Background

Bednar tumor is a rare variant of dermatofibrosarcoma protuberans (DFSP) with an incidence of approximately 1–5% of all cases of DFSP [1]. It is a skin tumor of intermediate grade with limited potential for metastasis and high rate of recurrence. It occurs mainly in early adulthood or middle age, but cases are rarely reported in the pediatric population [1]. The diagnosis and management remain challenging in children. We report a case of a giant congenital Bednar tumor and discuss the surgical management and review of literature. We have adhered to the CARE guidelines while reporting this case.

Case presentation

A 2-year-old male child, presented with history of painless, pigmented, progressive, slow growing mass over the lumbosacral region since birth. There was no associated history of failure to thrive, fever, or trauma. The lower limbs movements were normal. There was no neurological deficit in bladder and bowel function. General physical examination was unremarkable. Local examination showed an exophytic firm to hard bosselated mass, 8 × 7 cm over the lumbosacral region. The mass was deeply pigmented and had hair growth over it (Fig. 1a). This lesion was freely mobile over the underlying muscles. There was no discharge or ulceration over the lesion. No regional lymphadenopathy could be appreciated. Two smaller superficial pigmented satellite skin patches (1 × 3 cm) were present over the back and thigh.

Fig. 1
figure 1

a Pigmented soft tissue tumor in the lumbosacral region. b Rotational flap cover over the tumor bed after complete excision

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Magnetic resonance imaging of the lesion revealed a heterogenous subcutaneous soft tissue sacral mass, likely soft tissue sarcoma (Fig. 2a, b). Fine needle aspiration cytology of the lesion was suggestive of pigmented variant of dermatofibrosarcoma protuberans.

Fig. 2
figure 2

a MRI- AxialT2 weighted sequence of the sacral region showing heterogenous predominantly exophytic mass located within the subcutaneous plane. b Sagittal T1 weighted sequence of the lumbosacral region in the paramedian plane showing the soft tissue mass

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Surgical excision was planned under general anaesthesia. The patient was placed in prone position. Complete tumor excision was done with a 2 cm clear margin. No macroscopic residual tumor was left behind. The large defect was closed with local rotation skin flap under mild tension. The other two lesions were excised in a second setting (Fig. 1b).

Cut surface of the tumor was dark drown, hairy, encapsulated, with firm to hard consistency. Histopathology of the lesion revealed spindle cells in storiform pattern which were pleomorphic. Melanin was present in most of the cell with 1–3 mitosis/10 hpf. Immuno-histochemistry was suggestive of spindle cells positive for CD34 and negative for CD68 and S-100. Margins were free of the tumor. The post-operative period was uneventful other than superficial wound dehiscence, which was managed by dressings alone. It healed successfully by secondary intention (Fig. 3). The patient is doing well for 2 years with no recurrence. Parental consent was availed for this research publication.

Fig. 3
figure 3

Follow up image after excision of the secondary lesion showing healed scar

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Discussion

In 1957, Bednar first described a group of nine cutaneous tumors that were characterized by indolent growth and a prominent storiform pattern, and in four cases by the presence of melanin pigment. He regarded these tumors as a variant of neurofibromas (storiform neurofibroma) [1]. Bednar tumor is a variant of DFSP containing abundant melanotic pigment. It is a disease of middle age third and fourth decade and is rarely described in children and even rarely in neonates (congenital variant) [2, 3]. Our case was peculiar, as the parents had noted the pigmentation since birth and was diagnosed as Bednar tumor at the time of presentation to the hospital.

They usually present as slow growing, pigmented lesion most frequently located in the trunk especially the back and shoulder. Morphologically as plaque like lesions of an erythematous-bluish or brownish color, with a smooth or irregular surface. The lesions are rarely exophytic like in our case and are nodular, multi-lobular, and of firm consistency. The tumor has a great potential for locally invasiveness and may reach the subcutaneous strata, fascia, and musculature, in a manner similar to that of DFSP making it prone for recurrence. Metastasis is rare and late and dissemination may occur via the hematogenous route and rarely lymphatic. The principle sites of metastasis are in the lungs, bones, liver, pancreas, stomach, intestine, thyroid, and brain.

The tumor needs to be differentiated from other pigmented lesions like fibrosarcoma, pigmented neurofibroma, melanotic schwannoma, desmoplastic (neurotrophic) melanoma. Bednar tumor is characterized histologically by scattered melanosome-containing dendritic cells in the background of spindle-shaped cells resembling fibroblasts arranged in a storiform pattern. Immunohistochemistry is confirmative for diagnosis [3]. Spindle-shaped tumor cells would be positive for CD34 and vimentin, but negative for S-100 protein and desmin; however, the pigmented cells would be positive for S-100 protein and negative for CD34 [3].

Surgical principle includes complete excision and clear base of the tumour. Most of the times it leaves a large defect requiring flap cover. Mohs’s micrographic surgery is the alternative treatment of choice, avoiding excessive excision in critical locations like head or hand; however, this may not be readily available [4, 5], leaving behind positive margins or base make the disease prone for recurrence. Wide local excision with 2 to 3 cm margin involving visibly uninvolved tissue may be difficult in infants and young children. We achieved a R0 resection with aggressive surgical excision and local rotational flap for coverage. A close follow-up to detect recurrences early is important [6]. Malignant transformation to fibrosarcoma with repeated recurrences may occur [7]. Since the lymph node metastasis is rare, lymph node dissection is not necessary.

We recommend a six monthly follow-up for at least 5 years after excision, even though reports of recurrence after two decades are available in literature.

Conclusions

Bednar is a rare and relatively less aggressive variant of DFSP, with intermediate grade malignant potential. It is uncommon in the pediatric population and rarely reported in the neonatal period and infancy. Complete surgical excision with wide local margins is curative. Local or vascularized flaps are usually required for managing large defects. Close clinical and radiological vigilance is recommended for early detection of local recurrence after surgical excision.