8.1 General Anatomy and Ultrasonographic Features

The epithelium of the floor of the mouth varies depending on the area one is studying. There are sections of keratinized and areas of nonkeratinized epithelium. The lateral area of the floor of the mouth contains fat tissue and the sublingual glands as well as other mucous secretion minor salivary glands [1–3].

When it comes to ultrasonographic evaluation of the floor of the mouth there are two ways to perform the exam. The basic and most frequently used way is superficially through the soft tissues of the neck which is done with a typical high-frequency linear transducer (ideally should be over 9 Hz) and the second more difficult to perform is with the use of intraoral probes [4–6]. This can either be done by covering the linear probes and inserting it into the mouth or with smaller “hockey sticks probes” that are easier for the space limitations the exam has.

The most frequently used landmarks in the floor of the mouth examinations are either the hard tissues of the area (mandibular ramus and hyoid bone) or the submandibular gland which helps orientate in soft tissues. The various layers of striated muscles are not easy to separate and identify, and in most cases they are just identified as muscle layers without specifying which ones they are. This is because the muscular layers are very thin and small as regions [3, 6].

The muscles of the tongue however with the use of ultrasound are seen as a whole and they appear homogenous with relatively high echogenicity. Upon examination, particularly in the extraoral ultrasonographic exam, it is important to examine the patient both with longitudinal and transverse views.

The easiest anatomical landmark in the floor of the mouth examination, is the curvature of the tongue’s surface. Also important is the determination of the air–tissue interface [3, 6].

Intraoral probes are more useful when we want to examine the tongues surface since they are easier to handle in such a small region.

Also, it is very important to study the entire length of the tongue which can be made by moving the probe beside the floor of the mouth as low as the hyoid bone. The muscles that need to be identified in the exam are the anterior belly of the digastric as well as the geniohyoid, mylohyoid, and genioglossus muscles, though they are not always so easy to identify.

8.2 Inflammatory Changes

Skin and soft tissue inflammatory lesions, including abscesses and cellulitides, are one of the most common problems seen by physicians. The soft tissue infections treatment varies depending on the depth of the infection or the presence of fluid which would require incision and drainage. The evaluation of skin and soft tissue infections can be very eaily performed with ultrasonography, enabling the examiner to diagnose an abscess cavity or deeper infection. The method of ultrasonography has been shown to be more reliable than clinical exam alone. The proper use of ultrasound allows for more appropriate patient care and management of their underlying infection. What is important when dealing with inflammatory changes is the differentiation between an abscess and a simple non developed inflammation.

Simple inflammatory lesions are not clearly delineated and their borders are diffused and hypoechoic. They often appear without clear borders and blurred (Figs. 8.1, 8.2 and 8.3).

Abscesses, on the contrary, have clear borders; they are also hypoechoic lesions and they may have an anechoic central area with acoustic enhancement, or areas of perfusion of the tissue areas (Figs. 8.4, 8.5 and 8.6).

Like all inflammatory lesions there is high vascularity and often swelling of the region involved. Thus as in all inflammations the correlation to the clinical status of the lesion is very important.

8.2.1 Ranulas

Ranulas are a type of mucous cyst, which is characteristic to the floor of the mouth unilaterally [7].

It is included in the inflammatory lesions of the floor of the mouth since it is according to most authors the result of injury of the secretory duct of the sublingual gland, which in many cases is common to the duct of the submandibular gland while in fewer cases it is from the ducts of minor sublingual glands [8, 9].

A special case of ranula is the diving or plunging ranula, which is considered to appear from a gap between the mylohyoid muscle in which a part of the sublingual gland descends. This leads to the distribution of the saliva through the mylohyoid muscle to the floor of the mouth and submandibular area [10–16].

Clinically, it appears as a semicircular swelling between 1 and 3 cm which is palpating and is located unilaterally in the floor of the mouth. Sometimes when large in size it may force the tongue away from its normal position and cause difficulties in speech, swallowing, and chewing. As with mucous retention cysts, ranulas may burst and reappear at different time frames.

The clinical diagnosis is set from the position and the characteristic image of the lesion [15].

The key to the radiological identification of ranulas is the characterization of the connection to the sublingual space [9–16].

With the use of ultrasound ranulas usually appear are clear hypoechoic lesions, similar to cysts with thin walls [11–13]. Sometimes when infected they may contain fine internal echoes, usually due to the presence of debris from previous episodes of inflammation [14]. A ranula usually appears as a unilocular, well-defined, cystic lesion in the submental region deep to the mylohyoid muscle. For a diving ranula, the bulk of the cystic collection is in the submandibular region, but a small beak may be seen within the sublingual space [12–16]. (Figs. 8.7, 8.8 and 8.9).