Ranulas

• Thin-walled cystic lesion in the floor of the mouth above the mylohyoid muscle (simple ranula) or extending below it into the submandibular space (plunging ranula)
• Characteristic 'tail sign': thin tail or fluid collection connecting the cyst to the sublingual space, key to diagnosis especially when large and distant from origin
• T1 low signal, T2 high signal on MRI indicating simple fluid with possible enhancement of the thin wall on T1 post-gadolinium

• CT shows thin-walled cystic lesions with central fluid attenuation of 10-20 HU in uncomplicated cases.
• MRI demonstrates T1 low signal and T2 high signal intensity consistent with simple fluid content, with possible thin wall enhancement on T1 post-gadolinium best seen with fat saturation.
• The 'tail sign' is the pathognomonic imaging finding: identification of a connection to the sublingual space, which may appear as a thin tail or significant fluid collection, essential for diagnosis when ranulas are large and have dissected away from their origin.
• Simple ranulas are confined to the sublingual space above the mylohyoid muscle, while plunging (diving/cervical) ranulas extend through or around the mylohyoid muscle into the submandibular space with a collapsed sublingual portion.
• Uncomplicated ranulas appear as thin-walled, unilocular, homogeneous cystic lesions; if infected or previously intervened, walls become thicker and fluid attenuation increases, with surrounding fat stranding if acute infection present.
• On ultrasound, uncomplicated ranulas appear as thin-walled cystic lesions visible on both transcutaneous and transoral approaches; infected ranulas show thicker walls and more echogenic fluid content.
• Most ranulas are pseudocysts without true epithelial lining, instead lined by condensed connective tissue response to inflammatory salivary secretions.
• Sialography of the submandibular duct typically shows no communication with the cyst, confirming the ranula is not a simple ductal obstruction.

• Cystic hygroma: typically occurs in infants and differs in age of presentation and anatomic distribution pattern.
• Thyroglossal duct cyst: usually located in the midline, whereas ranulas are in the floor of mouth off midline.
• Second branchial cleft cyst: typically located at the anterior border of the sternocleidomastoid muscle rather than the floor of the mouth.
• Dermoid/epidermoid cyst: lacks the characteristic sublingual space connection and 'tail sign' that identifies ranulas.
• Cervical abscess: distinguished by thicker walls, surrounding fat stranding, and possible clinical signs of infection; ranulas have thin walls unless infected.
• Dilated submandibular duct or sialolithiasis: the 'tail sign' connection to sublingual space and lack of communication on sialography distinguish ranulas from primary ductal pathology.

When reporting a ranula, specifically identify the presence of the 'tail sign'—the connection to the sublingual space—as this is the pathognomonic feature that distinguishes ranula from other floor-of-mouth cystic lesions, then classify as simple (above mylohyoid) or plunging (below mylohyoid), note the cyst wall thickness and fluid characteristics (thin-walled and homogeneous if uncomplicated, or thick-walled with surrounding stranding if infected), and describe any mass effect on adjacent structures.

• Mistaking a large, dissected ranula for a primary submandibular or cervical cyst by failing to identify the connecting 'tail sign' to the sublingual space.
• Confusing an infected or previously treated ranula with an abscess; infected ranulas show thicker walls and increased attenuation/echogenicity but lack the full picture of acute infection unless superimposed.
• Misdiagnosing plunging ranulas as primary submandibular space lesions when the collapsed sublingual portion and connection are not carefully evaluated on all imaging planes.
• Overlooking the importance of complete sublingual gland excision in surgical planning, leading to patient discussion about high recurrence risk (70-85%) if only cyst drainage or partial excision is performed.