Ultrasound of the Cheek

Abstract

The cheek is a complex anatomical area, with several multifaceted implications, dealing with otorhinolaryngology, dentistry, dermatology, esthetic medicine, and surgery. In this review we first illustrate the appropriate ultrasound examination technique, providing some specific tips. Then we describe the ultrasound anatomy of the cheek. Subsequently we provide a systematic clinical and sonographic approach to the issue of cheek bump. Then we mention the key abnormalities of the cheek, including inflammatory processes, vascular abnormalities, cysts, tumors, esthetics, and miscellaneous abnormalities. Finally we emphasize the role of ultrasound guidance for diagnostic and therapeutic percutaneous procedures.

Abbreviations

MRI

magnetic resonance imaging

SLEB

subepidermal low echogenicity band

SMAS

superficial musculoaponeurotic system

Follow? Nay, I'll go with thee, cheek by jowl.

William Shakespeare, A Midsummer Night's Dream, Act 3, Scene 2

The cheeks constitute the largest anatomic and esthetic unit of the face, participating in eating, talking, and expression. The fullness of the cheek is made by fat pads, the parotid gland, muscles, and tissues. Ultrasound is regarded as the first modality to study this area, providing the anatomical details and initial characterization of cheek lesions. It also aids in evaluating the need for further cross‐sectional imaging, particularly with magnetic resonance (MRI). MRI is useful for extensive, large lesions, as well as for malignant ones, but in many cases, ultrasound allows a definitive assessment of the abnormality. ¹ This article illustrated the sonographic appearance of the cheek and of the abnormalities that can be encountered in this anatomical area. For the purpose of this review, abnormalities of the bone, parotid gland, and cheek mucosa are excluded.

Methodological Tips for Cheek Examination

Frequencies between 18 and 30 MHz allow an optimal exploration of the epidermis, dermis, and subcutis, but lower frequencies, ranging between 13 and 18 MHz, are required to investigate the deeper structures. ² , ³ We usually start the examination using a relatively lower frequency, linear probes, that generally have a larger footprint and consequently allow a more comprehensive display of the area. Once the abnormal findings are detected, we go into details using higher‐frequency, smaller‐footprint transducers (20–24 MHz). ⁴

Transmission frequency, beam depth, and time‐gain compensation are regulated according to the anatomic position of the area of interest. The beam focus is placed at level, or immediately below the level, of the abnormality. Brightness gain is regulated to maximize image contrast. ⁴ Matrix‐array transducers and spatial compound technology may be useful for the simultaneous display of the different structures of the cheek, placed a different depth. ⁵

Power‐ and color‐Doppler scanning is always included, requiring the scanner to be set adequately to detect slow flows. If available, newer microvascular modalities, working at higher frame rates than conventional Doppler techniques, are preferred. ⁶ , ⁷

The whole anatomical area is accurately explored, using transverse and longitudinal views and gently moving the transducers from top to bottom and from forwards to backwards. Oblique views are employed to examine and measure a focal abnormality according to its long axis. Special attention is always devoted to the perpendicularity of the probe over the patient skin.

Comparison of the affected side with the contralateral one is useful, particularly to identify changes in thickness and echogenicity of the various structures. Dynamic maneuvers may be useful to study the mimic muscles, with scans obtained during instructions such as “smile”, “show your upper incisors,” “bite your teeth together strongly,” or “smile and pull your cheeks inwards.” ⁸

A thick gel layer is placed over the abnormality, particularly in the case of superficial locations. The hand pressure on the probe is minimized, both for B‐mode and Doppler mode, with the probe gently floating over the gel. Gel pad spacers are not employed routinely. These pads may be employed to maximize beam focusing, improve B‐mode and Doppler image quality, and adapt the probe footprint to irregular and deforming surfaces, such as scars. ⁹ However, stand‐off pads may compress the low flow vascularity while recent high‐frequency transducers allow an optimal focus of the most superficial structures.

