The normal appearance of the posttherapy neck after common surgical procedures and chemoradiation therapy is presented, with specific details for each surgical procedure. Subsequently, the authors emphasize the recognition of complications and disease recurrence with illustrated examples.
Key Points
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Assessment of the posttherapy neck creates compound challenges because of alterations in normal anatomy that usually provide a framework for interpretation for the radiologist.
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Interpreting imaging in the immediate postoperative period is often complicated by a variety of normal trauma-related changes involving the soft tissue in and around the operative bed: subcutaneous emphysema, edema, hemorrhage, cellulitis, and lymph or suppurative fluid collections.
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The imaging appearance of flap reconstruction depends on the specific surgery performed. In general, the nerve supply to myocutaneous flaps is interrupted, which in combination with disuse leads to muscular fatty atrophy.
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Changes from radiation therapy are visible on posttreatment CT and MRI, most pronounced in the first month or two after irradiation, and may include thickening of the skin and platysma muscle, retropharyngeal edema, postradiation sialadenitis, lymphatic tissue atrophy, and thickening and increased enhancement of the pharyngeal walls and of the laryngeal structures.
Introduction
Imaging has always played an important role in pretherapy assessment of head and neck cancer providing crucial information on the anatomic extent of primary tumors, lymph nodal metastases, and involvement of critical adjacent structures that can preclude surgical resection. Although assessment of the pretherapy neck has its own challenges (eg, poor contrast enhancement in tumors causing difficulty in margin delineation), these are only compounded in the posttherapy neck because of alterations in normal anatomy that usually provide a framework for interpretation for the radiologist. This article discusses the normal appearance of the posttherapy neck after common surgical procedures and chemoradiation therapy. The recognition of complications and disease recurrence is emphasized with illustrated examples.
The postsurgical neck
Types of Neck Dissection
Although there are a variety of classification schemes for the surgical management of neck disease in head and neck cancer, the nomenclature most widely used is the one developed by the Committee for Head and Neck Surgery and Oncology of the American Academy of Otolaryngology/Head and Neck Surgery. It is based on the concept that a full radical neck dissection (RND) is the standard for treating nodal cervical disease in patients with head and neck cancer, and all other procedures involve one or more modifications of the RND. There are five limited surgeries that involve the preservation of one or more nonnodal structures or nodal groups : (1) modified RND (MND), (2) supraomohyoid selective neck dissection (SND), (3) lateral SND, (4) posterolateral SND, (5) anterior compartment SND.
The option to perform a more extensive operation than the full RND also exists, and is referred to as an extended RND. On occasion surgeries do not precisely fit into this classification scheme because certain nodal levels were or were not resected, and should be described accordingly. If MND is performed for limited disease in an N1 or N2 neck, the nonnodal structures spared should be specifically mentioned in the report.
RND
The imaging-based numerical cervical lymph node classification scheme devised by Som and colleagues as a radiologic adjunct to the widely accepted clinically based scheme devised by the American Joint Committee on Cancer and the American Academy of Otolaryngology-Head and Neck Surgery is used in this article. In the setting of extensive neck disease, with or without extracapsular nodal spread, RND is the operation of choice and is often followed by radiation therapy (RT) (the effects of radiation as it pertains to imaging are described later). Traditionally, this applies to patients with disease surrounding the spinal accessory nerve (SAN) or the internal jugular vein (IJV). The procedure includes en bloc resection of all ipsilateral cervical lymph nodes extending from the body of the mandible superiorly to the clavicle inferiorly, and from the lateral border of the sternohyoid muscle, hyoid bone, and contralateral anterior belly of the digastric muscle anteriorly to the anterior border of the trapezius muscle posteriorly. Included along with the levels I through V lymph node groups are the ipsilateral SAN, IJV, submandibular gland (SMG), and sternocleidomastoid muscle ( Fig. 1 ).
MND
MND is performed in patients with limited nodal disease not fixed to or directly infiltrating the aforementioned nonlymphatic structures. The MND involves en bloc resection of lymph node groups I through V, but spares one or more of the ipsilateral nonlymphatic structures removed during RND: the SAN, IJV, SMG, and SCM ( Fig. 2 ). As such, it is important to specifically mention what structures were preserved when describing an MND, either surgically or for imaging follow-up. The major advantage of an MND is related to morbidity encountered when the SAN is removed. Morbidity related to SCM or IJV resection is more relevant when bilateral neck dissections are required.
