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Tumours in the brachial plexus are rare. Primary peripheral nerve sheath tumours (Schwannoma and Neurofibroma subtypes) are the most common and may cause neurological symptoms if they reach a critical size at anatomically narrow spaces. Lipomata may present at the level of the brachial plexus and although slow growing and soft tumours, they may produce neurological symptoms when they compress the brachial plexus. The symptoms are similar to thoracic outlet and compression may be in the interscalene triangle, retroclavicular or subpectoral spaces.
A Hibernoma is a rare lipoma subtype also known as an eosinophilic lipoma due to the classic histopathological appearance. The term Hibernoma comes from “hibernate” and the tumour is predominantly comprised of brown fat cells, abundant in hibernating mammals and in the adult human found in deposits around the spine, neck and axilla. The tumour is benign but rates of recurrence are high with incomplete excision.
Diagnosis is confirmed on biopsy and the decision to attempt excision is based on the presence of neurological symptoms, indicative of critical compression. As a slow growing tumour, neurological structures may accommodate and the anatomy may be distorted.
The surgery should be undertaken by a specialist familiar with brachial plexus anatomy and possible patho-anatomical variations. A clavicle osteotomy may be required when the tumour “dumb-bells”under the clavicle and the nerves are critically compressed. The tumours are vascular and dissection should proceed with care and meticulous haemostasis with ligation of feeding vessels.
INDICATIONS
The indications for excision are: Tumours that are increasing in size, causing pain, neurological symptoms and diagnostic uncertainty. MRI imaging and a biopsy should be performed and the results discussed in a soft tissue sarcoma MDT prior to planning surgical excision.
The tumour in this case had been present for many years and had increased in size with progressive neurological symptoms of pain, parasthesiae and subjective weakness. A biopsy confirmed a benign Hibernoma.
The imaging showed tumour extending from the superior apex of the posterior triangle to the anterior triangle abutting the lower pols of the thyroid and the carotid sheath. The scalenus anterior was encircled by tumour and the main mass traversed the plexus roots between the C6 and C7 components. Tumour extended in a retroclavicular direction to involve the subclavian vein and track around the plexus and brachial artery to the pectoralis minor.
SYMPTOMS & EXAMINATION
This case had grossly intact motor snd sensory function in the brachial plexus, however shoulder abduction and external rotation (ABER) with scapula retraction resulted in sensory disturbance to the hand and there was subjective weakness and fatigue with overhead activities. The tumour had increased in size and was extending from the posterior to anterior triangles of the neck and beneath the clavicle to the pectoralis minor. The tumour was soft and non-tender on palpation. There were reduced pulse volumes in the left wrist and a loss of the radial pulse on assuming the ABER provocation position. There were distended veins in the upper limb below the clavicle due to venous compression.
IMAGING
MRI confirms the extent of the tumour. The MRI should include the neck, thoracic outlet and the infraclavicular plexus region. MR angiography or Ct angiography may be helpful for surgical planning when there is compression and distortion of the neurovascular structures.
ALTERNATIVE OPERATIVE TREATMENT
Debulking is not to be advised as the rates of recurrence are high.
NON-OPERATIVE MANAGEMENT
A benign diagnosis on biopsy can lead to a conservative approach with serial clinical and radiological surveillance, particularly when the neurological symptoms are minor and there is no motor weakness and the potential risks of surgery outweigh the benefits of removal. In my experience many patients do eventually decide to pursue a surgical course and it is important to recognise neurological deterioration and increases in size as these factors can have a negative impact on the outcome following surgery.
CONTRAINDICATIONS
The main consideration is regarding appropriate informed consent and ensuring that patients are aware of the risks of a permanent neurological deficit or neuropathic pain following surgery. There is also the risk of complications following clavicle osteotomy including delayed union, non-union and metalwork loosening or prominence necessitating removal.
Patients should be consented for surgery including the risks of nerve injury, nerve pain, loss of supraclavicular nerve sensation, complications of the clavicle osteotomy and anatomical considerations due to the location including bleeding, chyle leak, palsy of XIth, long thoracic, phrenic or suprascapular nerves which are especially at risk.
A “Group and Save” should be sent for this patient as there is a risk of considerable bleeding due to the tumour vascularity and the site of surgery.
General anaesthesia with no neuromuscular paralysis to allow intra-operative nerve stimulation.
