FAVOURABLE TUMOURS OF THEPOSTERIOR CRANIAL FOSSA

LESLIE OLIVFR, M.B., F.R.C.S., F.A.C.S.Neurosurgeont, Charing Cross Hospital, West London Hospital, Royal Northern Hospital, West End Hospital for

Neurology and Neurosurgery, London

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FIG. i.-Enlargement of the lateral and third ventricles produced by atumour in the posterior fossa.

If the diagnosis of a benign intracranial tumouris made soon enough, a favourable outcome cannowadays be expected after operation. Therefore,when a patient is shown to have an intracranialtumour, its pathological nature must be provenbeyond doubt. Benign tumours may occur any-where insidc the skull, but in this article discussionis limited to those of the posterior fossa.One or more of the following effects may be

brought about by expanding lesions of the posteriorfossa. The flow of cerebrospinal fluid through theaqueduct and fourth ventricle may be obstructedand the resulting hydrocephalus is revealed byfrontal headache, vomiting and papilloedema(Fig. i). Suboccipital headache occurs in somecases in association with descent of a ccrebellarpressure cone through the foramen magnum. Alesion expanding from a lateral position towardsthe midline may cause lateral nystagmus, which isslower and of greater amplitude when the eyes

look towards the side of the lesion. Hypotonia,incoordination, intention tremor, dysdiadocho-kinesia and past-pointing may be demonstratedin the arm on the side of the tumour and theoutstretched arm may deviate spontaneously out-wards and downwards. Sometimes there ishypotonia and incoordination of the homolateralleg and veering or falling towards the side of thelesion. A tumour expanding in the midlinebehind the brain-stem tends to cause ataxia andhypotonia of the lower limbs.

Pressure may occur on pyramidal fibres oneither or both sides. Contralateral pyramidal signsare produced by direct pressure of the tumour onthe pons, whereas homolateral pyramidal signs areproduced by the cerebral peduncle of the oppositeside being forced against the free edge of- thetentorium cerebelli and consequent pressure onpyramidal fibres which cross below in the medullaoblongata to the side of the lesion. Extrinsic

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August I960 OLIVER: Favourable Tumours of the Posterior Cranial Fossa 499

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FIG. 2.-Ventriculography with air (negative contrast)and Myodil (positive contrast). The air is in theanterior horns of the lateral ventricles and anteriorend of the third ventricle showing advanced hydro-cephalus. On the right there is some Myodil inthe occipital horn. The rest outlines the posteriorend of the distended third ventricle, the aqueductdisplaced to the left with its upper part distended andits lower part compressed, and the fourth ventriclewhich is deformed and displaced to the left. Theseeffects were produced by an acoustic tumour on theright.

tumours are likely to compress the cranial nervesof the posterior fossa early in their evolution,whereas intrinsic tumours tend to compress themlate, or not at all. For reasons as yet unexplained,cranial nerve palsies occasionally occur on the sideopposite to the tumour. Severe compression ofthe medulla oblongata may occur from an ex-panding lesion arising anywhere in the posteriorfossa, and may give rise to vertigo, dysarthria,dysphagia, repeated vomiting, bradycardia, slowingof respiration and eventually Cheyne-Stokesrespiration.

Unilateral or bilateral external rectus paralysisoccurs with some tumours in the posterior fossadue to stretching of the abducens nerves. This isbrought about by descent of the brain-stem pro-duced by increasing pressure in the ventriclesabove the tentorium.

Bilateral inferior temporal scotomas or bi-temporal lower quadrantic field defects (never acomplete bitemporal hemianopia) may result from

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Fic. 3.-A lateral view taken in the same case as Fig. 2.Air shows distension of the lateral ventricles, andMyodil shows sharp forward angulation of theaqueduct which is also distended above and con-stricted below.'

pressure on the optic chiasm by the anterior .endof the distended third ventricle.