Scans are usually obtained with the patients in a supine position. However, when investigating aging‐related changes with ultrasound it is suggested to have the patient head in a vertical position. This is because the maximum gravitational displacement of face soft tissues is recognizable in a sitting position. An upright position allows for an objective picture of the participation of the various anatomical tissues to the contour deformities. ¹⁰

Intra‐oral ultrasound, using hockey‐stick probes or even finger‐top probes, has been employed in local staging of oral cavity tumors. ¹¹ For cheek tumors a water mouth distention technique has also been described. ¹² The patient is asked to keep the oral cavity filled with water, like when using a mouthwash (Figure 1). This maneuver improved the ultrasound detection of the tumor and the lesion extension definition.

Figure 1.

Transverse scan of the cheek obtained with the water mouth distention technique. The fluid allows to optimally depict the inner aspect of the cheek. Arrows point to the buccinator muscle. MM, masseter muscle; ZMM, zygomaticus major muscle; T, tooth.

Ultrasound Anatomy of the Cheek

The cheeks form the muscular walls of the oral cavity, located between the zygomatic arch and the orbital‐cheek crease, superiorly, and the lower mandible border, inferiorly. The lateral border is formed by the parotid gland and preauricular crease while the medial border is formed by the nasofacial sulcus, the nasolabial crease, and the labiomandibular creases. The midcheek, particularly, is the specific part of the midface on the anterior aspect of the face, medial to a vertical line from the lateral orbital rim to the oral commissure (Figure 2). ¹³ The cheek can be subdivided into 4 regions: infraorbital, zygomatic, buccal, and parotidomasseteric. ¹⁴

Figure 2.

Schematic drawing of cheek anatomy. 1, parotid gland. 2, masseter muscle. 3, buccinator muscle. 4, orbicularis oris muscle. 5, buccal fat pad.

The cheek, as well as the entire face, is composed of 5 layers: (1) the skin, (2) the subcutaneous layer, (3) the musculoaponeurotic layer, (4) loose areolar tissue (ie, spaces and retaining ligaments), and (5) the fixed periosteum and deep fascia. ¹³ The cheek skin is formed by the epidermis which appears as a thin, hyperechoic line at ultrasound, and by the dermis, slightly thicker and less echoic than the epidermis. ² The dermis thickness ranges from 0.6 to 2.1 mm, according to the different cheek subunits. ¹⁵ The subcutaneous layer (“line 2”) consists of hypoechoic fat lobules and of hyperechoic connective septa. Fibers anchor the dermis to the subcutis and the subcutis to the superficial musculoaponeurotic system (SMAS) layer. The thickness of the subcutaneous fat varies according to the different cheek subunits. Vascular perforators originate from the deep arteries, pass through the SMAS, and penetrate vertically into the subcutis. The third layer of the cheek consisted of the SMAS (“line 3”) and of the superficial layer of the upper and lower group of the mimic muscles. The SMAS anatomical entity and, even, the true existence of this distinct aponeurotic/fascial layer is debated. ¹⁶ SMAS is commonly described as a single, continuous, and thin fibromuscular tissue layer, showing variable fat content. SMAS has no anchorage to the bones below while the fibers of the retinacula cutis anchor it to the subcutaneous tissue and dermis. SMAS is present in the forehead, temporal, parotid, zygomatic, buccal, infraorbital, and mental regions. ¹⁴

