Postgraduate Medical Journal (1988) 64, 626-630

Trichinosis diagnosed by computed tomography

Louis Kreel,1 Wai S. Poon2 and J.C. Nainby-Luxmoore3

'Departments of Diagnostic Radiology & Organ Imaging and Surgery, Prince of Wales Hospital, 2TheChinese University of Hong Kong, Shatin, NT, Hong Kong and the 3Department of Paediatrics, BritishMilitary Hospital, Hong Kong.

Summary: Trichinosis is a worldwide disease contained by good husbandry and culinary practice,presenting unexpectedly in individual cases or mini-epidemics. The disease varies greatly in itsmanifestation and severity although when marked can be recognized by fever with myositis andperiorbital oedema. Antibody tests are specific but the appearances on computed tomography ofthe brain are sufficiently characteristic to allow a confident diagnosis. Two cases where suchappearances led to the diagnosis are reported.

Introduction

A mini-epidemic of trichinosis has lately been des-cribed but the radiological manifestations were notconsidered.1 In Chinese cuisine pork is thinly slicedbut the recent popularity of barbecuing has intro-duced the risk of infestation by trichinosis in HongKong. Furthermore the presence of non-Chineseincreases the possibility of encountering this diseasein Hong Kong. Two cases of trichinosis arereported, one in a Nepalese child and the other inan indigenous Hong Kong resident, where thecomputed tomographic (CT) appearances led to thediagnosis being made.

Case reports

Case 1

A girl of 8 years of age from Nepal was referredfor a CT examination following a left sided focal fitfollowed by an upgoing left plantar reflex. As aneonate she had had meningitis, probably haemo-philus, when a left sided focal fit had also occurred,but since the original illness she had been well withno sequelae. However, a skull radiograph showedenlargement of the right middle fossa with elevationof the lesser wing of the sphenoid and slight

enlargement of the superior orbital fissure (Figure 1).On physical examination there was no abnor-

mality. Full blood count and ESR were normalapart from 18% eosinophilia (white cell count9.3 x 109/1). An arachnoid cyst, possible temporalhorn hydrocephalus, or slow growing glioma wereconsidered as possibilities in view of the skullradiograph.The CT examination revealed two areas of low

attenuation in the white matter, one in the rightpostero-superior aspect of parietal lobe and theother adjacent to the falx in the right frontal lobe(Figure 2). Following intravenous contrast enhance-ment with 40 ml of conray '280' a small enhancedring lesion of 8mm was found adjacent to each ofthe low density oedematous areas as well as asimilar lesion in the left posterior parietal regionadjacent to the falx (Figure 3).

Trichinosis was diagnosed and subsequently theantibody test was found to be positive while sero-logy for cysticercosis and angiostrongylus werenegative.

Case 2

A man aged 43 presented with headache for 3 yearsbut worse in the last few months, maximal over theright parietal region. He gave a history of repeatedminor head trauma and in addition a previous CTbrain scan was said to have shown a 'rice-sized'tumour in the region of the painful area.

© The Fellowship of Postgraduate Medicine, 1988

Correspondence: Professor L. Kreel M.D., F.R.C.P.,F.R.C.R.Accepted: 7 March 1988

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Figure 1 Case 1. (a) Lateral view of the skull showingthe forward displacement of the middle cranial fossa(arrows). (b) In the frontal view elevation of the lesserwing of the sphenoid on the right is shown (arrow)and slight widening of the superior orbital fissure. (c)The basal section of the CT examination confirms theenlargement of the right middle fossa (arrow).

Figure 2 Case 1. Two areas of oedema of whitematter are present, (a) in the right frontal region(arrow) and (b) in postero-superior aspect of theparietal lobe.

Apart from occasional visits to Canton thepatient had not been abroad. He could not recallany episode of gastrointestinal upset, severe systemicillness or muscle aches and pains.

