1992, The British Journal of Radiology, 65, 447-449
primary bronchogenic neoplasm, a primary nerve sheath tumour such as a malignant schwannoma or neurinoma, a parasellar meningioma and extension into the cavernous sinus from a pituitary adenoma. The histology of a seminoma metastasis at this site has been described previously and the similarity to that of a primary midline germinoma noted (Averback & Olivier, 1977). The treatment of metastatic seminoma with carboplatin results in an overall disease free survival rate of 80% (Horwich et al, 1989), most of the remaining 20% of patients being salvaged by further intensive chemotherapy. This allows the majority of patients to be treated with a simple regime that can usually be given on an out-patient basis. Most reports have suggested that r2-weighted sequences have a high specificity for differentiating between fibrosis and tumour, but more recent work has cast some doubt on this (Lee & Glazer, 1990). Short Tx inversion recovery sequences, emphasizing the effect of the prolonged T, and T2 values characteristically found in tumour, have also been used to try to differentiate between active tumour and fibrosis (Dwyer et al, 1988). In this case the persisting enhancement of the residual soft tissue mass 4 months after chemotherapy caused some difficulty in interpretation. It has been suggested that Gd-DTPA enhanced MRI may be of value in differentiating between tumour and fibrosis (Kassel et al, 1989). However, there have been reports of persistent enhancement in biopsy proven fibrosis at other sites even at 3 years (Werthmuller et al, 1989) and in the spine epidural fibrosis enhances following back surgery. Hence, persisting enhancement does not necessarily mean that there is active tumour present.
Acknowledgments We would like to acknowledge the help of Dr J. E. Husband, Professor A. Horwich and Dr D. P. Dearnaley in preparing this manuscript. References AVERBACK, P. & OLIVIER, A., 1977. Metastatic intracranial
seminoma. Archives of Neurology, 36, 40. BREDAEL, J. J., VUGRIN, D. & WHITMORE, W. F., 1982. Autopsy
findings in 154 patients with germ cell tumours of the testis. Cancer, 50, 548-551. DWYER, A. J., FRANK, J. A., SANK, V. J., REINIG, J. W.,
HICKEY, A. M. & DOPPMAN, J. L., 1988. Short-Tl inversion-
recovery pulse sequence: analysis and initial experience in cancer imaging. Radiology, 168, 827-836. HORWICH, A., DEARNALEY, D. P., DUCHESNE, G. M., WILLIAMS, M., BRADA, M. & PECKHAM, M. J., 1989. Simple
non-toxic treatment of seminoma with carboplatin. Journal of Clinical Oncology, 7, 1150-1156. HUSBAND,
J.
E.
&
BELLAMY,
E.
A.,
1985.
Unusual
thoracoabdominal sites of metastases in testicular tumours. American Journal of Roentgenology, 145, 1165-1171. KASSEL, E. A., KELLER, M. A. & KUCHARCZYK, W., 1989. MRI
of the floor of the mouth, tongue and orohypopharynx. Radiologic Clinics of North America, 27, 331-351. LEE, K. T. & GLAZER, H. S., 1990. Controversy in the MR
imaging appearance of fibrosis. Radiology, 177, 21-22. RUSH, J. A., OLDER, J. J. & RICHMAN, A. V., 1981. Testicular
seminoma metastatic to the orbit. American Journal of Ophthalmology, 91, 258-260. SAGALOWSKY, A. I., MCCONNELL, J. D. & ADMIRE, R., 1986.
Uncommon sites of recurrent seminoma and implications for therapy. Cancer, 57, 1060-1065. WERTHMULLER, W. C , SCHIEBLER, M. L., WHALEY, R. A., MAURO, M. A. & MCCARTNEY, W. H., 1989.
Gadolinium-DTPA enhancement of lung radiation fibrosis. Journal of Computer Assisted Tomography, 13, 946-948.