The cheek muscles do not form a continuous layer, since fat and connective tissue are present between the muscles. ¹⁷ To simplify, however, these muscles are categorized into a superficial and a deep group. Within the superficial layer are the orbicularis oculi, the levator labii superioris, the levator labii superioris alaeque nasi, the depressor anguli oris, the platysma, the risorius, and the 2 zygomaticus muscles. ¹⁷ The deep muscle layer of the cheek consists of the masseter, buccinator, and levator anguli oris muscles. The lower part of the orbicularis oculi muscle contributes to the superior part of the cheek. The levator labii superioris alaeque nasi muscle demarcates the medial contour of the cheek region. To scan this muscle, the probe is placed in an oblique transverse plane that passes through the nasal crease. The muscle levator labii superioris alaeque nasi will be observed lateral to the nasalis and medial to the levator labii superioris. Rotating the probe to an oblique sagittal plane to observe the muscle along its long axis, with the angular branch of the facial artery running just above. ¹⁴ The levator labii superioris is part of the medial cheek region. The probe is placed in the middle of the inferior orbital rim in the transverse plane, and the muscle is visualized in its short axis, above the infraorbital foramen. Moving downward, the levator labii superioris appears to be placed more medially. ¹⁴ The 2 zygomaticus muscles contribute to the middle cheek. The bony prominence of the malar surface acts as an anatomical landmark. Orienting the scan in a transverse plane a few millimeters caudal to its lateral third, the zygomaticus major muscle is imaged in its short axis while coursing obliquely over the masseter muscle. Shifting the transducer medially allows the demonstration of the thinner zygomaticus minor muscle, located superficially to the maxilla, and the thicker levator labii superioris muscle. ⁵ The 2 zygomaticus muscles may blend and be not distinguishable at ultrasound. ¹⁴ Slightly lower to the zygomaticus muscles lay the risorius muscle and the levator anguli oris muscle. The masseter muscle is the largest one and has a superficial and deep head. The probe is placed along the zygomatic arch in a transverse plane and is subsequently moved caudally to visualize the masseter short axis. Rotating the probe vertically, the masseter bridge between the zygomatic arch and the mandible will be displayed. ¹⁴ The buccinator muscle is the deepest one, close to the oral cavity. The probe is placed transversely over the masseter and then relocated in a more anterior direction to visualize the buccinator in its long axis, between the undersurface of the masseter muscle and the buccopharyngeal fascia. ¹⁴ This also allows the identification of the thin risorius muscle, emerging from the superficial fascia of the masseter superficial head. ¹⁴

The fat of the cheek originates from different regions in the face, but all come at the cheek. The fat compartments of the cheek are categorized into superficial and deep. Superficial compartments include infraorbital, superficial medial, nasolabial, middle cheek, lateral temporal‐cheek, and superior and inferior jowl fat. Deep compartments include the suborbicularis oculi fat (medial and lateral), the deep medial cheek fat (medial and lateral), and the buccal fat. ¹ , ¹⁷ , ¹⁸ , ¹⁹ The buccal fat pad, or Bichat pad, lies above the buccinator muscle (Figure 3). Just below the SMAS there is the thin parotidomasseteric fascia, running over the parotid gland posteriorly and over the masseter muscle anteriorly. The anterior border of the parotid gland passes inferiorly along the masseter muscle and overlies its lateral surface.

Figure 3.

Transverse scan of the midcheek region showing the buccal fat pad. MM, masseter muscle; BM, buccinator muscle; FA, facial artery.

The 3 bones that help form the cheek are the zygomatic bone, the maxilla, and the mandible.

Facial lymph‐nodes can be divided into 4 main groups: inferior maxillary, buccinator, infraorbital or nasolabial, and malar. These small lymph‐nodes are found in the subcutaneous plane, deep to the muscles, and alongside the course of the facial artery and vein. ²⁰

A facial process of the parotid gland or accessory parotid gland has been found in 21–69% of cadaveric cases. ²¹ An accessory parotid gland has the same echogenic features of the main parotid gland but it is not in contact with it. A facial process is an extension that exceeds the anterior border of the mandibular ramus and is continuous with the parotid gland (Figure 4). ²²

Figure 4.

Facial process of the parotid gland. A structure (arrows) with the same appearance as the parotid gland is seen between the subcutis and the masseter muscle, anteriorly to the parotid gland.

The cheek is supplied by branches of the external carotid artery, including the infraorbital, the transverse facial, and the facial arteries. A contribution also comes from a small branch of the ophthalmic artery, named the zygomaticofacial artery. To identify the infraorbital artery, as it emerges from the infraorbital foramen, the probe is placed in the transverse plane, slightly distal to the inferior eyelid (Figure 5). ²³ Other important structures traversing this region include buccal vessels, the facial artery, the transverse facial artery, and branches of the maxillary and mandibular nerves. ² , ²⁰ The transverse facial artery is identified as it originates from the superficial temporal artery in the preauricular region and courses through the parotid gland, as 1 or 2 branches. ² The facial nerve is observed as a small, tubular structure within the parotid gland, showing a hypoechoic middle and 2 ultrathin hyperechoic rims. ²³ , ²⁴ The probe is placed in the transverse plane just under the ear lobule, at the cranial level of the mandibular ramus. The masseter muscle is just below. The nerve should not be confused with the parotid duct that, however, emerges from the anterior border of the parotid gland and runs forward to end in the oral cavity.

Figure 5.

