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False localising signs of intracranial lesions are defined as signs not generally associated with disturbances of function at the site of the lesion.1,2 An intracranial tumour which has not metastasised may give rise to focal signs of disordered nervous function at a distance from itself in a number of ways. Even though these neurological signs are labelled as false localising signs, it is important to be aware that such signs are in no way “false”.3 Various cranial nerve palsies have been reported as false localising signs, with the sixth cranial nerve being the most common.1 According to Gassel, ninth to 12th cranial nerve palsies never provide false localisation.1 Since Dodge reported the first case of false localising sign involving the lower cranial nerve, only two cases have been reported in the literature.4 We report a third case of false localising sign involving the left ninth and 10th cranial nerves.
A 29 year old man presented to the medical department of our hospital with history of hoarseness of voice of 15 days duration, dysphagia of 1 week duration, and cough with expectoration and respiratory distress of 2 days duration together with history of fever. On examination, he was febrile, with a pulse of 100 bpm and blood pressure of 120/80 mm Hg. Respiratory examination revealed bilateral coarse crepitations. Neurological examination revealed absent gag reflex on the left side with deviation of the palate to the right side without any other neurological deficit. Indirect laryngoscopic examination revealed paralysis of left vocal cord.
Haematological examination revealed haemoglobin (Hb) 13.6%, a WBC count of 16 800/mm, and an erythrocyte sedimentation rate (ESR) of 120 mm/h. Chest x ray of the patient revealed bilateral pneumonitis. He was treated with antibiotics according to culture sensitivity. He progressively improved and was discharged. At discharge, he had persistent hoarseness of voice and vocal cord palsy on the left side. About 4 weeks later he presented with a history of bifrontal headache and was referred to our department. Neurological examination revealed bilateral papilledema and left palatal palsy with absent gag reflex. Other cranial nerves were normal. Motor and sensory system examination was normal. Occasional swaying to the left side on tandem walking suggested involvement of the cerebellar system. In view of these findings, a left posterior fossa mass lesion involving the lower cranial nerves such as a schwannoma was suspected. However, magnetic resonance imaging (MRI) of the brain revealed a large isointense homogenously enhancing mass lesion attached to the convexity dura (fig 1). It also revealed evidence of herniation of the cerebellar tonsils below the margin of the foramen of magnum and anterior displacement of the cerebellum causing stretching of the lower cranial nerves on the left side. The patient underwent midline suboccipital craniectomy and total excision of the lesion. The cerebellum was found compressed and deeply indented by the tumour. Postoperatively he improved neurologically. His gag reflex and palatal movements progressively improved and he was asymptomatic at 2 month follow up.
False localising signs are unexpected neurological deficits and reflect pathology distant from the expected anatomical locus. Prominent false localising signs are less common today, as diagnosis is usually made at an early stage.4 Cranial nerve involvement as a false localising sign is found in 12.5% of cerebral tumours.2 According to Gassel, false localising signs are more common in patients with signs of raised intracranial pressure. Due to the long intracranial course, sixth cranial nerve palsy is commonly associated with supratentorial mass lesions as a false localising sign.1 Most reports described single cranial nerve disturbance as a false localising sign. Rarely have multiple cranial nerve palsies been reported as false localising signs.4,5
Ehni proposed various mechanisms responsible for false localising signs. These include: (i) general compression of a nerve having a long course; (ii) meningitis; (iii) oedema and gliosis; (iv) metastatic deposits; (v) infarctions at a distance from the primary lesion due to occlusion of a vessel by a neoplasm or by cerebral herniation through a dural aperture; (vi) gross brain displacement involving the brainstem and causing traction of cranial nerves and kinking of cranial nerves over vessels; and (vii) brain stem shifting to the opposite side causing tentorial notching, pressure at the rim of the foramen magnum, pressure at points of emergence of cranial nerves, and involvement of the corticospinal tract.6 Gassel pointed out that false localising signs are commonly associated with intracranial meningiomas as they are discrete tumours that tend to compress and displace the brain rather than infiltrate cerebral tissues.1 He also commented upon the rigidity of the bony skull and its dural compartments, as well as the outcome of pressure within the skull causing movement of parts of the brain towards the tentorial opening and foramen magnum resulting in herniation pressure on various blood vessels.1 O’Connell suggested that displacement of the brainstem by the tumour results in slackening of the horizontally directed nerves such the seventh to 11th cranial nerves and stretching of the anteriorly directed nerves such as the fifth and sixth around the lateral margin of the dural foramen.7 Matsuura and Kondo proposed that displacement rather than rotation of the brainstem, causing compression and/or angulation of the affected nerve rather than stretching or traction, is the most significant factor for inducing contralateral trigeminal neuralgia and hemifacial spasm.5 However, according to Haddad and Taha, rotation of the brainstem shifts the basilar artery or loop of its branches close to the trigeminal nerve at its root entry zone and causes trigeminal neuralgia.8
Most cranial nerve dysfunctions presenting as false localising signs appear as hypoactive dysfunctions.1,6 Rarely has hyperactive dysfunction syndrome involving the cranial nerve, such as trigeminal neuralgia or hemifacial spasm, been reported in the literature.5,8 False localising sign involving lower cranial nerves is extremely rare with just two cases reported in the literature.4 Maurice-Williams proposed two mechanisms causing lower cranial nerve palsy: firstly, cerebellar hemisphere impacting the foramen magnum, causing reaction and oedema and thereby compression of the lower cranial nerve and secondly, displacement of the cerebellum to the contralateral side, forcing the brainstem to the ipsilateral side and thus exerting traction on the contralateral lower cranial nerve.4 The case reported here involved a large cerebellar convexity meningioma causing cerebellar herniation downwards into the foramen magnum and anteriorly into the lateral cerebello-medullary cistern which resulted in stretching of the lower cranial nerves. The cranial nerve function improved following excision of the tumour. Awareness of the possibility of false localising signs and the conditions in which they are most likely to occur is very important as they may be indicative of serious life threatening pathology within the neural pathway.3
Competing interests: none declared