SND
SND is performed in N0 patients at risk for lymphatic spread of disease. The rationale for SND is based on anatomic studies performed by Rouviere and Fisch and Sigel and clinicopathologic studies performed by Lindberg, Skolnik and coworkers, and Shah, demonstrating that lymphatic drainage of the mucosal surfaces in the head and neck follow relatively predictable routes, and therefore removal of selective high-risk lymph node groups based on the location of the primary lesion can be performed to better preserve functionality and cosmesis. The four types are described next according to the nodal groups resected.
Supraomohyoid SND
Supraomohyoid SND is performed in patients with oral cavity cancer and N0 necks. It involves en bloc resection of level I, II, and III lymph nodes; and whenever level I lymph nodes are resected, the ipsilateral SMG is also removed to control spread of disease ( Fig. 3 ). For tongue carcinoma, the dissection is extended to the level IV lymph nodes, referred to as an extended supraomohyoid SND. Contralateral neck dissection is indicated for cancers in the floor or the mouth, ventral tongue, or midline tongue involvement when postoperative RT is not planned.
Lateral SND
Lateral SND is performed in patients with oropharynx, hypopharynx, and supraglottic larynx carcinomas with N0 necks. It involves en bloc resection of the level II, III, and IV lymph nodes, and is typically performed on both sides because visceral midline neck structures have bilateral lymphatic drainage ( Fig. 4 ).
Posterolateral SND
Posterolateral SND is performed in patients with cutaneous malignancies and soft tissue sarcomas of the posterior scalp, nuchal ridge, occiput, or posterior upper neck. The dissection consists of en bloc removal of levels II through V and the suboccipital and postauricular nodes. Perifacial and external jugular nodes may also be resected. The intervening subcutaneous fat and fascia between lymph node groups and the primary disease are removed to eliminate small nests of tumor cells.
Anterior compartment SND
Anterior compartment SND is performed in patients with cancers of the thyroid gland, hypopharynx, cervical trachea or esophagus, and subglottic larynx. The dissection consists of en bloc removal of the level VI lymph nodes, extending from the hyoid bone superiorly, the carotid sheaths laterally, and the suprasternal notch inferiorly. If there is known disease near the suprasternal notch, level VII nodes are also resected. Occasionally, this can be performed as a unilateral procedure, eliminating the need for parathyroid reimplantation.
Extended RND
Extended RND refers to removal of one or more lymph node groups or nonlymphatic structures not included in a routine RND. This may include retropharyngeal, superior mediastinal (VII), perifacial, and paratracheal (VI) nodes. Examples of nonlymphatic structures that may be included in an extended RND are carotid artery, hypoglossal nerve, vagus nerve, and paraspinal muscles. Special mention of retropharyngeal nodes should be made, either as a pertinent positive or negative finding, with pretreatment imaging of primary pharyngeal carcinomas, and tongue base, tonsillar, soft palate, and retromolar trigone cancers that have spread to the lateral or posterior oropharyngeal walls.
Routine postoperative imaging changes
Interpreting imaging in the immediate postoperative period (before 4–6 weeks) is often complicated by a variety of normal trauma-related changes involving the soft tissue in and around the operative bed: subcutaneous emphysema, edema, hemorrhage, cellulitis, and lymph or suppurative fluid collections. In most cases these changes minimize by 4 to 6 weeks with return to a near normal postsurgical appearance of the neck. However, in some cases the edematous changes, skin thickening, and fluid collections can persist for months or even years after surgery. This tends to occur more commonly in patients who have received postoperative RT or have diminished healing capacity from any cause.
On CT, the primary findings within the subcutaneous fat include reticular soft tissue stranding related to obstructed venules and lymphatic capillaries and a generalized increase in the fat attenuation secondary to increased interstitial fluid. The latter is typically not appreciated with MRI. These treatment-related changes typically resolve within the first month after surgery. However, the onset of reticular fat stranding may be delayed in patients that receive postoperative RT. Hematomas, serosanginous, and chylous fluid collections are not uncommon in the immediate postoperative period and should recede over time. Maturational changes of blood products may be appreciated early on, including relatively high attenuation hematomas in the first couple of weeks (60–90 Hounsfield units), which gradually contract and become near water attenuation (0 Hounsfield units) with ongoing hemolysis and release of methemoglobin into solution.
