Teaching Case

A 72-year-old woman was admitted in the Emergency Department for X-ray film and ultrasound examination of the left hip for evaluation of a soft-tissue mass. On X-ray a large soft tissue mass was noted.

A 72-year-old woman came to ED for soft-tissue mass evaluation on her left hip (Fig. 1).
X-ray showed a large soft tissue mass, was followed by musculoskeletal US (Philips HD, head transducer L12-3), which revealed a mix type lesion of 7x7.5cm with internal echogenicity and microcalcifications (Fig. 2). Thereafter MRI was performed (Philips intera 1.5T) including the following imaging protocol: axial and coronal planes on T1W, T2W, STIR, gradient echo and post Gd T1 fat sat sequences.
MR images showed low signal intensity on T1W, high SI on T2 with scattered low signal micro-foci that might correspond to fibrous elements, keratin debris, microcalcifications. After Gd the mass showed peripheral irregular, patchy peripheral enhancement without solid nodules within the mass (Fig. 4, 4a, 4b).
The patient was led into the operating room for mass excision and the specimen sent for biopsy. Final diagnosis was large dermoid cyst.

Dermoid cyst is covered by a thick wall which contains sebaceous glands and all dermis adnexa. In addition hairs and large amounts of fatty masses originating from the ectoderm can be found. The rare malignant dermoid cyst develops squamous cell carcinoma in adults, in babies and children. [1] Dermoid cysts can be discovered as cutaneous cysts on the head, as cysts on the floor of the mouth or elsewhere in the head, or within the parotid gland, [2] or as cysts in the testes or penis. They can be large. [3] Radiography, CT and MRI usually allow the correct differential diagnosis of dermoid cysts.
Plain films are useful to exclude calcification or phleboliths so myositis ossificans and haemangioma can be excluded.
MRI is particularly helpful in diagnosing intracranial or intramedullary dermoid cysts and in assessing the dissemination of fatty masses or droplets. Surgical excision is the treatment of choice. If dermoid cysts are diagnosed early and treated with complete surgical excision, the prognosis is good, and no further complications are expected. Finally based on imaging features of the lesion we can exclude a number of soft tissue tumours to narrow the differential diagnosis.

The mass is low SI on T1Wi, so fat containing tumours (lipomas, liposarcomas), haemangioma haematoma and lesions containing melanin such as melanoma metastases can be excluded because they are high SI on T1Wi.
There are non haemosiderin deposits on gradient echo, therefore chronic haematomas and giant cell tumours (no longer called PVNS) can be excluded. [4]
On T2 Wi sequences the mass is high SI and contain only small spots of low signal intensity, making fibrous tumours less frequent.
After Gd enhancement the mass does not show nodules or thick enhancement only lineal peripheral enhancement making other cystic like tumours such as mixoids or mixoid liposarcoma type infrequent.
In conclusion low SI on T1, high SI on T2 with small hypointense foci and only peripheral rim enhancement makes dermoid cyst the most probably reliably diagnoses.[4]


In our case we followed the proper practice of imaging methods for performing surgery plan and for the best post-operative treatment.

US and MRI offer accurate information for the location and morphology of the skin cysts helping the surgeon to adequately plan surgery.