Preventing damage to miniature-loudspeaker by means of dynamic detection of excessive diaphragm displacement.

The rapid development of consumer electronics and the extensive use of mobile devices require the ample use of miniature-loudspeakers for audio applications. The demand for better sound pushes manufacturers to design digital signal processing (DSP) chips (smart amplifiers), which in turn could cause unpleasant sound due to distortion and parameter nonlinearity or transducer damage caused by large diaphragm excursion or voice-coil (VC) burn. This article presents a methodology for nonlinear parameter estimation using an inverse method and displacement limiter for large VC displacement-dependent transducer damage prevention. A set of transduction equations is employed to inversely determine parameters using a polynomial expression. The appropriate selection of an objective function incorporating the unknown vector of nonlinear parameters leads to the adjoint problem that requires a gradient solution. A numerical solver is provided to obtain the VC displacement, current, and derivatives using a robust hybrid spline differential method. The dynamic limiter is proposed to control the peak values of the VC velocity so as to limit an excessive displacement which prevents impulsive damage to the receiver and further application of the DSP board. Numerical and experimental results indicate that the proposed method has high efficiency and can be widely used in transducer applications.

Preparation and thermal studies on tetranitrodibenzo tetraazapentalene (TACOT): a thermally stable high explosive.

Thermally stable high explosive, tetranitro-2,3,5,6-dibenzo-1,3a,4,6a-tetraazapentalene (TACOT) was synthesized and characterized during this work. Thermo analytical techniques (TG and DSC) were applied to study the thermal decomposition behaviour of TACOT in comparison with benchmark thermally stable high explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). Kinetic parameters such as reaction order, activation energy and pre-exponential factors were computed from the thermal data. The activation energy for TACOT (292 kJ/mol) was found 1.5 times to that of TATB (200 kJ/mol), which can account for its higher thermal stability and can be attributed to pentalene moiety in the former.

Synthesis, characterization and thermolysis studies on triazole and tetrazole based high nitrogen content high energy materials.

This paper reports the synthesis, characterisation and thermolysis studies of hydrazinium azotetrazolate (HAZ) and 1,1'-dinitro-3,3'-azo-1,2,4-triazole (N-DNAT). TGA and DSC results suggested that HAZ decomposes in the range of 150-180 degrees C and N-DNAT in the range of 160-170 degrees C, respectively. The pattern of decomposition of HAZ dihydrate and N-DNAT has been predicted with the help of pyrolysis GC/MS technique and a probable decomposition mechanism has been proposed. The theoretically predicted performance data suggests the potential nature of HAZ and N-DNAT for their use in propellant/explosive as well as in gas generator formulations.

Choroid plexus papilloma of the posterior third ventricle during infancy & childhood: report of two cases with management morbidities.

We report two cases of posterior third ventricular choroid plexus papilloma, one in an 8-month-old infant and another in a two-year-old child. These cases presented with features of obstructive hydrocephalus. Both these patients underwent a ventriculo-peritoneal (VP) shunt surgery prior to the tumor excision. Following the VP shunt surgery both patients developed ascitis requiring exteriorization of the abdominal end of the shunt. There was a clear proof of CSF overproduction: 1400-1500 ml/day in the eight-month-old infant and 900-1200 ml/day in the two-year-old child. In the former it was transient and could be treated with revision of the VP shunt whereas in the second case a ventriculo-arterial shunt had to be done. In the second case a staged reduction cranioplasty was also performed for an enormously enlarged head (head circumference--74 cm). Interesting clinical and radiological findings and useful management strategies are described.

Sudden bilateral foot drop: an unusual presentation of lumbar disc prolapse.

Bilateral acute foot drop is reported in a 30-year-old healthy male. He presented with a 7-day history of sudden severe backache, radiating to both the lower limbs and 1-day history of sudden bilateral ankle weakness that progressed to bilateral foot drop within 6 hours. He also developed retention of urine. Investigations revealed a large central disc prolapse at L3-4 with significant canal stenosis at that level. Following surgery the patient had progressive improvement.

Long term outcome in patients with severe head injury and bilateral fixed dilated pupils.

Patients with severe head injury with bilateral dilated unreactive pupils are considered to have a grave prognosis. Hence proper planning and aggressive management becomes mandatory for achieving good results. We present the outcome of consecutive 166 patients with severe head injury, admitted between January 1996 and December 2000 and analysed retrospectively. All the patients had an initial GCS of 8 or less and post resuscitation bilateral dilated unreactive pupils. Our aim was to analyze the long term outcome in these patients and identify the other significant prognostic factors. Of the 166 patients, 42 (25.30%) had a functional outcome (good recovery in 10.24%, moderate disability in 15.06%), and 124 (74.69%) had a poor outcome (death in 58.43% and severe disability in 16.26% of cases). There were 45 patients with polytrauma and 24 of these patients (53.33%) succumbed to the injuries. Obliteration of the basal cisterns and contusion were the common CT scan findings. Factors adversely affecting the survival included age of the patient, polytrauma with shock, initial GCS of 3 or 4, and compression of the basal cisterns on the initial CT scans. At follow up, most of the patients with a functional outcome showed a significant improvement in their motor function but continued to have neuro-behavioral and cognitive deficits.

