10.2\ Neck Dissection

10.2.1  Discussion

Neck dissection is performed to diagnose and/or remove at risk and/or diseased lymph nodes and, in some cases, surrounding structures. The main types of neck dissection include selective, modified, radical, and extended neck dissection (Table 10.2). Features of each of these can be appreciated on CT (Figs. 10.16, 10.17, 10.18, 10.19, and 10.20).

Postoperative imaging is usually performed with contrast-enhanced CT and serves to identify clinically occult disease, which occurs in 7.5– 28% of cases. Per NCCN guidelines, a baseline study is usually obtained within about 6 months of surgery for comparison with subsequent studies, which are usually obtained depending on symptoms, physical exam, and findings from previous imaging. During the early postoperative period, local hemorrhage and edema are common findings­ for all types of neck dissection. These changes usually resolve by 6 weeks after surgery and have a reticular appearance on CT. Over time, there may be persistence of edema and development of fibrosis, particularly if radiotherapy is administered. The degree of retropharyngeal edema can be exacerbated by resection of the internal jugular vein. A stable postoperative appearance may not be attained until 12–18 months after surgery.

Following selective and modified radical neck dissection, atrophy of the sternocleidomastoid and strap muscles is also common. In addition, removal of the adipose tissue and lymph nodes around the carotid sheath decreases the space between the sternocleidomastoid and internal jugular veins. The presence of scarring may accentuate the degree of asymmetry and effacement of the fat planes. Nonvisualization of the ipsilateral internal jugular vein occurs in about 20% of cases of selective neck dissection and may be attributable to thrombosis and should be reported. Following removal of the ipsilateral submandibular gland with level I dissection, the remaining contralateral submandibular gland should not be misinterpreted as a lesion itself. Radical neck dis-

section results in more conspicuous­ flattening of the neck contour and blurring of the tissue planes than modified radical neck dissection. There may also be reduced flow in the carotid artery due to surgical manipulation and radiation therapy. Rarely, the common carotid artery is sacrificed during extended neck dissection. Myocutaneous flaps are usually required to reconstruct large defects resulting from radical and extended neck dissection. Tissue flaps are also sometimes used to provide coverage of the external carotid artery after modified radical neck dissection.

Potential pitfalls in the interpretation of imaging after neck dissection has been performed are cauterized adipose tissue and suture granulomas, which can be mistaken for lymphadenopathy. Cauterized adipose tissue can appear as nodular foci of soft tissue attenuation, but often conserve some degree of fat attenuation centrally (Fig. 10.21). Suture granulomas can also appear as soft tissue nodules, but the occasional presence of hyperattenuation centrally associated with the suture is a help clue (Fig. 10.22). In either case, these conditions tend to remain static on serial imaging, as opposed to recurrent neoplasm.

Complications depend on the extent of neck dissection. Denervation injury results in high T2 signal and enhancement within the first few months and fatty atrophy and laxity on a chronic basis. The more frequently encountered sites for denervation injury after neck dissection include the trapezius muscle and the tongue (Fig. 10.23). Extensive neck dissection can potentially impair lymphatic drainage and lead to cervicofacial edema, which appears as diffuse swelling and fat stranding (Fig. 10.24) and can be exacerbated by radiation therapy. Leakage of chyle from the lymphatic system can result in lymphoceles, which typically appear as unilocular fluid collections with thin walls (Fig. 10.25). Infections can occur in the skin and subcutaneous tissue as cellulitis and abscesses (Fig. 10.26). In addition, osteomyelitis of the clavicle can result from lower central compartment or supraclavicular lymph node dissection (Fig. 10.27). This should not be confused with degenerative changes and effusions of the sternoclavicular joint due to altered biomechanics and neuropathic joint (Fig. 10.28).

Fig. 10.16  Selective neck dissection. Axial CT image 4 weeks after lateral neck dissection (a) shows a seroma (arrow) overlying the right sternocleidomastoid muscle. There is loss of fat surrounding the carotid artery and subcutaneous tissues. Axial CT image obtained 2 years after right lateral neck dissection and radiotherapy (b) shows

subcutaneous stranding. The sternocleidomastoid muscle and internal jugular vein are intact. Axial CT image (c) shows resection of the right submandibular gland and remaining left submandibular gland (arrow), producing an asymmetric appearance that should not be confused with a mass lesion

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Fig. 10.16  (continued)

Fig. 10.17  Modified radical neck dissection. Axial CT image shows the absence of the right internal jugular vein and atrophy of the sternocleidomastoid (S) and trapezius (T) muscles but compensatory hypertrophy of the right levator scapulae (L). There is also mild edema in the right neck soft tissues

Fig. 10.18  Radical neck dissection. Axial CT image shows the absence of the left sternocleidomastoid and internal jugular vein as well as concavity of the left neck contour

Fig. 10.19  Radical neck dissection with pectoralis rotational flap. Axial CT image shows right radical neck dissection,­ including resection of the right sternocleidomastoid. Instead, there is a pectoralis rotational flap (arrow) that covers the carotid artery

Fig. 10.20  Extended neck dissection. Preoperative axial CT image (a) shows an infiltrative tumor (arrow) that encases the left carotid artery. The patient had undergone prior radical neck dissection and radiation therapy.

Fig. 10.21  Cauterized adipose tissue. Axial CT image shows a nodular area with central hypoattenuation in the subcutaneous tissues of the right face (arrow), which represents biopsy-proven fibroadipose tissue

Postoperative axial CT image (b) shows interval sacrifice of the left common carotid artery and myocutaneous flap reconstruction

Fig. 10.22  Suture granuloma. AxialCT image after total laryngectomy shows a nodule with a central highattenuation focus (arrow)

Fig. 10.23  Denervation related to neck dissection. Coronal STIR (a), T1-weighted (b), and post-contrast fat-suppressed T1-weighted (c) MR images show edema, and enhancement is an atrophic right trapezius muscle

(arrow), ipsilateral­ to where neck dissection was performed. Axial CT image in a different patient (d) demonstrates fatty change in the left half of the tongue (arrow) after hypoglossal nerve sacrifice during neck dissection

Fig. 10.24  Postoperative lymphedema. Sagittal CT image shows diffuse swelling of the cervicofacial soft tissues, particularly the tongue and lips, as well as diffuse fat stranding

Fig. 10.25  Lymphocele. Axial CT image shows a large, unilocular fluid-attenuation collection (*) in the left neck that extends into the left chest subcutaneous tissues (Courtesy of John Wandtke, M.D.)

Fig. 10.26  Wound abscess. There is a large gas and fluid collection in the right neck surgical bed. There is also overlying subcutaneous fat stranding and skin thickening

Fig. 10.27  Osteomyelitis. Axial CT image shows an open wound and sinus tract with regional subcutaneous fat stranding and erosion of the left medial clavicle (arrow)

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Fig. 10.28  Neuropathic joint. Coronal CT image (a) shows radical right neck dissection and flap reconstruction. Axial CT image (b) shows right proximal clavicle degenerative changes ipsilateral to the neck dissection

D.T. Ginat et al.