Transverse scan of the infraorbital region. Arrow points to the infraorbital artery passing through the bony foramen. MFP, malar fat pad.

Since the cheek is easily exposed to the sun radiation, a combination of modifications due to both chrono‐aging and photo‐aging will develop here. Ultrasound can demonstrate a number of these changes. ¹⁰ The subepidermal low echogenicity band (SLEB) is a hypoechoic band of variable thickness, developing between the epidermis and the dermis as a consequence of dermal elastosis (glycosaminoglycans deposits) (Figure 6). ² , ²⁵ The deep fat compartments of the cheek undergo hypotrophic changes while superficial fat compartments show hypertrophic changes and become ptosic. ¹ , ¹⁸ , ¹⁹

Figure 6.

Subepidermal low‐echogenicity band (SLEB). As a consequence of aging and of chronic sun exposure of the skin, a hypoechoic layer because visible between the thin hyperechoic line of the epidermis and the thicker, moderately hyperechoic line of the dermis.

A Cheek Lump: What to Do Next?

As in any other area of the body, a lump requires a systematic approach. ²⁶ Patient history must be collected accurately. Time from swelling appearance, any change in shape and size since the bump was first noted, current or previous presence of pain, general and local history (cancer, diabetes, immunodepression, drug consumption, travel in tropical countries, injury, surgery, cosmetic procedures, dental disorders), status of the cheek skin and mucosa. ²⁷ , ²⁸ , ²⁹ , ³⁰ Patient age and gender should always be kept in mind. Although benign lumps are by far more frequent than malignant ones, the need to rule out malignancy is always a key aspect. Ultrasound is commonly regarded as the first choice imaging modality in this clinical scenario. The examination will be carried out carefully, using B‐Mode and Doppler techniques. Changes in the patient pain and in abnormality appearance as the consequence of pressure applied through the probe are noted. Elastography and contrast agent injection are employed in selected cases.

Abnormalities arising from or within any of the anatomical structures described in the previous section may give rise to a palpable lump. Lesions may also spread to the cheek from the surrounding anatomical areas. Although in some cases the ultrasound findings are non‐specific, in many others there are some distinguishing features that, combined with patient history and physical examination, favor a specific diagnosis (Figures 7, 8, 9). The ultrasound features of the main cheek abnormalities are described in the next section.

Figure 7.

A–C, Cheek bump due to a mandibular carcinoma. A, Clinical photograph showing a cheek bulge (arrows). B, Ultrasound scan showing hypoechoic, heterogeneous mass (empty arrow), disrupting the hyperechoic jaw cortex (full arrows). C, Coronal, T2‐weighted MRI scan showing the mandibular mass (arrows).

Figure 8.

Adenomatoid odontogenic tumor of the jaw. Hypoechoic, heterogeneous lesion abutting from the bone cortex into the cheek soft tissue.

Figure 9.

Fibrosarcoma of the masseter muscle, transverse view. An inhomogeneous, lobulated, hypoechoic mass (arrows) is seen above the bony plane of the mandibular ramus.

Ultrasound Findings in Main Cheek Abnormalities

Inflammatory Abnormalities

Acne vulgaris is a chronic inflammatory condition, affecting the pilosebaceous unit of the hair follicles. Acne is quite common in adolescent subjects and the face represents the most common location. Acne may involve the dermis and hypodermis, beyond the possibilities of clinical examination. Ultrasound abnormalities consist of pseudocysts, folliculitis, fistulas, and calcinosis (Figure 10). ³¹ Post‐acne scars are quite common, with ice pick and boxcar scars being the deepest ones. ³² The sonographic scoring system categorized acne into mild (<5 pseudocysts without fistulas), moderate (5–9 pseudocysts without fistulas), and severe (>9 pseudocysts, with or without fistulas). ³¹

Figure 10.

A and B, Hypoechoic inflamed acne pseudocysts with edema of the fat below and with diffuse hyperemia. A, B‐Mode. B, Superb microvascular imaging.

Cellulitis involves the subcutaneous tissue. It generally appears hyperechoic due to the inflammatory change with interspersed hypoechoic regions attributed to oedema. ²⁰ Doppler scanning shows increased signals.