"Tc m HMPAO SPECT in progressive multifocal leucoencephalopathy By Dr J . V. Bowler, BSc, MRCP, Dr P. T. G. Davies, MA, MRCP and Dr G. D. Perkin, FRCP The Regional Neurosciences Centre, Charing Cross Hospital, Fulham Palace Road, London W6 8RF, UK
(Received 12 June 1991 and in revised form 19 September 1991, accepted 16 October 1991) Keywords: SPECT, Progressive multifocal leucoencephalopathy
Progressive multifocal leucoencephalopathy (PML), a rare condition caused by the JC papovavirus, is characterized by multiple areas of demyelination within the central nervous system. It almost always occurs in the context of immunosuppression and as a result of AIDS the number of cases has increased (Levy et al, 1988; Lang et al, 1989). Both computed tomography Address correspondence to Dr J. V. Bowler. Vol. 65, No. 773
(CT) scanning and magnetic resonance imaging (MRI) have been found to be of limited value in establishing the diagnosis of PML. An alternative technique that might support a clinical diagnosis of PML would therefore be valuable, particularly if it would avoid the need to proceed to biopsy. We report a case of biopsy proven PML investigated by single photon emission computerized tomography (SPECT) using "Tcm hexamethylpropyleneamineoxime ("Tcm HMPAO). This is the first 447
Case reports
Figure 2. SPECT done 7 days after the first CT showing much more extensive changes including the overlying cortex and thalamus.
Figure 1. CT scan showing low density changes, later proven to be PML, confined to white matter. report of regional cerebral blood flow (rCBF) imaging in PML. We suggest that the appearances may be sufficiently characteristic to be of diagnostic use. Case report A 62-year-old man was diagnosed as having chronic lymphatic leukaemia in 1982 and was treated with chlorambucil from 1986. 8 years after diagnosis he started to misjudge distances while driving and was involved in a road traffic accident. Examination in casualty revealed an incomplete right homonymous hemianopia. Over the next 4 weeks he developed right sided clumsiness progressing to an inability to stand unaided. On admission to hospital his right homonymous hemianopia had become complete and he had a right hemiparesis. A CT brain scan performed soon after admission showed extensive diminished density in the left parietal, lateral occipital and posterior temporal regions, without enhancement. There was some mass effect but no midline shift (Fig. 1). Full haematological and biochemical investigations, electrocardiogram, echocardiogram and chest radiograph showed no relevant abnormality. Cerebrospinal fluid examination showed no malignant cells, no white cells, a glucose of 4 mmol/1 and a protein of 0.37 g/1. SPECT showed an extensive area of white and grey matter perfusion deficits involving the left occipital cortex, lentiform nucleus and the anterior parietal lobe with its underlying white matter (Fig. 2). The uptake in these regions was compared with the contralateral side using standard regions of interest and was 1.08 for the cerebellum, 0.83 for the thalamus and 0.51 for the white matter of the occipital cortex, though in the heart of the lesion there was a substantial area with negligible uptake. Over the next 3 weeks there was a progressive neurological deterioration. He became apraxic, dyscalculic, dyslexic, hemiplegic and developed right/left and time and place disorientation. A repeat CT scan, 25 days after the first, showed no significant change. In view of his clinical 448
