Primary spinal extradural lipoblastoma: Rare occurrence.

Dear Sir,

Tumors arising from adipocytes comprise around 6% of all soft tissue tumors. Of these around 94% are lipomas, 4.7% are lipoblastomas and 1.7% are liposarcomas.[1] Lipomas and lipoblastomas are benign tumors of mesenchymal origin in contrast to liposarcoma that is a malignant tumor. Atypical lipomatous lesion arising from embryonal fat cells is termed as lipoblastoma. Lipoblastomas are classified into two varieties: Lipoblastoma, which is well-encapsulated, well-circumscribed lesion, and lipoblastomatosis that is nonencapsulated, multicentric infiltrative tumor. It is a tumor of pediatric age group with a higher incidence in males. Lipoblastomas most commonly occur in extremities followed by trunk, abdomen and head and neck.[2] Jung et al. found a higher incidence in head and neck.[3] Spine and spinal cord involvement in lipoblastoma in most of the cases is secondary, and that may be from neck lesion, mediastinal lesion or from the pelvis and may result in neurological deficit. Though there are various reports of lipoblastoma with spinal extension, we have not found any case of primary spinal lipoblastoma.

A 1-year-old male child presented to us with delayed milestones, inability to move lower limbs since 6 months and difficulty in defecation and urination since 6 months. On examination, there was wasting of lower limb muscles. Tone in upper limbs was normal while there was hypotonia in both lower limbs. Power in lower limbs was grade 0; there was areflexia in both lower limbs and plantar reflex was absent. Furthermore, there was absence of sensation below the waist.

Magnetic resonance imaging (MRI) study of dorsolumbar spine revealed 8 cm × 4 cm size extradural lesion, which was isointense on T1 weighted image (T1WI) [Figure 1] and hyperintense on T2 weighted image (T2WI) extending from D8 to L2 vertebra with displacement of cord towards right side. Lesion was infiltrating the L2 vertebra and extending through the neural foramen into paravertebral space. The lesion was heterogeneously enhancing on gadolinium administration

Figure 1

T1WI axial cuts showing dumbbell shaped iso-intense lesion extending into left paraspinal space

Patient underwent D10 to L2 laminotomy in the prone position. Dura was intact. Extradural lesion was noticed which was yellowish, well encapsulated. It was soft to firm, minimally vascular and removed with microsurgical techniques. Part of lesion was eroding the pars interarticularis of L2 vertebra and extending into paraspinal space that was dissected out through same incision and excised. Dura was pulsatile at the end of surgery. Laminoplasty done.

Histopathological examination showed well circumscribed lesion composed of cells arranged in lobules separated by septae. It comprised of stellate mesenchymal cells and vacuolated lipoblast. The cells had abundant clear cytoplasm, and stroma was myxoid [Figure 2]. Patient was discharged on postoperative day 10 without any complication. However, there was no clinical improvement in lower limb power at 6 months follow-up.

Figure 2

HPR confirms lipoblastoma

Term lipoblastoma was proposed by Jaffe in 1926.[4] It is a tumor of pediatric age group with 55% of cases diagnosed before 1 year of age and almost all reported cases diagnosed in the first decade of life.[5] Occurrence of lipoblastoma in adults is rare. Male:Female incidence is 3.8:1.[6] Lipoblastomas most commonly occur in extremities (60%) followed by trunk (15%), abdomen (14%) and head and neck (14%).[2] However, Jung et al. found a higher incidence in head and neck.[3] Lipoblastomas show rearrangement in chromosome 8q11-13.[7] Rapid growth of lipoblastoma can give rise to compressive symptoms.

On radiological examination, lipoblastoma appears as nonspecific soft tissue mass without bone erosion.[7] MRI is an investigation of choice that classically shows high signal intensity on T1WI and T2WI identical to fat.[1] However, increased cellularity secondary to myxoid and mesenchymal component may lead to lower T1 weighted signals.[8]

Grossly size of lipoblastoma varies significantly. It is pale yellow lobulated lesion which is soft in consistency with moderate vascularity. Differential diagnosis includes lipoma, hibernoma, liposarcoma.[9] Lipoma is the closest differential of lipoblastoma and can be differentiated by presence of abundant vacuolation in cytoplasm.[10] In lipoblastoma, there is varying degree of cellular differentiation. Hibernoma is completely formed of brown fat with a central nucleus.[9] There is abundant finely granular cytoplasm. Apart from cellular atypia and hyperchromasia, liposarcoma can be differentiated by prominence of plexiform capillaries.[9] There is the absence of lobulation in liposarcoma.

Complete surgical excision is the treatment of choice in lipoblastoma. Incomplete resection is significantly associated with recurrence. Lipoblastoma arising from back and neck have a significant risk of recurrence.

In our case, there is primary involvement of the spine with spread to the para spinal region through eroded pars interarticularis giving rise to dumbbell configuration. The erosion of pars interarticularis secondary to mass effect and spread to para spinal region is uncommon in lipoblastoma. T1 weighted MRI showed decreased signal intensity which is unusual for tumor arising from adipocytes. This decreased signal intensity can be explained by occasional increased cellularity, that is, myxoid and mesenchymal components of lipoblastoma.

Lipoblastoma is rare benign tumor of adipocytes. Preoperative diagnosis may be difficult due to varying picture on imaging. Though benign lesion, it can cause dysfunction of the organ by its mass effect. It can erode the bone and can spread to adjacent planes. Complete excision of the tumor not only clinches the diagnosis but also prevent recurrence.