Orofacial infections are most commonly odontogenic in origin. The infection extends beyond the alveolar bone and spreads to the fascial spaces of the head and neck. ²⁰ Abscesses appear as anechoic collections or collections of mixed echogenicity. Strong perilesional flow signals combined with the complete absence of signals in the liquefactive center are typical (Figure 11).

Figure 11.

A and B, Cheek abscess. A, Clinical photograph showing a reddish bulge (arrow). B, Power‐Doppler scan demonstrating an ill‐defined, hypoechoic infiltration of the dermis and subcutis, with surrounding edema and diffuse hyperemia.

Idiopathic facial aseptic granuloma is a self‐healing inflammatory lesion. It usually presents as a well‐defined, dermal, oval, hypoechoic lesion, with the major axis parallel to the skin surface. During the active phase, surrounding tissues gain echogenicity. Increased flow signal can be detected at Doppler imaging, both peri‐ and intralesionally. ³³

Vascular Anomalies

Vascular anomalies are common congenital malformations of the vascular development and they frequently involve the head and neck region. The 2 broad groups include vascular malformations and benign vascular tumors, such as hemangioma. Among the locations of hemangioma in the skeletal muscles, masseter is one of the most common ones. Hemangioma appears as a complex mass of varying echotexture containing multiple cystic spaces. Posterior acoustic shadowing from intra‐lesional phleboliths may be observed. Doppler imaging may show slow internal flows (Figure 12). ³⁴ Lymphangiomas are especially common in the neck but the cheek region can be involved as well (Figure 13).

Figure 12.

A and B, Infantile hemangioma. Hyperechoic mass in the subcutaneous layer (A, arrows). Intense vascularization at superb microvascular imaging (B, arrows).

Figure 13.

Cystic lymphangioma of the cheek. A 3‐cm, multiloculated lesion (between calipers) is seen in the subcutaneous layer of the cheek, superficially and anteriorly to the masseter muscle.

Most Common Benign Tumors and Pseudotumors

Epidermal cysts are slow‐growing developmental lesions that arise from abnormally placed ectodermal tissue in the dermis or hypodermis. The cyst presents a granular layer and is filled with keratin. ²⁰ , ³⁴ Ultrasound allows the diagnosis of epidermal cyst and the demonstration of partial or complete rupture. Intact epidermoid cysts appear as round or oval avascular structures with well‐defined borders, posterior acoustic enhancement, and internal echoes (Figure 14). They are usually anchored to the dermal‐epidermal junction and occupy part of the subcutis. ³³ A connecting tract to the epidermal surface is identified in 20–30% of cases, corresponding to the punctum that may be seen at physical inspection. ³⁴ A ruptured cyst is less well‐defined with indistinct margins, partial or complete loss of dorsal enhancement, and increased peripheral flow signals. ²⁰

Figure 14.

A and B, Epidermal cysts. A, 4‐cm testis‐like cyst in the subcutaneous layer just above the parotid gland. B, Subcutaneous cyst in the midcheek.

Lipomas are composed of mature adipose tissue and represent the most common benign neoplasms in adulthood. About 13% of lipomas are located in the head and neck region, with the former being quite rare. ²⁰ Lipomas are usually seen in the subcutaneous layer or, less frequently, in the muscular layer. The cheek fat pads can be another possible site of origin for these tumors (Figure 15).

Figure 15.

A and B, Cheek lipoma. A, Transverse ultrasound scan showing a fatty tumor arising from the buccal fat pad, just anteriorly to the parotid gland. B, Contrast‐enhanced, axial T1‐weighted MRI scan confirming the fatty lesion (arrows).

Nodular hidradenoma is categorized into eccrine and apocrine. It presents as a slow‐growing, painless, mobile, and firm subcutaneous nodule. Ultrasound shows a lobulated, vascularized nodule with cystic components, septa, “snow fall” phenomenon, or fluid–fluid level (Figure 16). ³⁵

Figure 16.

Cheek nodular hidradenoma. Bilobated, cystic lesion with minor solid component and some flow signals at power‐Doppler imaging.