Vagal schwannoma of the cerebello-medullary cistern presenting with hoarseness and intractable tinnitus: a rare case of intra-operative bradycardia and cardiac asystole.

Schwannomas arising from the lower cranial nerves (IX-XI) are rare, constituting only 3% of all intracranial schwannomas unassociated with neurofibromatosis. A great majority of these tumours present as jugular foramen lesions and less commonly they occur along the extracranial course of these nerves. An intracisternal location is extremely rare. We report a case of vagal schwannoma purely in the cerebello-medullary cistern causing distortion of the medulla oblongata. Total microsurgical excision of this tumor, arising from one of the rootlets of the vagus nerve, was achieved with preservation of the 9th, 10th and 11th cranial nerves.The intraoperative course was complicated by two episodes of complete cardiac asystole, each lasting for 4(s), and six episodes of severe bradycardia. The patient was relieved of his intractable tinnitus but continued to have a hoarse voice due to an ipsilateral partial vocal cord palsy.

Fatal rhino-orbito-cerebral mucormycosis in an apparently normal host: case report and literature review.

Fungal infections of the central nervous system (CNS) are fortunately rare but remain challenging problems occurring mostly in immunocompromised individuals, with protean manifestations, unpredictable course and unfavorable outcome in many cases despite aggressive neurosurgical intervention and recent antifungal drugs. Rhino-orbito-cerebral mucormycosis is a potentially lethal opportunistic fungal infection with rapid progression and high mortality. Its pathogenic nature becomes evident when the patient's general resistance is compromised. We present a case of an invasive rhino-orbito-cerebral mucormycosis in an apparently normal adult who initially developed mild paranasal sinusitis and later developed status epilepticus and despite an aggressive management died. Interesting clinical, neuroimaging and histological findings are described, and the possibility of fatal mucormycosis in an apparently normal host is highlighted.

Pharyngeal perforation and spontaneous extrusion of the cervical graft with its fixation device: a late complication of C2-C3 fusion via anterior approach.

Stabilisation of the fracture-dislocation of the cervical spine is achieved effectively by anterior or posterior or combined methods with attendant short and long term benefits, risks and complications associated with each procedure. Recently anterior methods have gained wider acceptance. A variety of preoperative and postoperative complications associated with anterior cervical fusion are well recognised. However, the delayed pharyngeal or oesophageal perforation is a rare, serious and life threatening complication of an anterior cervical internal fusion.The authors report a case of delayed pharyngeal perforation and spontaneous extrusion of the C2-C3 graft with its fixation device. After coughing out the entire gamet of the graft with the fixation pin, the patient was relieved of excruciating pain and dysphagia and had no significant morbidity thereafter over a 12-year follow up period. Relevant aspects are discussed with a review of the pertinent literature.

CT stereotaxy guided lateral trans-cerebellar programmable fourth ventriculo-peritoneal shunting for symptomatic trapped fourth ventricle.

A trapped fourth ventricle is a rare clinico-radiological entity producing symptoms suggestive of a progressive posterior fossa mass lesion. It is mainly reported in children as a late complication of lateral ventricular shunting to relieve infantile post-meningitic or post-hemorrhagic hydrocephalus. Optional treatment of the trapped fourth ventricle remains controversial. Placement of fourth ventricular shunting via a conventional midline approach can be fraught with complications in about 40% of the patients. Authors report a successful CT Stereotaxy guided high pressure (80 mm H(2)O) programmable fourth ventriculo-peritoneal shunting via a lateral trans-cerebellar approach in a 14-year-old girl with a trapped fourth ventricle, which occurred as a late complication of ventriculo-peritoneal shunting in her infancy. Her preoperative symptoms of raised intracranial pressure, bobble-head doll syndrome and bilateral abducens palsies completely improved following the surgery. Lateral trans-cerebellar stereotactic placement of the fourth ventricular catheter and the use of high-pressure (low flow) programmable shunt (to avoid complications associated with over drainage) are beneficial in some patients with trapped fourth ventricle.

Cranio-spinal enterogenous cysts: clinico-radiological analysis in a series of ten cases.

Enterogenous cysts are rare congenital lesions resulting from dysgenesis during the third embryonic week at the time of notochord development and the transitory existence of the neurenteric canal. Enterogenous cysts are usually lined by mucus secreting epithelium resembling that of the gastrointestinal tract. The inclusion of the endodermal elements in the spinal canal may produce extradural, intradural extramedullary or intradural intramedullary cystic lesions. The endodermal inclusions producing cysts in the intracranial compartment are extremely rare, especially in the supratentorial region. Plain X-rays may show concomitant cranio-spinal anomalies. However, CT and MRI scans show better definition and characterisation. Total excision is the procedure of choice in these benign cysts with favourable long term prognosis. Approximately 100 histologically proven cases have been described, with a few exceptions, as isolated case reports the authors report a detailed analysis of the clinico-radiological aspects of a series of ten patients with cranio-spinal enterogenous cysts with a review of the literature.

Spinal cord and cauda equina compression in 'DISH'.

