mercoledì 30 giugno 2010
Figure 1 and Figure 2 Axial contrast-enhanced CT demonstrates a thin-walled, well-defined hypodense lesion in the right sublingual space (Figure 1) which herniates posteriorly into the submandibular space (Figure 1). This lesion also tracks into the sublingual space lateral to the right genioglossus muscle (Figure 2). It is located anterior and lateral to the right internal and external carotid arteries and effaces the submandibular gland.
Diagnosis: Diving Ranula
A diving ranula is an extravasation pseudocyst of a simple ranula in the sublingual space rupturing out into the submandibular and or parapharyngeal space. It originates from trauma or inflammation of the sublingual gland or minor salivary glands in the sublingual space. With obstruction of the gland duct, the duct dilates and eventually ruptures, allowing its secretions to leak into the surrounding soft tissue.
CT is the imaging study of choice. On CT, the lesion demonstrates water content and thin walls with subtle or no wall enhancement. If the lesion is infected, it may show thick, enhancing walls. The characteristic shape is a collapsed cystic portion in the sublingual space - “tail sign,” with its head extending into the submandibular space. The sublingual spaces are located on the floor of the mouth on either side of the midline genioglossus muscles. They are separated from the submandibular space by the mylohyoid muscle that extends from the medial inferior aspect of the mandible to the hyoid bone. Thus, the sublingual space is superomedial to the mylohyoid muscle and the submandibular space is inferolateral to the muscle. Ultrasound and MR can also be used to characterize these lesions. Ultrasound demonstrates a well-defined hypoechoic mass in the sublingual and submandibular space. MR images show the lesion with signal intensity of water, though if infected, signal intensity can vary according to the protein content or presence of hemorrhage with some wall enhancement.
The differential diagnosis would include epidermoid or dermoid cyst, lymphangioma or cystic hygroma, abscess, submandibular gland cyst (mucocele), and second branchial cleft cyst. These lesions differ in appearance on CT.
The treatment of a diving ranula is removal of the ipsilateral sublingual gland via the cervical or intraoral approach. It is not necessary to excise the pseudocyst since it puts the surrounding structures at risk for damage. Biopsy can be done to confirm the diagnosis.