Atypical Presentation of Lipoblastoma of a 9-Month-Old

Pediatric Otolaryngology Clinic

A 9-month-old female presented to the ENT clinic for a rapidly enlarging left neck mass over 3 months. The mass extends from the supraclavicular region to the occiput, involving the entire left neck. The patient exhibited weakness of the left upper extremity and no other symptoms. Magnetic resonance imaging (MRI) showed a well encapsulated, high-signal intensity mass with low-signal intensity septa on T1 sequence (Figure 1). On fat suppressed sequence, the corresponding mass demonstrated homogenous low signal intensity (Figure 2). Histologic analysis identified lobules of fat with occasional collections of lipoblasts and areas of myxoid degeneration. The mass was resected with no subsequent complications.

Figure 1.

Magnetic resonance imaging (MRI) of neck, coronal view of T1 sequence, which demonstrates a well-capsulated mass with high-signal intensity and low-signal intensity septa.

Figure 2.

Magnetic resonance imaging (MRI) of the neck, coronal view of fat suppressed sequence, which demonstrates homogenous low-signal intensity consistent with fat suppression.

Lipoblastoma is a rare benign neoplasm of fetal white fat cells presenting in different maturation stages within a mucopolysaccharide dominant myxoid matrix. ¹ It typically occurs in children under the age of 3 with predilection for the extremities and can rarely occur at other locations such as the head and neck, as seen in our patient. Males are 3 times more frequently affected than females. ^2,3 Patients typically present with a nontender enlarging mass of the soft tissue. ³ Symptoms can occur when there is a mass effect on structures like the mediastinum causing dyspnea and stridor. ²

Lesions indicating diffuse, infiltrative growth are characterized as lipoblastomatosis, whereas lipoblastomas are circumscribed. Differential diagnosis should include the more aggressive malignant myxoid liposarcoma to ensure no delay in excision if diagnosed. Imaging modality of choice to assist in diagnosis is T1-weighted MRI showing hyperintense signals. ⁴ Differentiating between the malignant liposarcoma and benign lipoblastoma can be made on light microscopy with consideration of patient’s age. Histopathology of lipoblastomas show a mixture of lipoblasts, stellate mesenchymal cells, and immature and mature adipocytes within lobulated tissues, as well as a plexiform capillary network, closely representing that of the myxoid variant of liposarcoma. ¹ As opposed to liposarcomas, lipoblastomas lack atypical mitoses, have an abundance of lipoblasts, and show lobularity. ⁵

If necessary, fluorescent in situ hybridization can confirm a DDIT3 gene rearrangement in liposarcomas. ⁵ It can also confirm a pleomorphic adenoma gene 1 (PLAG1) rearrangement in lipoblastoma 8q12 breakpoints located within PLAG1 intron 1. ¹ Immunohistochemically, liposarcomas are positive for MDM2 and CDK4, whereas lipoblastomas are negative. ³ Cytogenetically, lipoblastomas express clonal chromosomal rearrangements in the 8q11-13 region, leading to promoter swapping events occurring in PLAG1. Real-time polymerase chain reaction analyses reveal the entire PLAG1 coding sequence is fused with gene promoter regions of hyaluronic acid synthase 2 (HAS2) or collagen 1 α 2 (COL1A2). ¹

Management of lipoblastomas require complete excision of the tumor while preserving the vital organs in the process. Although there is a high recurrence rate with incomplete resections, it depends on the extent of resection. ⁵ If the tumor is completely resected, the prognosis is excellent. Chemotherapy is unnecessary in these patients. Postsurgery, a minimum of 5 years is essential for following up in order to identify any recurrences. ³