Pilomatricoma derives from the hair matrix and is especially encountered in the first 2 decades of life. Most common locations include the head, neck, or upper limbs. ³¹ Pilomatricoma presents as an asymptomatic, slowly growing firm and mobile nodule. In typical cases, ultrasound shows a hypoechoic rim, corresponding to the capsule, and a heterogeneous center, composed of nests of tumor cells. ³⁴ The location is in the subcutaneous layer, abutting the deeper dermis aspect. ³¹ The shape is round or oval and the border is regular or lobulated. Variable degrees of calcium deposits are quite common, particularly in the central aspect of pilomatricoma. Also, the amount of flow signals at Doppler imaging may vary (Figure 17).

Figure 17.

A and B, Cheek pilomatricoma in a child. A, Subcutaneous, partially calcified lesion in the subcutaneous layer. Note the intense back‐shadowing. B, The lesion is quite stiff at strain elastography.

Mucocele is a pseudocystic lesion that occurs due to the extravasation of mucus, often from an injured minor salivary gland or duct. Ultrasound shows a well‐defined, anechoic lesion, without flow signals. ²⁰

Nodular fasciitis is a rare benign tumor of uncertain origin arising within the deep subcutaneous layer, fascia, or within a muscle. Head and neck involvement is seen in 18% of cases. ²⁰ The clinical presentation is that of a rapidly growing, painful mass. The ultrasound appearance is not specific. lesions appear as isoechoic to hypoechoic nodules. Mild increase in vascularity is often identified.

Most Common Malignant Tumors

Malignancies arise from a number of structures, including the skin, lymph nodes, minor salivary gland or accessory parotid tissue, and other soft tissues of the cheek. The tumors can be primary or secondary in origin. Soft‐tissue lymphomas should also be considered, sometimes with a non‐nodular, panniculitis‐like appearance.

Skin malignancies can be categorized into melanomatous and non‐melanomatous. The latter group includes, first of all, squamous‐cell carcinoma and basal‐cell carcinoma but also other less frequent tumors, such as Merkel cell carcinoma, sebaceous carcinoma, eccrine porocarcinoma, and microcystic adnexal carcinoma, Kaposi sarcoma, and dermatofibrosarcoma protuberans. ³⁶ The face, being a sun‐exposed area, is one of the favorite locations of basal‐cell carcinoma. Also, the uncommon but aggressive Merkel‐cell carcinoma arises frequently in the head. ³⁷ In general terms, the ultrasound appearance of skin tumors is that of a hypoechoic thickening within the dermis, covered by a normal, ulcerated, or thickened epidermal line. The lesion can be homogeneous or heterogeneous, with well‐defined or ill‐defined borders. Basal‐cell carcinoma may show hyperechoic spots. Dorsal behavior may range from enhancement to attenuation. The vascularization degree may vary but usually there are several flow signals, especially at the deeper aspect (Figure 18). ³⁴ , ³⁶ Stiffness at elastography is usually high and heterogeneous.

Figure 18.

A and B, Local recurrence of a basal‐cell carcinoma. A, Clinical photograph showing a tiny, reddish speck (arrow). B, Split screen mode with B‐Mode and superb microvascular imaging showing an ill‐defined hypoechoic lesion, 3‐mm in width and 1‐mm in thickness.

Ultrasound may measure the width and thickness of the tumor, helping to choose the most appropriate treatment. Additionally, it is useful to plan the surgical excision by demonstrating the relation between the tumor and the critical structures below. ³⁸ , ³⁹ , ⁴⁰ Early detection of skin tumors recurrence allows a more conservative treatment, trying to achieve the oncologic radicality but, at the same time, limit the cosmetic effect in esthetic impact areas such as the face (Figure 19). ⁴¹ This is particularly the case of less aggressive tumors, such as basal‐cell carcinoma. ⁴² , ⁴³

Figure 19.

Satellite recurrence in a patient with history of cheek melanoma. Split‐mode screen with B‐mode and power‐Doppler. The new subcutaneous, 5‐mm nodule (between calipers) is hypoechoic, with ill‐defined borders and some flow signals.

Although more common in the major glands, salivary tumors can also arise in the minor salivary glands (hosted in the cheek mucosa) and ectopic salivary gland tissue (Figure 20). The most frequent tumors include the classical pleomorphic adenoma but also the monomorphic adenoma. The latter is usually partially cystic and may mimic malignancy. ²⁰

Figure 20.

Cystadenolymphoma (Warthin tumor) developing in an accessory parotid gland. Split‐screen, with B‐Mode and power‐Doppler. Oval, well‐defined nodule with multiple tiny fluid spaces.