Slowly expanding intrinsic cerebellar tumours(e.g. astrocytomas and haemangioblastomas) quiteoften cause little or no cerebellar disturbance andgive no evidence of involvement of cranial nervesor the brain-stem, but present with manifestationsof raised intracranial pressure alone. Such tumoursare easily mistaken for ' silent ' tumours arising inother parts of the cranium (e.g. prefrontal andpretemporal regions). Furthermore, frontal andeven parietal lesions occasionally produce mildcontralateral ' cerebellar' signs. Rapidly expand-ing lesions, such as cystic tumours and cerebellarhaemorrhage, cause acute medullary compressionand acute hydrocephalus.

InvestigationsVentriculography usually reveals dilatation of

the lateral ventricles and third ventricle. Dis-placement, deformity and dilatation of the aque-duct and fourth ventricle may also be demon-strated. Tumours in the posterior fossa some-times cause upward displacement of the thirdventricle, or upward curving of the posterior hornof the lateral ventricle on the side of a laterallyplaced tumour. Marked indentation of theoccipital horn occurs with dumb-bell meningiomasarising from the tentorium and growing supra-and infra-tentorially. Positive contrast ventri-culography with Myodil (i to 2 ml.) injectedthrough the anterior horn of one of the lateral

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500 POSTGRADUATE MEDICAL JOURNAL August I960

ventricles gives more reliable information regardingthe aqueduct and fourth ventricle than air ventri-culography (Figs. 2 and 3). However strong theclinical evidence of a posterior fossa tumour maybe, ventriculography should always be doneexcept, perhaps, when there is indisputable evi-dence of an acoustic tumour, which often pro-duces a characteristic syndrome. Vertebral angio-graphy is more difficult and more dangerous thancarotid angiography. Therefore it is not em-ployed if the necessary information can beobtained otherwise. Aneurysms, vascular mal-formations and vascular tumours are outlined inangiograms.

Types of Benign TumoursAstrocytomnas are the commonest intrinsic cere-

bellar tumours. The maximum incidence is duringthe first two decades. In the cerebellum most astro-cytomas are cystic and benign (Grade I). Fre-quently there is a large cyst with a small muraltumour. The cystic fluid is yellow and contains alarge amount of protein. Removal of the muralnodule is usually all that is required.

Haemangioblastomas (Syn. Angioreticulomas).These tumours occur most often in the cerebellum;they are rare elsewhere in the nervous system.They are more often cystic than solid. The cyststend to be large and contain mural tumours likethose in cystic astrocytomas of the cerebellum.Unlike the latter tumours however, haemangio-blastomas are found most often in adults, and theyshow themselves earlier in women than in men.Thus in women the maximum incidence occursbetween twenty and forty years, whereas in menit is between forty and sixty years. Sometimesthese tumours are familial; they then tend to bemultiple. Therefore vertebral angiography shouldbe done for suspected haemangioblastomas whenthere is a family history of these tumours,otherwise multiple tumours may be overlooked atoperation. The association with haemangio-blastomas elsewhere and cysts in the liver, pancreasor kidney, is known as Lindau's syndrome.Angioma of the retina (von Hippel's disease) maybe one of the lesions forming part of Lindau'ssyndrome.

Acoustic Nerve Tumours (Syn. Acoustic Neurino-mas, Schwannomas, Perineural Fibroblastomas orNeurilemmomas). These tumours are thought toarise from the endoneurium of the acoustic nervewithin the internal auditory meatus. They growin the subdural space, and as they expand comeinto relationship with the trigeminal nerve, cere-bellum, pons, and eventually also with the ninth,tenth, eleventh and twelfth cranial nerves (Fig. 4).They are usually solid tumours but are commonlysurrounded by a cyst formed by the arach-

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FIG. 4.-A right-sided (readers' left) acoustic tumour.There is a severe degree of indentation of the ponsand medulla oblongata.

noid. Bilateral acoustic tumours are sometimesfound in the ' central' type of von Reckling-hausen's neurofibromatosis. Acoustic tumours arecomposed of interlacing bundles of spindle cellscontaining elongated nuclei. The cells tend to bearranged in rows (' palisading') and some formwhorls around blood vessels. Reticulum fibrilsare conspicuous between cells. Nerve fibres arerarely seen.These tumours affect both sexes equally, and

symptoms begin in middle age and have usuallybeen present for two to three years before theneurosurgeon is consulted. The first symptom isgradually progressive deafness in one ear, fre-quently accompanied by tinnitus and dizziness(severe vertigo is rare). Involvement of the vesti-bular division of the eighth cranial nerve isdemonstrated by the caloric test.