General and neurological examination wasnormal apart from 2 small nodules in the scalp onthe right side shown to be lipomata followingexcision. The peripheral white cell count was8.1 x 109/1 with 1% eosinophils.CT brain scan showed 3 small calcified rings of

3-8 mm, one lying adjacent to the anterior aspect of

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Figure 3 Case 1. (a) and (b) Following contrastenhancement small ring lesions typical of trichinosishave been demonstrated (arrows).

the right frontal horn and the other two close tothe left posterior horn of the lateral ventricles(Figure 4). There was slight contrast enhancement ofthe anterior lesion (Figure 5) but no surround-ing oedema.

Trichinosis was diagnosed and the subsequentserology was shown to be strongly positive forTrichinella spiralis larval antibodies (enzyme-linkedimmunoabsorbent assay). Following a 6 day courseof oral mebendazole 100mg twice daily his head-aches rapidly subsided.

Discussion

Recent editions of major radiological textbooks2-5do not include trichinosis let alone cerebral trichi-nosis in their indices and even in textbooks relatedspecifically to imaging of the brain6'7 there is nomention of trichinosis. Nor is there a differentialdiagnosis of multiple cerebral lesions 3-8mm in

Figure 4 Case 2. (a) and (b) Three small calcified ringdensities can be seen, varying in size from 3-8 mm,typical of trichinosis (arrows).

diameter, all the same size, nodular or ring-likewith a surrounding halo of low attenuation.

Similar lesions are illustrated but none show allthe above features particularly all being less than8mm, some having ring calcifications and enhanc-ing after intravenous contrast medium. The lesionsshown include cerebral tuberculosis, sarcoidosis,cysticercosis and various fungal infections such asnocardia, histoplasmosis, and cladosporium.6Furthermore, a computer search and the medicalindex failed to reveal articles other than thosequoted8'9 where the CT lesions are illustrated.However in those shown the features were aspreviously described. Yet trichinosis and particu-larly cerebral disease is an ever present hazard dueto the ubiquitous occurrence of the parasite.10 Inthe personal experience of the senior author inIndia, trichinosis can be confidently diagnosed withthe characteristic CT appearances as shown by thetwo cases described in this communication.

Multiple sclerosis and small cerebral infarcts

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Figure 5 Case 2. Following contrast enhancementthere is slight uniform staining of the surroundingtissue (arrow).

also produce scattered 8 mm lesions on contrastenhancement but do not show a ring pattern orsurrounding oedema and the clinical presentationwith epilepsy is unusual. Furthermore, multiplesclerosis is rare in the indigenous population of HongKong.The CT features of trichinosis on brain scans

appear to be sufficiently specific for a confidentdiagnosis when either small calcified or contrastenhanced rings are demonstrated, a sign particu-larly helpful in cases presenting with epilepsy.When only low attenuation areas either in thecorona radiata or when larger areas of low attenua-tion indicating vasogenic oedema in the deep whitematter are demonstrated, contrast enhancementbecomes necessary for. a specific diagnosis.

Until recently trichinosis had not been reportedfrom Hong Kong but the changing life style,recourse to fast foods and eating barbecued meat islikely to lead to many more cases being diagnosedin this area.1The ingested viable cysts produce tapeworms that

subsequently inhabit the duodenum giving rise tolarvae localizing predominantly in striated musclebut are also found in lung, myocardium and

brain.10 The florid illness is one of fever, muscularaches and pains, myocarditis, respiratory andcentral nervous system symptoms as well as diarr-hoea and periorbital oedema. The initial disease canbe so severe as to be fatal or at the other extreme,the initial infestation can be so mild as to gounrecognized. The severity appears to depend onthe number of viable cysts ingested.","2The vast majority of trichinous infections in man

are subclinical'3 while in the latest mini outbreaksin France8 patients were severely ill from eatingunderdone or raw horsemeat (steak tartare). Larvalcounts of more than 1000/g of muscle tend to befatal'3 unless treated early with steroids and anti-helminthics in adequate dosage. Pickled pig's feetand bear meat are especially hazardous, the latterbecause the variety of Trichinella in polar bearmeat is particularly resistant to cold, remaininginfective for up to 24 months after being stored at- 18'C.14 However, adequate cooking at 80'Cremains the best safeguard against trichinosis.'5

