow invasion. Contrast-enhanced T1W images help assess marrow invasion, [13] perineural spread, soft tissue extent, tumor thickness and best demonstrate necrosis in nodes. T2W sequences depict extrinsic muscle and FOM involvement as well as nodes. [40] STIR images have high sensitivity for visualizing nodes but with reduced specificity. DW images are of added value, particularly in subcentimeter metastatic nodes.

In oral tongue SCC seen as very shallow ulcers, imaging may not be required for the primary, but due to a high incidence of occult cervical lymph node metastasis [5],[41] the neck needs investigation with ultrasonography. In early tumors, the important issue is tumor thickness which has prognostic relevance. A tumor thickness of >4 mm on histopathology (HP) has been associated with increased incidence of cervical nodal metastases. [42]

The value of MRI in staging and measuring the tumor thickness has been established. [43],[44],[45],[46] [Figure 23] depicts measurement of tumor thickness [45] which is a latero-medial and not a craniocaudal dimension for the vast majority of tumors that arise from the lateral border. Lam, et al. found a higher concordance rate for tumor thickness using contrast-enhanced T1W images (83%) than with T2W images (56%) due to peritumoral inflammation seen as hyperintensity with the latter. [45] Okura, et al. evaluated the features of primary tongue SCC on MR imaging to predict cervical nodal metastases and found that a tumor thickness of >9.7 mm was a significant predictor for nodal metastases and proposed that elective neck dissection could be performed in such cases. [47] Intra-oral ultraonography has also been used successfully for measuring tumor thickness. [48],[49]{Figure 23}

MRI can also accurately depict the T stage, another factor with bearing on prognosis and treatment. Extension to the extrinsic muscles (upstaging disease to T4a), encasement of neurovascular bundle, invasion of the FOM and base tongue are well seen [Figure 24] and [Figure 25]. These features influence the choice of therapy (single or multiple modality) and the extent of surgical resection that can vary from wide excision to partial glossectomy to total glossectomy (for tumors involving bilateral neurovascular bundles). The latter procedure can be morbid with poor outcome and often such patients are offered organ preservation therapy (chemotherapy followed by concurrent chemoradiation). Extension of primary tumor upto or across the midline may require bilateral neck dissection or irradiation to address ipsilateral and contralateral neck node metastases [Figure 24]B. Extension to valleculae, pre-epiglottic space and hyoid bone [Figure 25] need to be documented as they are relative contraindications to surgical treatment. This is because removal of hyoid would require at least a supraglottic laryngectomy that necessitates more extensive reconstruction increasing morbidity. Extension to tonsil and lateral pharyngeal wall are also relative contraindications. Therefore precise soft tissue extent depicted by imaging has a significant impact on management. Bone erosion can occur in tongue SCC extending to FOM or primary FOM cancers although seen less frequently than in buccal cancers [Figure 26]. Involvement of the segment of the involved mandible (midline or lateral) needs to be recorded with detailed information as described earlier. Midline invasion of the genial tubercles leading to mid-third mandibulectomy can result in loss of tongue and laryngeal muscle attachments, requiring appropriate reconstruction. Imaging can also assist plan adequate reconstruction after resection. When the tumor involves geniohyoid and mylohyoid, the entire thickness of the FOM needs extensive reconstruction with an anterolateral thigh flap or pectoralis major myocutaneous flap. Involvement of parts of genioglossus and hyoglossus alone can be reconstructed with free radial artery forearm flap [Figure 27]. [Table 3] provides a checklist for reporting in oral tongue and FOM cancers.{Table 3}{Figure 24}{Figure 25}{Figure 26}{Figure 27}

Neck node metastases

Involvement of a single node reduces survival by half. [50] Gingivobuccal and tongue SCC initially spread to level I and II nodes respectively. Skip metastases with tongue cancers to level III and IV and to contralateral I and II levels are also known. When the neck is negative for nodes on clinical examination, it is referred to as the cN0 (clinically negative) neck while the cN+ (clinically positive) neck refers to palpable neck nodes. However clinical examination is unreliable for detection of nodes and the incidence of occult neck nodal metastases even in early oral cancers varies from 16% to 40% in tongue cancers. [41],[42]

The cN+ neck is addressed with modified radical neck dissection. In the cN0 neck, elective neck dissection was proposed when the incidence of nodal metastases was greater than 15-20%. [42] A recent meta-analysis proposed it for all cN0 necks in oral cancers, [51] but the meta-analysis was criticized. [52],[53] A meta-analysis has analyzed numerous imaging modalities for detecting neck nodes and concludes that US-guided FNA is the most reliable technique to assess lymph node metastases in head and neck cancers. [54] Ultrasonography can be used to observe the N0 neck if the decision is not to perform elective neck dissection. The disadvantage of US and guided FNA, however, is the lack of widely available expertise. CT has a sensitivity varying from 55% to 95 % and a specificity of 39%-96% for assessing neck node metastases in various series while the reported sensitivity and specificity for MRI has been 64%-92% and 40%-81%. [54] Newer morphological criteria on T2W MR imaging for assessing neck nodes [55] and reports on diffusion weighted MRI [56],[57] promise increased accuracy of MR imaging for detecting metastatic neck nodes [Figure 28].{Figure 28}

CT or MRI ordered for the primary may detect metastatic nodes that may appear enlarged and rounded, show necrosis [Figure 29], extracapsular spread and invasion of adjacent structures. Necrosis is the most reliable criterion of metastasis. For non-necrotic homogenous nodes, various size criteria using maximum longitudinal diameter and minimum axial diameters have been specified, but false positive and false negative rates of 15-20 % are still seen as metastasis can occur in subcentimeter nodes. [58] The nodes in the draining region of the primary need close scrutiny. Bulky nodes at multiple levels and extranodal spread require postoperative irradiation. Circumferential contact of node with the carotid artery of more than 270 degrees precludes resectability of node and needs mention. [59] This measurement is ideally done using the angle measurement tool on the PACS/workstations. When the angle exceeds 180°, the tool automatically measures the smaller angle and the actual measurement is obtained by subtracting from 360° [Figure 30].{Figure 29}{Figure 30}

To summarize, imaging is essential in the management of oral cancers. It augments clinical findings to plan appropriate therapy. When surgery is contemplated, it provides information about resectability, extent of resection and reconstruction. Information from imaging can also indicate treatment outcomes.

 Acknowledgement



Tata Memorial Hospital.

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