deterioration he underwent an open brain biopsy which confirmed PML. Discussion The CT abnormalities in our case were insufficient to account for the neurological deficit. This discrepancy, which also applies to MRI, has been observed previously (Ledoux et al, 1989) and has been suggested as a diagnostic clue (Krupp et al, 1985). The only previous study of PML by functional imaging was a positron emission tomogram utilizing fluorodeoxyglucose (Kiyosawa et al, 1988), which revealed extensive metabolic changes remote from the lesion consistent with diaschisis. The modest decrease in HMPAO uptake seen in the contralateral cerebellum and ipsilateral thalamus would be consistent with diaschisis, though there were no clinical correlates of this. However, because PML is multifocal the possibility that these changes were caused by separate lesions and not by diaschisis cannot be dismissed. The changes seen in the occipital cortical grey matter are relatively severe for diaschisis, but this area of cortex is typically thin on SPECT (see the opposite side) and the decrease seen here may be in part partial volume and part diaschisis, though grey matter involvement cannot be excluded. The changes seen on "Tc m HMPAO SPECT are much more consistent with the clinical picture than the CT findings. They suggest that rCBF changes secondary to demyelination and cystic change are more extensive than previously thought. Of particular interest are the grey matter changes. These are such rare and late features of PML imaged by CT scanning for their absence to be used diagnostically (Levy & Bredesen, 1988; Ledoux et al, 1989). Whether they can all be explained by diaschisis or whether there is some direct involvement of grey matter, perhaps of fibre tracts within predominantly grey matter, remains speculative. The British Journal of Radiology, May 1992
1992, The British Journal of Radiology, 65, 449-451 The pattern of the changes in HMPAO uptake demonstrated by SPECT were unique in this case. It is distinct in appearance from the changes of leukoariosis in that it is focal and relatively remote from the ventricles. It is distinguished from posterior cerebral artery lesions not only by its relative sparing of the medial occipital and inferior occipitotemporal cortex, but also by its prominent involvement of white matter and its extension forward into middle cerebral artery territory. Whilst the CT appearances might be mistaken for vasogenic oedema, the profound fall in HMPAO uptake demonstrates that it is not oedema alone. This, in combination with the close correlation with the clinical deficit, suggests that HMPAO SPECT may, in conjunction with CT or MRI, be of value in the diagnosis of PML. This observation may be of increasing importance as SPECT is readily available and the incidence of PML is expected to increase due to AIDS. Further examples in biopsy proven cases will be required.
LEVY, R. M., JANSSEN, R. S., BUSH, T. J. & ROSENBLUM, M. L.,
References KIYOSAWA, M., BOSLEY, T. M., ALAvi, A., GUPTA, N., RHODES,
1988. Neuroepidemiology of acquired immunodeficiency syndrome. Journal of Acquired Immune Deficiency Syndrome, 1, 31-40.
R. C , SCHATZ, N. J., REIVICH, M. & JAMIESON, D., 1988.
Positron emission tomography in a patient with progressive multifocal leukoencephalopathy. Neurology, 38, 1864-1867. KRUPP, L. B., LIPTON, R. B., SWERDLOW, M. L., LEEDS, N. E.
& LLENA, J., 1985. Progressive multifocal leukoencephalopathy: clinical and radiographic features. Annals of Neurology, 17, 344-349. LANG, W., MIKLOSSY, J., DERUAZ, J. P., PIZZOLATO, G. P., PROBST, A., SCHAFFNER, T., GESSAGA, E. & KLEIHUES, P.,
1989. Neuropathology of the acquired immune deficiency syndrome (AIDS): a report of 135 consecutive autopsy cases from Switzerland. Ada Neuropathologica (Berlin), 77, 379-390. LEDOUX,
S.,
LIBMAN, I.,
ROBERT,
F.
& JUST,
N.,
1989.
Progressive multifocal leukocephalopathy with gray matter involvement. Canadian Journal of Neurological Sciences, 16, 200-202. LEVY, R. M. & BREDESEN, D. E., 1988. Central nervous system dysfunction in acquired immunodeficiency syndrome. Journal of Acquired Immune Deficiency Syndrome, 1, 41-64.
