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| Discussion |
Case Report: A 38-year-old man presented with a history of gradually increasing swelling in the neck associated with difficulty in swallowing. The swelling had gradually increased over a period of three months. On examination, the swelling was approximately 3 x 4 cms in size; rounded , well-defined, freely mobile & moved with swallowing. It was soft & compressible.
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Fig. 1 |
Fig. 2 |
Coronal & axial CT scan showing a well circumscribed, hypodense mass lesion,,with a subtle fat-fluid level is seen in the sublingual space. The mass displaces the mylohyoid muscle laterally causing mass effect on the oropharynx.
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Fig. 3 |
T2 Fat-suppressed coronal image showing a well-circumscribed hyperintense lesion in the sublingual space causing mass effect on intrinsic muscles of tongue.
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Fig. 4 |
T1 sagittal image showing hyperintense soft tissue lesion suggestive of fat in sublingual space .
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Fig. 5 |
Fig. 6 |
T1 axial & T2 axial images showing mass effect & displacement of the submandibular gland posteriorly. Note the normal submandibular gland on right side & the mass effect on the oropharynx.
Diagnosis:
Sublingual Dermoid cyst
DISCUSSION:
Dermoid cysts are the least common of congenital neck lesions accounting for only 7% of all cysts in this location. They are derived from epithelial cell rests that get embedded in the midline during embryologic closure of the first & second brachial arches. In the oral cavity, the most common location is the floor of mouth i,e. sublingual, submandibular or submental regions. Localization of the cyst by imaging is necessary to define the relation to the mylohyoid for appropriate surgical approach. These lesions can occur either in the midline or slightly off the midline.
On CT imaging , they typically appear as well-defined, low attenuation, thin walled unilocular cysts .The wall of the cyst enhances following contrast administration.
On MRI, they show a heterogeneous signal intensity on T1 weighted images & appear bright on T2 weighted images. Simple dermoid cysts may be impossible to distinguish on the basis of imaging alone from other common cystic lesions located in this region such as epidermoid , lymphangioma & ranula .
Compound dermoid cysts have a variable appearance depending on their fat content .On CT they may appear filled with homogeneous low attenuation ( 0 to 18 HU ) material or the central cavity may demonstrate a fat-fluid level or a single fat globule . Multiple low attenuation nodules due to coalescence of fat globules give a typical “sack of marbles” appearance and, when present, is considered to be virtually pathognomonic of this condition.
The surgical approach for lesions located superior to mylohyoid i,e., in floor of the mouth is intra- oral whereas that for lesions inferior to mylohyoid muscle i,e., in the neck is external. The advantages of an intra oral approach are a shorter recovery time, absence of a conspicuous scar & the mylohyoid muscle can be preserved.