Paraesthesia in the distribution of the fifthcranial nerve is common, but trigeminal pain israre. Absence of the corneal reflex may be the onlysign of involvement of this nerve. Strangelyenough, there is little or no evidence of com-pression of the facial nerve. There may be achingpain in the occipital muscles and tenderness behindthe homolateral mastoid process. Later there arecerebellar signs. In some cases, compression ofthe brain-stem produces pyramidal signs on either

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August I960 OLIVER: Favourable Tumours of the Posterior Cranial Fossa 50I

or both sides. Later there are signs of increasedintracranial pressure (headache, vomiting andpapilloedema, abducens nerve paralysis). Ex-tension of the tumour to the tenth and eleventhcranial nerves causes unilateral palatal, pharyngealand laryngeal paralysis and also partial paralysisof the sternomastoid and trapezius muscles.

Radiography often shows enlargement of theinternal auditory meatus or sometimes consider-able erosion of the petrous bone. When thesyndrome is atypical, positive contrast ventri-culography (Myodil I to 2 ml.) is carried out toshow the aqueduct and fourth ventricle.Removal of acoustic tumours is carried out

through a unilateral approach with the patient inthe sitting position. Operation still has a con-siderable mortality (up to 25 per cent.) becausethese tumours are usually referred to the neuro-surgeon when there is marked indentation of thebrain-stem and advanced hydrocephalus. De-compression alone is valueless, for acoustic tumoursare firmly attached to the petrous bone and there-fore the pressure on the brain-stem is not relieved.The facial nerve is not seen during operation, andfacial palsy usually results. It is treated by facial-hypoglossal or facial-accessory anastomosis.

Meningiomas in the posterior fossa may beattached to any part of the dura mater, but usually

arise somewhere along the transverse or sigmoidsinuses. Sometimes they grow in the cerebello-pontine angle and mimic acoustic tumour s.Dumb-bell meningiomas of the tentorium are rar etumours which grow upward to indent theparieto-occipital lobe and downward into theposterior fossa. In the removal of meningiomas ofthe posterior fossa, the transverse sinus on oneside may be divided or excised when necessary, asthere is usually an anastomotic channel betweenthe two transverse sinuses. The presence of thisconnection may, however, be verified preopera-tively by venography (the superior longitudinalsinus is injected through a burr-hole with 20 ml.Of 42.5 per cent. diodone solution) and serialX-rays are taken.

Epidernioid Tumours (Syn. Cholesteatomas,Pearly Tumours of Cruveilhier). These are con-genital tumours arising from the meninges andconsisting of a capsule of epidermal tissue en-closing a mass of epithelial debris and cholesteitolcrystals. They are not to be confused with theinflammatory type of ' cholesteatoma' caused bychronic infection of the middle ear and mastoid.The whole of the contents of the ' cyst' and asmuch of the capsule as possible must be removed,for if some cholesterol remains it causes an asepticmeningitis which can be fatal.

NEWCASTLE SY1MPOSIUM(Postgraduate Medical Journal, April 1960)

Price 6s. 6d. post freeTHE THROMBOGENIC HYPOTHESIS AND SOME RECENT TRENDS AND DEVELOP-

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CURRENT RESEARCH IN MULTIPLE OLD AGESCLEROSIS Martin Roth, M.D., F.R.C.P., and D. W. K.E. J. Field, M.D., M.S., Ph.D., and Henry Kay, M.A., B.M., D.P.M.

Miller, M.D., F.R.C.P. STUDIES OF LUNG FUNCTION INTHE SURGICAL TREATMENT OF PARKIN- CHILDRENSON'S DISEASE L. B. Strang, M.B., M.R.C.P., and S. D. M.John Hankinson, M.B.(Lond.), F.R.C.S. Court, M.D., F.R.C.P., D.C.H.

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