C. H., CHAWLUK, J., KUSHNER, M., SAVINO, P. J., SERGOTT,
Increased attenuation value of a colloid cyst of the third ventricle following ventricular decompression By N. G. Warnock, MRCP ( U K ) , FRCR and T. Powell, FRCP, FRCR Department of Diagnostic Radiology, Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF, UK
{Received 8 August 1991, accepted 3 October 1991) Keywords: Colloid cyst, Computed tomography
Case report A 35-year-old woman presented with a 3 month history of postural unsteadiness. She complained of worsening headaches, with blurred vision for 1 week, accompanied by nausea and vomiting. On examination she was found to have bilateral papilloedema, with slight slowness of mentation but no other feature. Axial computed tomography (CT) (Fig. 1) showed gross dilatation of the lateral ventricles, with a collapsed third ventricle, consistent with the presence of obstruction to cerebrospinal fluid (CSF) flow at the foramina of Munro. No mass was seen. A ventriculo-peritoneal shunt was inserted into the right lateral ventricle, with relief of symptoms. A repeat CT at 4 days after shunting showed collapse of the right lateral ventricle, with a considerable reduction in the size of the left (Fig. 2). Cerebral angiography was performed and was normal. When reviewed 6 weeks later, she had some recurrence of headaches and complained of pain in the right flank. Cranial CT (Fig. 3) showed that ventricles were unchanged, but that a rounded hyperdense mass had appeared in the anterior end of Vol. 65, No. 773
the third ventricle typical of a colloid cyst. Persisting flank pain was thought to be due to irritation by the shunt, which was therefore removed. A further scan 1 week later again showed the colloid cyst which appeared to have enlarged slightly (Fig. 4). The ventricles had increased in size and accordingly excision of the cyst was performed. The patient was discharged in good health after 1 week and remains well 1 year later. Pathological examination of the specimen showed a typical colloid cyst containing amorphous eosinophilic material. Discussion The typical appearance of a colloid cyst of the third ventricle is a rounded hyperdense mass in the anterior end of the third ventricle in the plane of the foramina of Munro (Ganti et al, 1981). Infrequently isodense and hypodense cysts are encountered; they may be difficult to detect on CT. Contrast enhancement is reported (Zilkha, 1981; Hine & Chui, 1987), but in none of the reported cases are the measurement details sufficiently precise to judge the possible contribution of technical
449
primary bronchogenic neoplasm, a primary nerve sheath tumour such as a malignant schwannoma or neurinoma, a parasellar meningioma and extension into the cavernous sinus from a pituitary adenoma. The histology of a seminoma metastasis at this site has been described previously and the similarity to that of a primary midline germinoma noted (Averback & Olivier, 1977). The treatment of metastatic seminoma with carboplatin results in an overall disease free survival rate of 80% (Horwich et al, 1989), most of the remaining 20% of patients being salvaged by further intensive chemotherapy. This allows the majority of patients to be treated with a simple regime that can usually be given on an out-patient basis. Most reports have suggested that r2-weighted sequences have a high specificity for differentiating between fibrosis and tumour, but more recent work has cast some doubt on this (Lee & Glazer, 1990). Short Tx inversion recovery sequences, emphasizing the effect of the prolonged T, and T2 values characteristically found in tumour, have also been used to try to differentiate between active tumour and fibrosis (Dwyer et al, 1988). In this case the persisting enhancement of the residual soft tissue mass 4 months after chemotherapy caused some difficulty in interpretation. It has been suggested that Gd-DTPA enhanced MRI may be of value in differentiating between tumour and fibrosis (Kassel et al, 1989). However, there have been reports of persistent enhancement in biopsy proven fibrosis at other sites even at 3 years (Werthmuller et al, 1989) and in the spine epidural fibrosis enhances following back surgery. Hence, persisting enhancement does not necessarily mean that there is active tumour present.
