CASE 17798 Published on 05.07.2022

A rare case of ankle soft tissue sarcoma: 'Creeping beneath the skin'

Section

Musculoskeletal system

Case Type

Clinical Cases

Authors

Dr Subramanian V., Dr Jenikar paul, Dr Nikhil Ravooru, Dr Archana Bala, Dr Sai Shankar, Dr Harshavardhan B.

Shri Sathya Sai Medical College and Research Institute, India.

Patient

63 years, female

Categories
Area of Interest Anatomy, Extremities, Musculoskeletal soft tissue ; Imaging Technique CT-Angiography, MR-Angiography, MR-Diffusion/Perfusion
Clinical History

A 63-year-old female patient presented with a swelling over the right ankle for 1 year, slowly growing in size. History of a surgery over the right ankle for similar complaints. No other comorbidities.

Imaging Findings

Plain anteroposterior & lateral radiograph showed an ill-defined soft tissue lesion in the posteromedial aspect of the right ankle.

Ultrasonography with colour doppler study showed an ill-defined heteroechoic lesion with significant internal vascularity.

Non-contrast computed tomography (NCCT)  showed a well-defined lobulated isodense lesion measuring ~ 5.3 x 3.5 x 1.7 cm (CC X AP X TR) in the subcutaneous plane of the posteromedial aspect of the right ankle extending from the level of the distal metaphysis of tibia up to the level of tibiotalar joint approximately 3.5 cm above the Achilles tendon insertion site. There was no evidence of calcification/haemorrhage seen within the lesion. Adjacent bones appeared normal.

MRI (with contrast) showed the lesion to be isointense on T1WI & hyperintense on T2WI/STIR sequences. Few areas of flow voids were noted within the lesion on T2WI. The lesion showed true diffusion restriction with no evidence of gradient blooming. Surrounding subcutaneous tissue showed diffuse edematous changes. Post-contrast imaging showed significant heterogeneous enhancement within the lesion. There was no obvious infiltration into the overlying skin but infiltration of the subcutaneous fat tissue was noted.

Discussion

A. Background

Dermatofibrosarcoma protuberans (DFSP) is a rare, low-grade, locally aggressive neoplasm, accounting for approximately 6% of soft tissue sarcomas. DFSP is classified as a fibroblastic/myofibroblastic tumour. [1] Histologically, DFSP is composed of uniform spindle cells with elongated nuclei arranged in an interwoven fascicular storiform or cartwheel pattern, embedded in varying amounts of collagen. Immunohistochemically, CD34 is positive in 90% of DFSP patients. [9]  

B. Clinical perspective

DFSP is more common in adults between 20 and 50 years. [1] There is no sex bias. [2] DFSP can occur in almost any part of the body, the most common site is the trunk, followed by proximal extremities; head and neck are less common.[1,2] DFSP grows slowly, ranging from several months to many years. [1] DSFP often demonstrates round, oval, or irregular soft tissue mass, and protrudes skin surfaces to different degrees. The tumour is usually solitary and relapsed cases often show lobulated or multiple nodules. 

C. Imaging Perspective

On ultrasound, DFSP appears as a low echo mass with a rich blood supply. [3, 4] On CT, DFSP appears as a solitary, well-defined isodense cutaneous or subcutaneous mass, with no calcification. DFSP shows homogeneous enhancement for small tumours and nonhomogeneous enhancement for large tumours. [5–7].

On MRI, the tumour appears as a well-defined isointense mass compared with muscle on T1-weighted images and hyperintense on T2-weighted images. On contrast-enhanced T1-weighted images, the tumour demonstrates intermediate or marked homogeneous or heterogeneous enhancement. [3, 8-9] DFSP is often rich in blood supply. [4, 5] 

In the report by Garg et al [5], a DFSP arising in the leg showed contiguous infiltration of the underlying bone. In another report by Thornton et al,[8] the proposed surgical margins were enlarged relying on the MR imaging findings in 2 out of 5 cases. Presurgical MRI is important for surgical plans and follow-up.

D. Outcome

The prognosis of DFSP is generally good. Surgical resection is the main treatment for DFSP. However, DFSP has a high rate of local recurrence, but little distant metastasis. [5] Postoperative follow-up is particularly important, especially in the first 3 years. [11] 

E. Take-home message

DFSP is characterized by a subcutaneous well-defined soft tissue nodule or mass on plain CT/MR scans and shows intermediate-to-marked enhancement on contrast-enhanced CT/MR scans. The imaging findings for DFSP are nonspecific, but the diagnosis can be made in an appropriate clinical setting.  

Differential Diagnosis List
Dermatofibrosarcoma protuberans over the posteromedial aspect of the right ankle
Lipoma: Fat density on CT, and hyperintense on T1- and T2-WI.
Liposarcoma: Inhomogeneous attenuation containing soft tissue & calcification within the fatty mass, and with invasion/infiltration of adjacent structures.
Dermatofibroma: Occurs in limbs, accompanied by thickening of the skin tissue.[12]
Neurogenic tumours include schwannomas and neurofibromas: Schwannoma often shows cystic degeneration & heterogeneous enhancement.
Hemangioma: Phleboliths on CT, isointense on T1-WI, and hyperintense on T2-WI.
Final Diagnosis
Dermatofibrosarcoma protuberans over the posteromedial aspect of the right ankle
Case information
URL: https://www.eurorad.org/case/17798
DOI: 10.35100/eurorad/case.17798
ISSN: 1563-4086
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