Case report
A 16 year old female was incidentally found to have mediastinal widening
in plain chest X-ray took at medical check-up and referred to thoracic
surgery department of Seoul National University Hospital (SNUH) at
2019-04-10. She denied any underlying diseases or family history of
malignancy, and she had never experienced smoking or alcohol. She had
dysphagia, weight loss and exertional dyspnea at the time of the first
visit, but her symptom was not severe and neglected until plain chest
X-ray was taken. Her initial height was 160cm and body weight was
42.5kg.
Chest CT taken at outside hospital showed about 9.5x6.1cm sized fat
containing mass lesion without calcification in the lower neck to
posterior upper mediastinum, and tracheal compression was observed. The
differential diagnosis made by radiologist was well differentiated
liposarcoma or immature teratoma. F-18 FDG PET/CT was taken and it
showed mild uptake (~1.9) at aforementioned mass, with
metabolic defect in fat portion (Figure 1). The core needle biopsy of
the mass was done, and the pathologic report confirmed lipogenic tumor
with some brown fat cells, suggestive of hibernoma.
Mediastinal mass excision via full sternotomy under V-V ECMO support was
done by thoracic surgery team. Anesthesiologist recommended V-V ECMO
support because there was mid tracheal compression more than 50%, with
diameter lower than 5mm, through which plain E-tube ID 3.0mm could
barely pass. Before the anesthesia induction, fiberoptic, rigid
bronchoscope was prepared and high flow nasal cannula was applied for
the possibility of emergent airway collapse. Under MAC anesthesia, the
V-V ECMO was inserted with 17Fr catheter at right and left femoral vein,
then the general anesthesia with endotracheal intubation with plain ID
6.5mm tube was followed. There was no difficulty during the intubation
process, and the intubation depth was 22cm. Airway patency was checked
with fiberoptic bronschoscope.
During the main procedure, approach through full median sternotomy was
made, and large mass through superior aspect of anterior mediastinum to
anterior neck was identified. The mass was well circumscribed and
lobulated, and the adhesion to nearby tissues was minimal. There was no
evidence of vessel, nerve, pleural invasion, and delicate dissection
with complete removal was performed. Bilateral recurrent laryngeal
nerves were identified and preserved. The patient was transferred to
pediatric intensive care unit after the surgery, and was discharged at
postoperative day 5 without any complication.
The size of the mediastinal mass was 9.6 x 7.9 x 3.8cm, and the final
pathology confirmed mediastinal hibernoma. On gross examination,
resected mediastinal lesion contained fatty tissue-like yellowish mass
measuring 5.3 cm. The mass was composed of polygonal cells resembling
brown fat with multivacuolated cytoplasm, admixed with mature
adipocytes. The lesion was also characterized by fibrous septae and
myxoid stroma, suggestive of myxoid variant. Small, delicate, branching
capillaries were noted. Nuclei were small with no significant atypia,
and necrosis was not observed. Immunohistochemistry for CD31 showed
staining in hibernoma cells as well as capillary endothelial cells
(Figure 2).
Regular follow up at outpatient clinic was done with chest PA, and there
was no evidence of recurrence. Initial symptoms such as dysphagia and
dyspnea were also disappeared, and she had no complaint. She also gained
weight, and her body weight was 47.4kg at 2022-01-10. However, the chest
CT taken at 2020-08-26 showed small attenuating lesion at left
supraclavicular area. The size of the mass was increased to about 2.2cm,
which was suspicious for residual mass or recurrence of hibernoma. Due
to its location, the patient was referred to Otolaryngology department
at SNUH.
2022-01-10 neck CT was taken, and the size of the left level VI mass was
increased (2.2 -> 2.6cm) (Figure 3). In addition, 1.6cm
mass was incidentally identified at right submandibular gland posterior
aspect, and followed ultrasound gun biopsy confirmed pleomorphic
adenoma.
Eventually, left level VI neck dissection with right submandibular gland
mass excision was done at 2022-01-25. Electromyography tube was
intubated for intraoperative recurrent laryngeal nerve monitoring. About
5cm midline horizontal incision was made along the skin crease at the
level of thyroid gland. During the removal process, the mass was well
circumscribed with capsule and pinpoint capsule violation was observed,
but there was no definite spillage of tumor content. Delicate dissection
was performed to save nearby structures (Figure 4). Eventually, complete
removal was achieved, and left vagus nerve, carotid vessels, thyroid
gland were saved. Left recurrent laryngeal nerve was not identified due
to severe adhesion, but the patient’s vocal fold movement was intact
postoperatively. Suspicious fat tissue nearby main mass was also
removed. The right submandibular gland mass was also removed in a
routine manner.
The recurred tumor at left level VI was also confirmed as hibernoma,
which had similar histologic features with more pronounced myxoid stroma
compared to mediastinal mass (Figure 2). Removed fat tissue adjacent to
main mass was diagnosed as mature adipose tissue. The right
submandibular gland was confirmed as pleomorphic adenoma with clear
resection margin.
The patient was discharged at postoperative day 2 without any
complications, including vocal fold palsy, hematoma, wound infection,
etc. There was no evidence of recurrence at 6 month follow up neck CT.