Acknowledgments We would like to acknowledge the help of Dr J. E. Husband, Professor A. Horwich and Dr D. P. Dearnaley in preparing this manuscript. References AVERBACK, P. & OLIVIER, A., 1977. Metastatic intracranial
seminoma. Archives of Neurology, 36, 40. BREDAEL, J. J., VUGRIN, D. & WHITMORE, W. F., 1982. Autopsy
findings in 154 patients with germ cell tumours of the testis. Cancer, 50, 548-551. DWYER, A. J., FRANK, J. A., SANK, V. J., REINIG, J. W.,
HICKEY, A. M. & DOPPMAN, J. L., 1988. Short-Tl inversion-
recovery pulse sequence: analysis and initial experience in cancer imaging. Radiology, 168, 827-836. HORWICH, A., DEARNALEY, D. P., DUCHESNE, G. M., WILLIAMS, M., BRADA, M. & PECKHAM, M. J., 1989. Simple
non-toxic treatment of seminoma with carboplatin. Journal of Clinical Oncology, 7, 1150-1156. HUSBAND,
J.
E.
&
BELLAMY,
E.
A.,
1985.
Unusual
thoracoabdominal sites of metastases in testicular tumours. American Journal of Roentgenology, 145, 1165-1171. KASSEL, E. A., KELLER, M. A. & KUCHARCZYK, W., 1989. MRI
of the floor of the mouth, tongue and orohypopharynx. Radiologic Clinics of North America, 27, 331-351. LEE, K. T. & GLAZER, H. S., 1990. Controversy in the MR
imaging appearance of fibrosis. Radiology, 177, 21-22. RUSH, J. A., OLDER, J. J. & RICHMAN, A. V., 1981. Testicular
seminoma metastatic to the orbit. American Journal of Ophthalmology, 91, 258-260. SAGALOWSKY, A. I., MCCONNELL, J. D. & ADMIRE, R., 1986.
Uncommon sites of recurrent seminoma and implications for therapy. Cancer, 57, 1060-1065. WERTHMULLER, W. C , SCHIEBLER, M. L., WHALEY, R. A., MAURO, M. A. & MCCARTNEY, W. H., 1989.
Gadolinium-DTPA enhancement of lung radiation fibrosis. Journal of Computer Assisted Tomography, 13, 946-948.
"Tc m HMPAO SPECT in progressive multifocal leucoencephalopathy By Dr J . V. Bowler, BSc, MRCP, Dr P. T. G. Davies, MA, MRCP and Dr G. D. Perkin, FRCP The Regional Neurosciences Centre, Charing Cross Hospital, Fulham Palace Road, London W6 8RF, UK
(Received 12 June 1991 and in revised form 19 September 1991, accepted 16 October 1991) Keywords: SPECT, Progressive multifocal leucoencephalopathy
Progressive multifocal leucoencephalopathy (PML), a rare condition caused by the JC papovavirus, is characterized by multiple areas of demyelination within the central nervous system. It almost always occurs in the context of immunosuppression and as a result of AIDS the number of cases has increased (Levy et al, 1988; Lang et al, 1989). Both computed tomography Address correspondence to Dr J. V. Bowler. Vol. 65, No. 773
(CT) scanning and magnetic resonance imaging (MRI) have been found to be of limited value in establishing the diagnosis of PML. An alternative technique that might support a clinical diagnosis of PML would therefore be valuable, particularly if it would avoid the need to proceed to biopsy. We report a case of biopsy proven PML investigated by single photon emission computerized tomography (SPECT) using "Tcm hexamethylpropyleneamineoxime ("Tcm HMPAO). This is the first 447
Case reports
Figure 2. SPECT done 7 days after the first CT showing much more extensive changes including the overlying cortex and thalamus.
