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| Year : 2001 | Volume
: 49
| Issue : 2 | Page : 194-6 |
Solitary skull metastasis from mucoepidermoid mimicking a parotid tumour.
Sousa J, Sharma RR, Pawar SJ, Mahapatra A, Mishra GP
Department of Neurosurgery, The National Neurosurgical Centre, Khoula Hospital, Post Box-90, Postal Code - 116, Mina-Al-Fahal, Muscat, Oman.
Correspondence Address:
Department of Neurosurgery, The National Neurosurgical Centre, Khoula Hospital, Post Box-90, Postal Code - 116, Mina-Al-Fahal, Muscat, Oman.
Metastatic parotid tumours in the skull are very rare. An interesting case of a mucoepidermoid parotid tumour metastasizing to the skull vault is described in a patient who had previously been operated for a pituitary adenoma 20 years back with no post operative radiotherapy; however, she required hormonal supplementation therapy. She underwent an operation for a parotid tumour 7 years ago and received postoperative radiotherapy for the parotid tumour away from the site of the skull metastases. No local recurrence of the parotid tumour was noted. The initial diagnosis was that of a solitary intradiploic meningioma. Interesting clinico-radiological findings are presented.
How to cite this article:
Sousa J, Sharma R R, Pawar S J, Mahapatra A, Mishra G P. Solitary skull metastasis from mucoepidermoid mimicking a parotid tumour. Neurol India 2001;49:194 |
Skull metastases from the parotid tumours are rare entities. An interesting case of a mucoepidermoid parotid tumour metastasising to the skull is described in a patient who had, previously been operated for a pituitary adenoma about 20 years back, with no postoperative local radiotherapy.
A 55 year old female patient was admitted in the department of neurosurgery, Khoula Hospital in the year 1998 with the complaint of a painless slowly enlarging swelling on the right parietal region for 18 months. She was operated for a pituitary tumour 20 years back and was on hormonal therapy since then (prednisolone, thyroxin). She did not receive postoperative radiotherapy for the pituitary tumour. In 1992, she had been operated for a right parotid tumour (mucoepidermoid carcinoma) and received postoperative loco-regional radiotherapy for the tumour in the same year. On examination, there was a solitary right parietal swelling, 6.5x8 cms in size with a variegated consistency. It was irregular in shape, had a bosselated surface, was not infiltrating the scalp, and was non tender and non pulsatile. There were no scars or sinuses, but there were scanty hair in the region of the mass. The rest of the scalp was normal in appearance. The right parotid region showed evidence of a healthy scar and no palpable mass. She was neurologically well preserved, however the fundi showed evidence of optic atrophy, right more than the left, perhaps as a long standing effect of her operated pituitary tumour. Her vital parameters, biochemical
and hormonal status were within normal limits. The skull X-ray showed presence of a large bony defect in the right parietal region with trabecullar bony erosion resembling a 'soap bubble' appearance with thinning of the surrounding bony cortex and no periosteal reaction [Figure - 1]. Her computer tomography scan (CT scan) showed a right posterior parietal bony tumour with an intracranial extension and a minimal mass effect, but no shift of the midline structures was noted. The bone windows confirmed the extent of the bony destruction [Figure - 2]. A 'hot spot' could be demonstrated on the bone scan in the region of the right parietal mass. The mass was excised under general anaesthesia. At surgery, it was noted that this tumour was not adherent to the scalp and mainly arose fron the bone. A craniotomy bone flap was raised and total en-block resection of the tumour with the surrounding bone was carried out. The dura was found to be minimally adherent to the tumour, and could be well seperated. Postoperatively the patient had no neurological deficits and was discharged on the 5th day. The histo-pathological examination revealed a mucoepidermoid tumour with predominantly squamous component. She was referred to the oncologist, who did not consider further treatment, except a careful periodic follow up. She has remained asymptomatic for the last 10 months.
The salivary glands are comparatively simple structures, yet they are prone to large number of diseases which include infections (commonest), immunological diseases and a variety of neoplasms (rarest). The parotid tumours are currently estimated to comprise less than 3% of the total head and neck tumours excluding the skin cancers.[1],[2] The terminology used here is based on the nomenclature suggested by the World Health Organization.[3] Of the various tumours of the salivary glands 75-80% of the tumours are found in the parotid glands and of these 75-80% are benign pleomorphic adenomas. Benign adenolymphomas are the next common type of tumours, seen in 5-10% of cases.[4] These tumours are bilateral in 5% of the cases, may be multilple and occur in the older age group with a striking sex difference, as 85-90% of the cases are found in the male population.[4],[5] Mucoepidermoid tumours form 510% of all salivary gland tumours and nine tenths of them occur in the parotid gland.[4] Gray et al,[6] however, classified mucin containing salivary gland carcinomas as squamous cell carcinomas, if anaplasia was exhibited. Smith et al,[7] and Browand and Waldron[8] reported occasional cases of intraosseous growths within the mandible or the maxilla. Among the parotid tumours, mucoepidermoid carcinomas, adenoid cystic carcinomas and adenocarcinomas are commonly associated with distant metastases.[4] Common sites for the metastasis include lungs, liver, lymph node, bone and the spleen.[9] Metastasis to the skull bone is very rare. Exposure to radiation energy has been conclusively related to these tumours. Belsky et al[10] reported a 7 fold increase in these tumours in the survivors of the atomic explosion. A similar association has been reported in patients who had received radiation to the head and neck region.[11],[12],[13],[14]
The mucoepidermoid carcinoma is the most commonly radiation induced salivary tumour,[15] the latent period being 15-20 years. 75% of these tumours are in the parotid glands itself. Interestingly, our patient had no history of radiotherapy prior to the detection of the parotid tumour. Although, she was operated upon for a pituitary adenoma about 20 years back, she had not received post operative radiotherapy at that time. She had received post operative radiotherapy to the operated parotid region and had no local recurrence, but developed a late distant metastates to the cranium. To the best of our knowledge such a case has not been reported earlier. Goode et al[16] in their series reported that 16% of the
patients with mucoepidermoid carcinomas demonstrated regional lymph node metastases in 5.5%, lymph node and distant organ metastases in 8.5%, or only distant metastases in 1.7%. Aggressive loco-regional treatment to prevent distant failure has been advocated by many authors.[17],[18],[19] Distant metastases, however, are known to occur without local recurrence.[17],[20]
This patient, although having received radiotherapy for the operated parotid tumour, presented with a metastatic tumour with no evidence of a local recurrence. While no definite association with pituitary tumours has been reported earlier, it is possible that hormonal replacement therapy (steroids and thyroxin) in some way potentiated the growth of secondary tumour. The salivary gland tumours present a unique type of challenge to the surgeon and the pathologist alike; as their long natural history, wide spectrum of biological activity and their propensity for delayed recurrences/metastases contribute to their mystique.
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