Vertical skin incisions are typically seen as a small infolding of the skin using axial imaging techniques. Although recurrence could potentially look like this, the diagnosis should be clinically evident. Horizontal incisions are typically not well seen with axial image acquisition. Identifying a SND with imaging can be difficult. The best clue is often reduced subcutaneous fat volume in the region of surgery. MND and RND should be easily identifiable by imaging with flattening of the ipsilateral neck contour, nonvisualization of ipsilateral lymph nodes, and absence of all or some of the ipsilateral SCM, SMG, and IJV. Although the SAN cannot be directly visualized with imaging, the effects of SAN denervation are often present, and include shoulder drooping, atrophy of the ipsilateral upper trapezius muscle, and compensatory hypertrophy of the ipsilateral levator scapulae muscle.
Surgery with reconstruction
There are two broad categories of surgery for head and neck cancer: primary disease resection with an appropriate nodal dissection that does not require reconstruction, and those that require surgical reconstruction to close or repair the surgical defect for improved cosmesis or function.
A wide spectrum of pedicle or free flap techniques, grafts, and prosthesis are currently available for surgical reconstruction. Knowledge in this regard is important, because flap reconstructions do add a dimension of complexity to the imaging appearance of the postoperative neck. Recognition of normal changes over time related to the myocutaneous flap reconstruction is crucial so as not to confuse normal postoperative change within the surgical bed, and in the myocutaneous flap, with disease recurrence.
Pedicle Flaps
These consist of rotated regional skin and its underlying muscle with a preserved vascular pedicle and primary feeding nutrient vessels. The named vascular pedicle with which the flap is rotated is typically identifiable on surveillance imaging, helping to distinguish it from free flap techniques ( Fig. 5 ). Common donor sites for pedicle flap reconstruction include the ipsilateral chest wall (ie, pectoralis major, trapezius, latissimus dorsi) and the head and neck musculature (ie, temporalis, sternocleidomastoid, and levator scapulae). Because the vascular supply to pedicle myocutaneous flap is excellent, they are typically preferred for closing defects in irradiated necks.
Free Flaps
These can consist of skin, soft tissue, muscle, and sometimes bone, and are transferred from distant sites to the surgical field for reconstruction, where they are anastomosed to local vessels using microvascular techniques. In these cases there is no identifiable vascular pedicle with imaging. Examples of free flap reconstructions include cutaneous flaps for oral cavity defects; osseous flaps for mandibular reconstruction; and neopharynx creation using myocutaneous flaps (most commonly pectoralis major pedicle flaps) or jejunal interposition after laryngopharyngectomy.
The imaging appearance of flap reconstruction depends on the specific surgery performed. In general, the nerve supply to myocutaneous flaps is interrupted, which in combination with disuse leads to muscular fatty atrophy. This takes time, and early surveillance imaging may demonstrate relative preservation of muscle bulk in the transposed graft. Curvilinear soft tissue densities within myocutaneous flaps years after surgery are characteristic of atrophic muscle, which needs to be recognized to avoid potential false positivity. Mild overlying skin thickening of surgical flaps is a common finding. Neopharyngeal reconstruction using a pectoralis major myocutaneous flap has a characteristic appearance in which the flap has a rolled or tubular appearance resulting in a reversal of tissue planes, with the skin forming the inner pseudomucosal layer of the neopharynx.
RT
Depending on the clinical scenario, RT (with or without chemotherapy) is not only used as an adjunct to surgery, but also as an effective primary treatment approach in certain cases. The doses delivered, radiation ports, and timing of radiation administration are tailored to the patient and the status of their primary and secondary cervical disease. Changes from RT are visible on posttreatment CT ( Fig. 6 ) and MRI, and may include the following :
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Thickening of the skin and platysma muscle
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Reticular soft tissue thickening within subcutaneous and deep fat planes
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Retropharyngeal edema
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Postradiation sialadenitis: increased enhancement of major salivary glands followed by relative glandular atrophy
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Lymphatic tissue atrophy of lymph nodes and Waldeyer tonsillar ring
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Thickening and increased enhancement of the pharyngeal walls
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Thickening of the laryngeal structures
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Fatty marrow replacement in vertebrae contained within the radiation portal