In more severe cases there may be symptoms andsigns of meningitis, encephalitis, paresis, aphasia,hemianopia, sphincter disturbances, cranial nervedeficits and spinal cord lesions.""I2The severity of central nervous system infestation

depends not only on the presence of the larvae butalso on the eosinophilic reaction. A neurotoxin hasbeen isolated from eosinophils that damages nervecells in tissue culture and there is also evidence forneurotoxicity in the hypereosinophilic syndrome.8The development of a systemic Jarisch-Herxheimerreaction due to the abrupt dissolution of larvaecausing a marked release of protein breakdownproducts, is a further reason for exhibiting steroidsin the treatment of trichinosis.

Acknowledgements

We would like to thank Miss Agatha M.F. Mak for herhelp with preparing the manuscript, the Medical MediaServices of the Prince of Wales Hospital, The ChineseUniversity of Hong Kong for the illustrations and Dr lainM. Fairley for referring the case for CT. We would alsolike to thank Dr Ronald Ko, reader in parasitology at theHong Kong University, for the ELISA data on these twopatients.

References

1. Simon, J.W., Riddell, N.J., Wong, W.T., Au, A.C.S.,Ko, R.C. & Templer, M.J. Further observations onthe first documented outbreak of trichinosis in HongKong. Trans R Soc Trop Med Hyg 1986, 80:394-397.

2. Teplick, J.G. & Haskin, M.E. Roentgenologic Diag-nosis: A complement in radiology to the Beeson andMcDermott Textbook of Medicine, 3rd ed. W.B.Saunders, Philadelphia, 1976.

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3. DuBoulay, G.H. In A Textbook of Radiological Diag-nosis, vol. 1, 5th ed. H.K. Lewis, London, 1984.

4. Grainger, R.G. & Allison, D.J. Diagnostic Radiology.Anglo-American Textbook of Imaging. ChurchillLivingstone, London, Melbourne and New York,1986.

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6. Lee, H.S. & Rao, K.C.V.G. Cranial Computed Tomo-graphy and MRI, 2nd ed. McGraw-Hill, New York,1983.

7. Stevens, J.M., Valentine, A.R. & Kendall, B.E.Computed Cranial and Spinal Imaging. A PracticalIntroduction. William Heinemann Medical Books,London, 1988.

8. Ellrodt, A., Halfon, P., Le Bras, P. et al. MultifocalCNS lesions in three patients with trichinosis. ArchNeurol 1987, 44: 432-434.

9. Gay, T., Pankey, G.A. & Beckman, E.N. Fatal CNStrichinosis. JAMA 1982, 247: 1024-1025.

10. Gould, S.E. Trichinosis in Man and Animals. CharlesC. Thomas, Springfield, Illinois, 1970.

11. Delessio, D.J. & Wolff, H.G. Trichinella spiralisinfection of the C.N.S. Arch Neurol 1961, 4: 407-417.

12. Kramer, M.D. & Aita, J.F. Trichinosis. In: Vinken,P.J. & Bruyn, G.W. (eds) Handbook of ClinicalNeurology. Elsevier North-Holland, New York, 35,1978, pp. 267-290.

13. Davis, M.J., Cilo, M., Plaitakis, A. & Yahr, M.D.Trichinosis: severe myopathic involvement withrecovery. Neurology 1976, 26: 37-40.

14. Most, H. Trichinosis - preventable yet still with us. NEngl J Med 1978, 298: 1178-1180.

15. Leads from MMWR - 1, 3. Trichinosis - Maine,Alaska. JAMA 1986, 255: 177-180.

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