Esthetics

Correction of an aged cheek, especially of the midcheek, is of great importance in rejuvenation procedures, to reduce wrinkles, improve facial contouring, and restore the features of youth. The most common esthetic injections include botulinum toxin, fillers, and deoxynucleic acid. Botulinum toxin blocks the neuromuscular junction, relaxing the muscles and eliminating the wrinkles. Exogenous fillers can be resorbable or permanent (hyaluronic acid, silicone, calcium hydroxyapatite, polyacrylamide, poly‐l‐lactic acid, etc.) and are injected in atrophic and/or concave regions to augment their volume and improve contouring (Figure 21). Particularly, fillers are injected into superficial fat compartments of the cheek. ⁴⁴ Deoxynucleic acid, unlike fillers, is employed to reduce fullness in areas of excessive fat accumulation. ¹⁴ , ²³ Fat grafting (lipofilling) is mainly used in the face to reduce facial wrinkles. ² Accidental injury to the cheek vessels and nerves may develop during any kind of injection. Pre‐procedural ultrasound allows mapping the critical structures. Intra‐procedural ultrasound may help inject into specific anatomical targets. Post‐procedural ultrasound will identify the filler, its location in skin tissues, and its extent after the cosmetic procedure and over time. Additionally, undesired effects and complications may be detected. Filler complications are categorized into immediate, early onset, and late onset. ² Aside from the vascular complications which are usually recognized during or immediately after the injection, other negative occurrences may be identified, such as the incorrect filler placement, filler migration, overfilling, abscesses, non‐inflammatory nodules, foreign‐body granulomas, delayed inflammatory changes, and fibrosis (Figure 22). ¹ , ² , ⁴⁴

Figure 21.

A and B, Fillers in the cheek. A, Silicone oil completely filling the cheek, with the classical hyperechoic, snowstorm appearance. B, Hyaluronic acid deposit in the deep cheek, with the cystic‐like appearance.

Figure 22.

A and B, Infraocular bump in a patient with cutaneous melanoma excision and subsequent filling of the scar defect with poly‐l‐lactic acid. A, Clinical photograph showing the scar (sky blue arrows) and the bump (yellow arrows). B, Transverse ultrasound scan at the infraocular level showing filler deposit and chronic inflammatory reaction with neocollagenogesis. The poly‐l‐lactic acid has migrated upward.

Ultrasound may help monitor the effect of anti‐aging skin products. ²⁵ , ⁴⁵ Particularly, thinning or vanishing of the SLEB is regarded as a sign of positive effect.

Thread lifting is used for minimally invasive face lifting. Threads can be classified into non‐degradable and degradable types. ² Threads should be inserted in the subcutaneous layer or SMAS layer along the natural tensor lines of the face, but considering the curved surface of the face, it can be difficult to perfectly locate the thread at the desired layer. ²¹ At ultrasound imaging, threads appear as thin bilaminar hyperechoic structures within the cutaneous layers, with some showing small thorns. ² A hypoechoic inflammatory and granulomatous tissue may surround the thread. Complications may develop during or after thread placement, including thread protrusion, dimpling, vascular damage (fistula, pseudoaneurysm, etc.), nerve injury, infection with abscess formation, parotid duct injury, and parotid gland perforation with chronic inflammation. ²¹ , ⁴⁶ Surgeons may modify the cheeks during the facelift. During this procedure, the skin of the cheeks is dissected and separated from the face. The underlying fat may be removed with liposuction.

In patients with scars (acne vulgaris, burns, traumatic injury, surgery, etc.) ultrasound can be employed to assess the thickness of the scar, to select the appropriate depth for laser resurfacing, and to assess the treatment outcome. ⁴⁷ , ⁴⁸ Ultrasound can help assess the degree of the engraftment of autologous adipose tissue graft during the surgical correction of scars by lipofilling. ⁴⁹

In candidates for bilateral removal of Bichat pad (bichectomy) to improve the esthetic of their face, a preliminary ultrasound evaluation allows assessing the volume of the fat pad. In many cases, the amount of fat is small and patients should be consequently discouraged from undergoing the surgical procedure. Ultrasound may also identify bichectomy complications ¹ , ⁵⁰ .