A brachial plexus set with malleable retractors, Mixter forceps, vascular instruments, a power driver and saw blade, a locking 3.5mm small fragment set with pre-contoured clavicle plates and templates (superior; antero-superior configurations).
Surgical sloops in a variety of colours for tagging nerves.
A nerve stimulator with the facility to control the stimulation threshold.
Monopolar diathermy plus epitome blade and bipolar diathermy.
Imaging may be required to confirm the position of the clavicle plate at the end of the procedure.
The patient is placed 30 degrees head up with a head ring and a narrow sandbag is placed under the medial scapular. When the clavicle osteotomy is performed this allows maximum opening at the osteotomy site.
The neck, ipsilateral upper hemithorax and whole upper limb are draped. This allows nerve stimulation intra-operatively with assessment of muscle contraction in the arm, forearm and hand.
I use adjunct paper tapes around the cloth drapes to prevent displacement during a long procedure.
The WHO checklist should be completed.
Antibiotics should be administered due to the planned clavicle osteotomy and fixation. Further doses as necessary to cover the length of the procedure.
The patient should be monitored for swelling and bleeding with regular observations including vascular observations of the operated limb.
Head up nursing reduces swelling.
A post operative haemaglobin should be measured at 24 hours if there was any significant intra-operative blood loss.
A chest and clavicle x-ray are useful post-operatively to confirm that the is no haemothorax / pneumothorax and the the clavicle fixation is satisfactory.
The drain can be removed at 24 hours if there is no significant bleeding.
I recommend continuing neuromodulator medications in the first 4-6 weeks post-operatively in patients taking them pre-operatively.
The local anaesthetic nerve block catheter can be removed at 48 hours if the patient has no significant pain.
The patient can be discharged at 48 hours and follow up assessment of the wound and the neurological function should be made in the outpatient department at 2 weeks.
Clavicle radiographs should be taken at 8 weeks to assess progress to wards union at the osteotomy site. Further x-rays are usually required at 4 months due to the typical slow healing of the osteotomy.
The motor and sensory function should be assessed and documented when the nerve block has worn off.
In this case there was post-operative weakness of the SSN (MRC grade 3 power) at 48 hours post operatively, improving to grade 4 at the two week assessment and full power (grade 5) at eight weeks.
There was transient paraesthesiae in the C6 territory with normalisation of sensation by two weeks.
There was sensory reduction inferior to the clavicle from sacrifice of the supraclavicular nerves. They were sectioned high in the supra-clavicular fossa to prevent excessive stretch injury during tumour mobilisation and irritation at the level of the clavicle fixation.
The pulses were immediately strong and maintained post-operatively with a warm hand and normalisation of the venous stasis.
The symptoms of ABER (abduction – external rotation) provoked paraesthesiae settled post-operatively.
A hibernoma is a slow-growing, benign tumour of brown fat. They are rare tumours and may occur in the limbs, neck, axilla or paraspinal regions. Patients are generally in their fourth or fifth decades. There is a female predominance. There are lipomatous and non-lipomatous sub-types. The non–lipomatous hibernoma may have one of three typical histological variants of which the eosinophilic variant is the most common. Differential diagnosis includes, atypical lipoma and liposarcoma. Biopsy is recommended prior to surgical resection.
Surgery is the recommended treatment for symptomatic hibernoma tumours. Displacement of anatomical structures by these slow-growing tumours renders them liable to injury and so resection in the brachial plexus should be in conjunction with surgeons experienced in brachial plexus surgery. The tumours are and adequate resection can usually be accomplished preserving vital structures.
References:
Miettinen MM, Fanburg-Smith JC, Mandahl N. Hibernoma. In: Fletcher CDM, Unni KK, Mertens F, editors.
WHO Classification of tumours Pathology and genetics of tumours of soft tissue and bone. Lyon (France): IARC Press; 2002. pp. 33–4
Furlong MA, Fanburg-Smith JC, Miettinen M.
The morphological spectrum of hibernoma. A clinicopathologic study of 120 cases. Am J Surg Pathol. 2001;25:809–14
Carinci F, Carls FP, Pelucchi S, et al.
Hibernoma of the neck. J Craniofac Surg. 2001;12:284–6
Ritchie DA, Aniq H, Davies AM, et al.
Hibernoma — correlation of histopathology and magnetic-resonance-imaging features in 10 cases. Skeletal Radiol. 2006;35:579–89
Reference
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