Diffuse idiopathic skeletal hyperostosis (DISH) has long been regarded as a benign asymptomatic clinical entity with an innocuous clinical course. Precise information is lacking in the world literature. Authors report the results of a retrospective analysis of 74 cases of DISH. Eleven patients presented with progressive spinal cord or cauda equina compression. In nine cases ossified posterior longitudinal ligament (OPLL) and in two cases ossified ligamentum flavum (OLF) were primarily responsible. Surgically treated patients (eight) had far better outcome as compared to the patients managed conservatively, as they had refused surgery. 'DISH' is neither a benign condition, nor it always runs a innocuous clinical course. In fact, in about 15% of the cases, serious neurological manifestations occur, which may require a major neurosurgical intervention.

Sciatica due to malignant nerve sheath tumour of sciatic nerve in the thigh.

Malignant peripheral nerve sheath tumour (MPNST) is a rare malignant neoplasm arising from the supportive non-neural component of the peripheral nerves. An unusual case of pain and weakness of the foot and calf muscles due to a giant MPNST of the sciatic nerve in the posterior compartment of the thigh is presented. The patient was already investigated as a case of sciatica due to a lumbar disc disease with a negative magnetic resonance imaging and then unsuccessfully operated elsewhere twice, with a misdiagnosis of tarsal tunnel syndrome. Neurosurgical referral prompted a diagnostic magnetic resonance study of the thigh, revealing the lesion, which was completely excised microsurgically with total relief in the pain and partial improvement in the weakness and sensations in the sole of the foot.

Solitary skull metastasis from mucoepidermoid mimicking a parotid tumour.

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.

Giant ependymal cyst of the temporal horn -- an unusual presentation. Case report with review of the literature.

Primary benign cystic lesions in the brain are uncommon. However, extracerebral cysts like arachnoid cyst, epidermoid cyst and craniopharyngiomas are fairly common lesions. Also, colloid cyst in the third ventricle, dermoid cyst and endodermal cyst in the extracerebral location are not uncommon. On the contrary, intraventricular ependymal and choroidal cysts in the intraventricular location are infrequent. Surgical intervention is warranted in cysts, which produce a mass effect and raised intracranial pressure. We present an interesting case of a giant intraventricular ependymal cyst in the temporal horn in a 14-year-old boy, who presented with recent onset of headaches and epilepsy. He also had long-standing progressive proptosis of the left eye and left temporal bossing. Excision of this cystic lesion was curative. Interesting clinical and neuroimaging features are presented.

Primary orbito-cranial adenoid cystic carcinoma with torcular metastasis: a case report and review of the literature.

Adenoid cystic carcinoma is a rare neoplasm arising from the exocrine glands such as salivary glands, lachrymal glands, upper respiratory tract, breast or uterine cervix. Intracranial involvement is commonly from direct skull base involvement, although metastasis may rarely be seen. The predisposition of the adenoid cystic carcinoma for perineural and perivascular invasion is the prime reason for the locally invasive character of the tumour, often extending into the cranium via foramina at the skull base. The authors report a case of primary orbito-cranial extradural adenoid cystic carcinoma and cranial metastasis away from the primary site. This patient initially had a local excision, and later an exenteration of the right eye followed by with radiotherapy. Within months she presented with an extradural cranial recurrence, distant torcular metastasis without any neurological deficit. Craniotomy and radical excision was undertaken as these tumours have slow growth rates, and long term survival of the se patients even in the presence of local recurrence and metastasis has been well documented.

Congenital and late-onset primary haemangiomas of the temporalis muscle: case report.

We report on two patients with haemangiomas of the temporalis muscle, one congenital and one of late onset, which were diagnosed on computed tomography. Both were resected successfully and both patients are well with no signs of recurrence 3(1/2) years and 18 months later, respectively.

Schwannoma of the suprascapular nerve presenting with atypical neuralgia: case report and review of the literature.

Compressive lesions of the suprascapular nerve produce weakness and atrophy of the supra- and infraspinatus muscles and a poorly defined aching pain along the posterior aspect of the shoulder joint and the adjacent scapula. Entrapment neuropathy of the suprascapular nerve is fairly common whereas tumorous lesions are rare; among the latter ganglion cysts are frequently seen. An isolated solitary schwannoma of the suprascapular nerve presenting with atypical neuralgic pain is exceptional. The location of a schwannoma under the firm deep cervical fascia in the posterior triangle of the neck is implicated in the genesis of neuralgic pains mimicking the suprascapular entrapment syndrome. One such case is reported with discussion of the relevant clinical features.

An unusual presentation of an intra-parenchymatous frontal yolk sac tumour : case report.

Yolk sac tumours are rare conditions among the germ cell tumours. Intracerebral germ cell tumours are exceedingly rare. A 15 year old girl presenting with a one week history of raised intracranial pressure is described. She had bilateral papilloedema and a right 6th nerve palsy. CT scan showed an intra-parenchymatous right frontal ring enhancing lesion of 2 cms diameter. The patient underwent microsurgical total excision of the tumour, followed by chemotherapy. She was asymptomatic at three years following surgery.