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Isolated cerebellar metastasis from carcinoma of the colon

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A 58-year-old man presented with a history of altered sensorium for 15 days. There was a history of generalised weakness, mild anorexia and malaise for 3 months. There was no history of fever, headache, vomiting, convulsions, head injury, pain in the abdomen, altered bowel habits, or gastrointestinal bleeding. The patient was a non-smoker and did not consume alcohol.

On general physical examination, he was in a state of altered sensorium and was not responding to verbal commands. He was dehydrated and had pallor. There was no discernible focal neurological deficit. His pupils were of normal size and were reacting to light. The fundus examination showed bilateral mild papilloedema. His cardiovascular, chest and abdominal examination was normal. On investigation, his haemoglobin was 8 g/dl, erythrocyte sedimentation rate was 52 mm for first hour, and peripheral smear showed microcytic hypochromic red blood cells. His blood sugar was 96 mg/dl, urea was 34 mg/dl, serum sodium was 149 mmol/l and serum potassium was 4.2 mmol/l. His liver function tests were normal. He was given intravenous fluids to correct dehydration and electrolyte imbalance. In spite of adequate hydration and normalisation of serum electrolytes, his sensorium did not improve, so he was subjected to a computed tomography (CT) scan of the head which showed a large space-occupying lesion in the left cerebellar hemisphere with hydrocephalus due to pressure effect on the fourth ventricle (figure). He underwent surgery for the cerebellar tumour the next day. The tumour was completely excised through a left-sided suboccipital craniectomy in prone position. Following the operation, his sensorium improved and he became fully conscious and oriented. The histopathology of the tumour showed a mucin-secreting adenocarcinoma which suggested that this was most probably a metastatic deposit. During investigations to find the primary site, colonoscopy showed an ulcerated growth at the hepatic flexure, a biopsy from which was suggestive of an adenocarcinoma. There was no colonic polyp. Ultrasonography of the abdomen did not show any metastasis to the liver or peritoneum. Chest X-ray was normal. The patient underwent right hemicolectomy. A cholecystectomy was also done for incidentally detected asymptomatic gall stones. Peroperatively, no metastases to liver, peritoneum or any other site were noted. The patient is presently doing well on adjuvant chemotherapy and intracranial irradiation.

Figure CT scan of the brain

Questions

1
What is the differential diagnosis of the space-occupying lesion seen in the figure?
2
What are the neoplastic diseases of the colon which can affect the cerebellum and in what way?

Answers

QUESTION 1

The differential diagnosis of solitary unilateral space-occupying lesion in the cerebellum is malignant astrocytoma, haemangioblastoma, metastatic lesion, or a rare tumour.

QUESTION 2

Cerebellar involvement in colonic neoplastic diseases can occur in three ways: (a) cerebellar degeneration as part of a paraneoplastic syndrome in a patient with colonic cancer, (b) in patients with familial colonic polyposis with malignant brain tumours described as Turcot's syndrome, and (c) metastatic deposit from colonic cancer.

Discussion

Carcinoma of the colon usually presents with bowel symptoms, anaemia and constitutional features such as anorexia and weight loss. Carcinoma of the colon may metastasise to distant organs such as liver and lung.1 Brain metastases are uncommon and have usually been reported in association with metastases to other organs, particularly lungs.2 Isolated brain metastases have been reported in patients with known carcinoma of the colon, the most common site being the cerebrum.2-4

Space-occupying lesions in the cerebellum include neoplastic lesions and abscess. Among the neoplastic lesions, the common tumours are medulloblastoma, astrocytoma (usually cystic), haemangioblastoma, meningioma, and others which include metastatic lesions, ependymoma, choroid plexus papillomas, and hamartoma. Of these, medulloblastoma most commonly affects children while astrocytoma and haemangioblastoma may occur in adults. In a series of 290 patients with cerebellar tumours, Biemond found medulloblastoma in 31%, cystic astrocytoma in 23%, haemangio-endothelioma in 18% and others in 28% of cases.5

Brain metastases discovered before the diagnosis of primary colonic cancer have been described,4 6 7 but we could find no cases of isolated cerebellar metastasis without metastases to other organs in a patient with previously undiagnosed carcinoma of the colon after searching through MEDLAR from 1966 to 97.

Metastases to brain most commonly occur by a haematogenous route via the portal venous system through the liver, heart, lungs and finally the carotids. Because of this route most cases of carcinoma of the colon present with liver metastasis before involvement of other organs. In the present case, however, there was cerebellar metastasis without any metastases to the liver or lungs. Ishikuraet al reported 11 cases with metastatic brain tumours without metastasis to liver or lungs.8However, their patients did not have cerebellar metastasis and were diagnosed cases of colorectal cancers. Micrometastases are well known in patients with carcinoma of the colon and there is a possibility that our patient also might be harbouring micrometastases.

Learning points

  • most cerebellar tumours are primary, the commonest being medulloblastoma

  • metastases to the cerebellum are uncommon

  • isolated cerebellar metastasis from carcinoma of the colon may occur

  • the diagnosis of primary neoplasm may follow the diagnosis of metastatic cerebellar involvement

  • surgical excision of the cerebellar tumour, whether primary or metastatic, is the treatment of choice

Cerebellar involvement may also occur as cerebellar degeneration in patients with carcinoma of the colon. Cerebellar degeneration has been reported as a paraneoplastic syndrome, mainly in patients with gynaecological malignancies, and is associated with anti-Yo antibodies.9 Although uncommon, cerebellar degeneration has been reported in patients with carcinoma of the colon.10 It has been shown that PCA-AA protein, which is responsible for cerebellar degeneration, may be expressed by colonic tumours.11

Cerebellar tumours may be present in association with adenoma/adenocarcinoma of the colon in patients with Turcot's syndrome.12 However, in Turcot's syndrome the histology of the brain tumour is different from that of colonic tumour and is not adenoma or adenocarcinoma. The present case did not have any colonic polyps and the histology of the cerebellar and the colonic tumours were similar, ie, adenocarcinoma. Thus, this patient obviously did not have Turcot's syndrome.

Final diagnosis

Isolated cerebellar metastasis from a previously undiagnosed carcinoma of the colon.

References

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