Clinical vignette:
63 year-old man presented for diabetes management. Physical examination
revealed a anterior 3-cm neck mass. Ultrasound showed a 3.1x1.4x2.7 cm
oval-shaped mass without internal vascularity and microcalcification
along the superior thyroid (Fig 1A). FNA showed red blood cells,
peripheral leukocytes with no thyroid follicular cells or colloid (Fig
1B). Neck MRI showed a 3.1-cm mass along the anterior aspect of the left
thyrohyoid muscle without intrinsic complex features and no abnormal
enhancement (Fig 2). A repeat FNA showed positive oil-red-O stain (Fig
3A). Because of the enlarging neck mass patient elected for surgery.
Histology demonstrated a fibrous capsule surrounding a homogenous
proliferation of adipocytes classic for a lipoma (Fig 3B).
Only 25% lipomas develop in the head or neck region. The FNA material
can easily be washed off the slide by alcohol during preparation which
is consistent with past reports describing histopathology of lipomas as
fat lobules with clear cytoplasm, scant cellular material and fibrous
material (1). One study demonstrated an overall sensitivity of 96% and
specificity of 98% in diagnosing soft tissue tumors by FNA (2). MRI is
an accurate way to confirm lipoma if suspicion is present.
This case highlights the anterior neck as an unusual location for a
lipoma often mistaken for a thyroid nodule as they typically are located
on the posterior or lateral neck as well as the accuracy of FNA in
diagnosing lipomatous tumors.