Neuroradiology Case of the Week

Case 25

Manoj Ketkar, MD, Larry Buadu, MD, PhD, S. Ekholm, MD, PhD,
and P-L Westesson, MD, PhD, DDS

Clinical Presentation: A 24-year-old male presented with a lump under his tongue for two months. There was clinical suspicion of tumor in the floor of the mouth.

Radiological Findings: A well-defined oval mass lesion is noted in the floor of the mouth on the right side. This mass is hypo-intense to the muscles on T1-weighted images and is hyper on T2-weighted images (Fig. 1 A & B). On the contrast enhanced images there is peripheral enhancement of the lesion although the main portion of the lesion did not enhance (Fig. 2). A dilated Wharton’s duct was noted on the right side with a dilated hilum in the region of the right submandibular gland.
   A smaller intraosseous lesion is noted on the left side. It is has signal characteristics similar to the lesion on the right side in the floor of the mouth but the left one is in the bone of the mandible. It is a radicular cyst on the left side.

Figure 1A	Figure 1B
Figure 1 A & B: Axial T2-weighted and T1-weighted images reveal an oval mass on the right side of the floor of the mouth and an intraosseous mass on left side of the body of the mandible. Also noted the dilated Wharton’s duct on the right side (arrow).
Figure. 2: A coronal post gadolinium image demonstrates no enhancement within the right floor of mouth mass. The periphery of the lesion is enhancing. This is probably due to inflammation/infection with capsular hyperemia.

Diagnosis:  Ranula on the right side with left-sided intraosseous cyst; radicular cyst.

Discussion:
   A ranula refers to a mucous retention cyst that occurs primarily in the sublingual gland. It occurs in two forms, a simple ranula and a deep or plunging ranula. A simple ranula, which is the most common form, is a retention cyst that remains in the floor of the mouth (sub lingual space) above the level of mylohyoid muscle. The second type of ranula, which is a deep or plunging ranula is a mucocele that develops from rupture of the wall of a simple ranula. It often penetrates to the submandibular space, which is below the mylohyoid muscle.
   The differential diagnosis for simple ranula includes a lateral dermoid or epidermoid cyst, lipoma and salivary gland tumor [1]. Ranulas are most commonly result from trauma or obstruction of sublingual salivary gland or its ductal elements.
   On CT, the simple ranula is usually an ovoid shaped cyst with homogeneous center attenuation region of 10-20 HU. The cyst wall is either very thin or not seen. On MR imaging, simple ranulas are typically low on T1-weighted images and high on T2-weighted images, reflecting its high water content. The treatment of choice for ranulas is, of course, surgery.

References:

1. Som PM and Curtain HD (Eds.). Head and Neck Imaging. (4th Ed.) Mosby, St. Louis, MO, 2003, pp. 2063-2066.