Miscellaneous

Enlargement of the lymph‐nodes in the buccinator group can present clinically as a cheek lump, painful or not. This is usually encountered in children while it is quite rare in adults. Causes include inflammation, infection, malignancy, and trauma.

IgG4‐related disease is an uncommon multisystem fibroinflammatory condition characterized by tumefactive lesions in various organs. Lesions that form plaques, nodules, or tumors. Abnormalities are hypoechoic with varying internal patterns and degrees of heterogeneity. Often patients also have elevated serum IgG4 levels. ⁵¹

Fistulae may open in the skin of the cheeks. Particularly, the path of extra‐oral, odontogenic sinus tracts may reach the skin. Ultrasound shows a hypoechoic nodular, triangular or “champignon shape” lesion in subcutaneous tissue, continuing with a slightly tortuous band‐like structure of variable length that reaches the cortical bone plate, which is focally interrupted. ⁵²

Parotid duct (Stensen duct) dilation may be due to stones, strictures, or tumors. ⁵³ The dilated duct may present as an elongated, transverse cheek swelling. In other cases it is the obstructing tumor (papilloma, carcinoma, etc.) to be present as a palpable cheek mass. In any case, ultrasound detects the overdistended duct and the obstructing abnormality (Figure 23).

Figure 23.

Parotid duct papilloma. Dilated duct proximally (empty arrows) and hypoechoic filling defect distally (solid arrow).

In patients with suspected facial nerve diseases, US may provide essential information about facial muscle status. This is the case of Bell palsy, post‐parotidectomy injury, tumors, myotonic dystrophy, and myasthenia gravis. Facial muscles on the palsy side become thinner and more echoic than the unaffected side, showing a decreased or absent active contractility. ⁵ , ⁵⁴

Ultrasound Guidance in Percutaneous Procedures

Ultrasound represents a useful tool to guide diagnostic and therapeutic percutaneous procedures in patients with cheek abnormalities. Given the real‐time, multiplanar approach, ultrasound may guide the percutaneous management of the abnormality whenever the clinical guidance is potentially regarded as less effective or risky. Small footprint probes, including hockey stick‐shaped transducers, are of special value, particularly when thin needles are employed. ⁵⁵

Ultrasound‐guided aspiration may be needed for patients showing fluid collections, including hematomas and post‐surgical seromas. Fine‐needle sampling can confirm the ultrasound suspect of abscess or tumor and can help establishing the infectious agent or the histological type, respectively. Pre‐surgical guidewires can be employed for lesions that are located deeply and/or that are close to vulnerable anatomical structures. Intraoperative ultrasound, however, is preferred, if available. There is a growing tendency, worldwide, to inject dermal fillers under ultrasound guidance. Before the procedure, ultrasound can be utilized to assess the presence, type, and amount of filler deposits from previous injection, to establish the anatomy and the variations (parotid gland facial process, accessory parotid gland, etc.), and to map vessels. In patients with excessive deposits of hyaluronic acid, injection of hyaluronidase under ultrasound guidance has proven more effective than under clinical guidance. Use of fewer units of hyaluronidase will be also possible is this case. The same applies to thread lifting, that is carried out in a safer why under ultrasound guidance. ²¹ Ultrasound helps to better target specific muscles responsible for fine lines, facial expressions, dystonia, hemifacial spasms, and spasticity and to inject them selectively with botulinum toxin. ¹⁴ , ⁵⁵ An ultrasound‐guided injection, especially important for the depressor anguli oris muscle but desirable also for the masseter muscle, decreases the risk of complications and improves the treatment effectiveness. ⁵⁶ , ⁵⁷ Ultrasound may also guide corticosteroids injection into filler‐induced granulomas. ¹

Finally, ultrasound may guide the accurate positioning of the electrodes within non‐palpable tumors for patients undergoing electrochemotherapy. ⁵⁵

Conclusion

The cheek is a complex anatomical area. Many abnormalities may develop herein, including inflammations, vascular changes, cysts, tumors, and esthetic complications. Ultrasound plays a key role in the assessment of cheek abnormalities and in guiding diagnostic and therapeutic percutaneous procedures. Appropriate knowledge of the examination technique, anatomy, and key findings is mandatory for an adequate ultrasound assessment.

Data Availability Statement

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.