Differential diagnoses include atypical lipomatous tumour/well-differentiated liposarcoma, pleomorphic lipoma, neurofibroma, nuchal fibroma, lipoblastoma, hibernoma, cellular angiofibroma [13
], extramammary myofibroblastoma, and solitary fibrous tumour.
It is important to note that reactivity to CD34 immuno-histochemical stain is not specific to only spindle cell lipoma as other entities can demonstrate immunoreactivity to CD34 such as atypical lipomatous neoplasm (ALN)/well-differentiated liposarcoma (WDL).
ALN/WDL is the most common form of liposarcoma seen in late adult life with equal gender affectation generally. They contain a significant component of mature fat and tend to have less well-defined borders than lipomas [14
]. The favoured sites for ALN/WDL are deep soft tissues of extremities and retroperitoneum compared to SCL that favour the subcutis of the posterior neck, back and shoulders.
SCL shows cytogenetic aberrations—mostly loss of 16q material and less frequently material from 13q. This coupled with the usual absence of giant marker and ring chromosomes that are typically seen in atypical lipomatous tumour/well-differentiated liposarcoma supports their distinction.
Immunostaining for MDM2 and CDK4 has been shown to be a relatively sensitive and specific means of identifying and separating atypical lipomatous neoplasm/well-differentiated liposarcoma from various benign lipomatous lesions [15
In this case report, histologic findings did not demonstrate sufficient nuclear atypia to suggest a diagnosis of atypical lipomatous tumour and further immuno-histochemical markers that would make such a diagnosis possible (CDK4, p16) were found to be negative.
SCL shares overlapping clinical, morphologic, and immuno-histochemical findings with pleomorphic lipoma as well as the same cytogenetic aberrations. The differential diagnosis of SCL or pleomorphic lipoma depends on which elements predominate [14
Dermatofibrosarcoma protuberans (DFSP) is also a differential of SCL. It however typically arises in the dermis, often in younger patients and lacks the characteristic ropey collagen of SCL [14
Schwannoma and neurofibroma have a similar striking nuclear palisading and conspicuous mast cell infiltrate present in some SCL. These however invariably express S-100 protein which is negative in SCL [14
SCL may also be mistaken for several sarcomas, including myxoid liposarcoma or spindle cell liposarcoma. SCL is however more circumscribed, lacks lipoblasts, with characteristic ropey collagen bundles. The presence of multinucleated floret-like giant cells is characteristic of pleomorphic lipoma and is occasionally seen in atypical lipomatous tumour/well-differentiated liposarcoma.
In this case report, the spindle cell lipoma presented a diagnostic and management dilemma as it could not be clinically differentiated from a liposarcoma which would require a more radical approach to treatment. The radiologic findings of a complex internal architecture with fine septations allowed differentiation of the preoperative differential diagnosis from a benign lipoma or possible malignancy but could not differentiate between a liposarcoma or a spindle cell lipoma.
The authors suggest that when radiologic findings suggest a complex internal architecture suspicious for a diagnosis of a possible lipomatous tumour, it is imperative to obtain a biopsy prior to definitive surgery. Histologic interpretation is crucial and this can be supported by the use of immune-histochemical stains. Immuno-histochemical stains demonstrating positivity for CD34 can be helpful in diagnosis of CD34 positive tumours such as spindle cell lipoma, and the differential diagnoses discussed such as atypical lipomatous tumour and dermatofibrosarcoma protuberans (DFSP). As discussed, further differentiation can be made based on clinical presentation, immunoreactivity for actin or desmin, S-100 protein staining of mature lipocytes, the presence/absence of ropey collagen bundles, multinucleated floret-like giant cells and cytogenetic aberrations. In difficult cases, fluorescence in situ hybridization (FISH) analysis can be helpful.
A preoperative diagnosis of spindle cell lipoma is crucial to surgical management as it impacts on the consent process, surgical approach, extent of surgery, and management.
In making a preoperative diagnosis, tissue sampling is required with either FNA or core biopsy. However, it is important to note that FNA may be nondiagnostic as it was in this case, because the specimen consisted largely of fatty cells. Core biopsy is preferable and can be obtained by an initial procedure under anaesthesia prior to definitive surgery based on a histological diagnosis. A preoperative diagnosis will guide the consent process as such patients can be warned of the risks of neurovascular injury as well as determining the extent of surgery.