Figure 1. CT scan showing low density changes, later proven to be PML, confined to white matter. report of regional cerebral blood flow (rCBF) imaging in PML. We suggest that the appearances may be sufficiently characteristic to be of diagnostic use. Case report A 62-year-old man was diagnosed as having chronic lymphatic leukaemia in 1982 and was treated with chlorambucil from 1986. 8 years after diagnosis he started to misjudge distances while driving and was involved in a road traffic accident. Examination in casualty revealed an incomplete right homonymous hemianopia. Over the next 4 weeks he developed right sided clumsiness progressing to an inability to stand unaided. On admission to hospital his right homonymous hemianopia had become complete and he had a right hemiparesis. A CT brain scan performed soon after admission showed extensive diminished density in the left parietal, lateral occipital and posterior temporal regions, without enhancement. There was some mass effect but no midline shift (Fig. 1). Full haematological and biochemical investigations, electrocardiogram, echocardiogram and chest radiograph showed no relevant abnormality. Cerebrospinal fluid examination showed no malignant cells, no white cells, a glucose of 4 mmol/1 and a protein of 0.37 g/1. SPECT showed an extensive area of white and grey matter perfusion deficits involving the left occipital cortex, lentiform nucleus and the anterior parietal lobe with its underlying white matter (Fig. 2). The uptake in these regions was compared with the contralateral side using standard regions of interest and was 1.08 for the cerebellum, 0.83 for the thalamus and 0.51 for the white matter of the occipital cortex, though in the heart of the lesion there was a substantial area with negligible uptake. Over the next 3 weeks there was a progressive neurological deterioration. He became apraxic, dyscalculic, dyslexic, hemiplegic and developed right/left and time and place disorientation. A repeat CT scan, 25 days after the first, showed no significant change. In view of his clinical 448
deterioration he underwent an open brain biopsy which confirmed PML. Discussion The CT abnormalities in our case were insufficient to account for the neurological deficit. This discrepancy, which also applies to MRI, has been observed previously (Ledoux et al, 1989) and has been suggested as a diagnostic clue (Krupp et al, 1985). The only previous study of PML by functional imaging was a positron emission tomogram utilizing fluorodeoxyglucose (Kiyosawa et al, 1988), which revealed extensive metabolic changes remote from the lesion consistent with diaschisis. The modest decrease in HMPAO uptake seen in the contralateral cerebellum and ipsilateral thalamus would be consistent with diaschisis, though there were no clinical correlates of this. However, because PML is multifocal the possibility that these changes were caused by separate lesions and not by diaschisis cannot be dismissed. The changes seen in the occipital cortical grey matter are relatively severe for diaschisis, but this area of cortex is typically thin on SPECT (see the opposite side) and the decrease seen here may be in part partial volume and part diaschisis, though grey matter involvement cannot be excluded. The changes seen on "Tc m HMPAO SPECT are much more consistent with the clinical picture than the CT findings. They suggest that rCBF changes secondary to demyelination and cystic change are more extensive than previously thought. Of particular interest are the grey matter changes. These are such rare and late features of PML imaged by CT scanning for their absence to be used diagnostically (Levy & Bredesen, 1988; Ledoux et al, 1989). Whether they can all be explained by diaschisis or whether there is some direct involvement of grey matter, perhaps of fibre tracts within predominantly grey matter, remains speculative. The British Journal of Radiology, May 1992
1992, The British Journal of Radiology, 65, 449-451 The pattern of the changes in HMPAO uptake demonstrated by SPECT were unique in this case. It is distinct in appearance from the changes of leukoariosis in that it is focal and relatively remote from the ventricles. It is distinguished from posterior cerebral artery lesions not only by its relative sparing of the medial occipital and inferior occipitotemporal cortex, but also by its prominent involvement of white matter and its extension forward into middle cerebral artery territory. Whilst the CT appearances might be mistaken for vasogenic oedema, the profound fall in HMPAO uptake demonstrates that it is not oedema alone. This, in combination with the close correlation with the clinical deficit, suggests that HMPAO SPECT may, in conjunction with CT or MRI, be of value in the diagnosis of PML. This observation may be of increasing importance as SPECT is readily available and the incidence of PML is expected to increase due to AIDS. Further examples in biopsy proven cases will be required.
LEVY, R. M., JANSSEN, R. S., BUSH, T. J. & ROSENBLUM, M. L.,
References KIYOSAWA, M., BOSLEY, T. M., ALAvi, A., GUPTA, N., RHODES,
1988. Neuroepidemiology of acquired immunodeficiency syndrome. Journal of Acquired Immune Deficiency Syndrome, 1, 31-40.
R. C , SCHATZ, N. J., REIVICH, M. & JAMIESON, D., 1988.
Positron emission tomography in a patient with progressive multifocal leukoencephalopathy. Neurology, 38, 1864-1867. KRUPP, L. B., LIPTON, R. B., SWERDLOW, M. L., LEEDS, N. E.
& LLENA, J., 1985. Progressive multifocal leukoencephalopathy: clinical and radiographic features. Annals of Neurology, 17, 344-349. LANG, W., MIKLOSSY, J., DERUAZ, J. P., PIZZOLATO, G. P., PROBST, A., SCHAFFNER, T., GESSAGA, E. & KLEIHUES, P.,
1989. Neuropathology of the acquired immune deficiency syndrome (AIDS): a report of 135 consecutive autopsy cases from Switzerland. Ada Neuropathologica (Berlin), 77, 379-390. LEDOUX,
S.,
LIBMAN, I.,
ROBERT,
F.
& JUST,
N.,
1989.
Progressive multifocal leukocephalopathy with gray matter involvement. Canadian Journal of Neurological Sciences, 16, 200-202. LEVY, R. M. & BREDESEN, D. E., 1988. Central nervous system dysfunction in acquired immunodeficiency syndrome. Journal of Acquired Immune Deficiency Syndrome, 1, 41-64.
C. H., CHAWLUK, J., KUSHNER, M., SAVINO, P. J., SERGOTT,
Increased attenuation value of a colloid cyst of the third ventricle following ventricular decompression By N. G. Warnock, MRCP ( U K ) , FRCR and T. Powell, FRCP, FRCR Department of Diagnostic Radiology, Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF, UK
{Received 8 August 1991, accepted 3 October 1991) Keywords: Colloid cyst, Computed tomography
Case report A 35-year-old woman presented with a 3 month history of postural unsteadiness. She complained of worsening headaches, with blurred vision for 1 week, accompanied by nausea and vomiting. On examination she was found to have bilateral papilloedema, with slight slowness of mentation but no other feature. Axial computed tomography (CT) (Fig. 1) showed gross dilatation of the lateral ventricles, with a collapsed third ventricle, consistent with the presence of obstruction to cerebrospinal fluid (CSF) flow at the foramina of Munro. No mass was seen. A ventriculo-peritoneal shunt was inserted into the right lateral ventricle, with relief of symptoms. A repeat CT at 4 days after shunting showed collapse of the right lateral ventricle, with a considerable reduction in the size of the left (Fig. 2). Cerebral angiography was performed and was normal. When reviewed 6 weeks later, she had some recurrence of headaches and complained of pain in the right flank. Cranial CT (Fig. 3) showed that ventricles were unchanged, but that a rounded hyperdense mass had appeared in the anterior end of Vol. 65, No. 773
the third ventricle typical of a colloid cyst. Persisting flank pain was thought to be due to irritation by the shunt, which was therefore removed. A further scan 1 week later again showed the colloid cyst which appeared to have enlarged slightly (Fig. 4). The ventricles had increased in size and accordingly excision of the cyst was performed. The patient was discharged in good health after 1 week and remains well 1 year later. Pathological examination of the specimen showed a typical colloid cyst containing amorphous eosinophilic material. Discussion The typical appearance of a colloid cyst of the third ventricle is a rounded hyperdense mass in the anterior end of the third ventricle in the plane of the foramina of Munro (Ganti et al, 1981). Infrequently isodense and hypodense cysts are encountered; they may be difficult to detect on CT. Contrast enhancement is reported (Zilkha, 1981; Hine & Chui, 1987), but in none of the reported cases are the measurement details sufficiently precise to judge the possible contribution of technical
449
