British Journal of Radiology 74 (2001),83-85 © 2001 The British Institute of Radiology
Cerebral cryptococcosis: atypical appearances on CT
M Awasthi, MBBS
1
T Patankar, MD
1
P Shah, MD
1 and
M Castillo, MD
2
1 Department of Radiology, King Edward VII Memorial Hospital, Acharya Donde Marg, Parel, Bombay, India
2 Department of Radiology, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7510, USA
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Abstract
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Cryptococccal infection is common in immunocompromised patients, often presenting with meningitis or meningoencephalitis. We report an unusual presentation of cryptococcal infection in an immunocompetent patient presenting with headache and hemiplegia. CT demonstrated a large ring-enhancing lesion in the parietal region with intralesional calcification.
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Introduction
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Cryptococcosis is the most common fungal infection of the central nervous system [1, 2]. Most patients present with signs of meningitis and less frequently meningoencephalitis [3–7]. Both parenchymal and meningeal forms have been described [3–6]. Most reports describe cryptococcosis in immunocompromised patients [3–6]. We report a case of Cryptococcus neoformans infection in an immunocompetent patient with an atypical presentation of headache and gradual onset hemiparesis. CT demonstrated a large ring-enhancing lesion with calcification.
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Case report
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A 20-year-old man presented with right-sided headache and vomiting for 6 months. He gave history of pulmonary tuberculosis, which had been treated 5 years previously. On examination, the patient was afebrile and had no papilloedema or focal neurological deficit. Contrast enhanced CT showed a sharply marginated loculated lesion with rim enhancement in the upper right parietal region. There were multiple intralesional calcifications with minimal perilesional vasogenic oedema. No meningeal enhancement was seen. A provisional diagnosis of tuberculoma was considered and the patient was started on antituberculous chemotherapy. He showed no clinical improvement and presented 3 months later with gradual onset of left hemiparesis over a period of 1 month. He also had multiple episodes of generalized tonic and clonic convulsions. On clinical examination, decreased strength was found in the left arm and leg. Sensation was decreased on the left side. No clinical signs of meningeal irritation were observed. Fundoscopy showed papilloedema. Standard laboratory tests were normal. Tests for HIV were negative. ELISA test for toxoplasmosis was also negative. Repeat contrast enhanced CT showed that the lesion had significantly increased in size (Figures 1a
,b). There was mass effect with compression of the right lateral ventricle and subfalcine herniation to the left.
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Figure 1. (a) Contrast enhanced CT shows a sharply marginated, irregular, conglomerate, rim-enhancing lesion in the right high parietal cortex, 5 cm in its largest diameter. Surrounding vasogenic oedema is present. (b) A higher section shows intralesional calcification.
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A stereotactic biopsy showed multiple refractile yeast forms with a surrounding halo, amidst tissue showing moderate inflammation composed of a few lymphocytes and occasional neutrophils. The appearances were typical of cryptococcoma. The patient was treated with Amphotericin B, anticonvulsants and intravenous steroids. He made agradual recovery over 2 months. Strength improved considerably in the legs but the seizures persisted. Contrast enhanced CT 2 months later showed that the lesion had decreased in size with complete resolution of the surrounding oedema (Figure 2).
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Figure 2. Contrast enhanced CT 2 months after treatment with Amphotericin B shows resolution of oedema, although ring enhancement is persists.
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Discussion
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Cryptococcosis is caused by Cryptococcus neoformans, an encapsulated yeast-like fungus. It is a ubiquitous organism found in mammal and bird faeces, particularly in pigeon droppings [5, 7, 8]. Cryptococcosis is the most common mycotic infection involving the central nervous system (CNS) [1].Although it can affect immunocompetent patients, patients having an underlying chronic illness such as diabetes mellitus, collagen vascular disease, chronic renal disease, alcoholism, malignancy or those on immunosuppressive drugs are more susceptible to cryptococcosis [2, 7, 8]. It ranks third after HIV and Toxoplasma gondii among the infectious agents causing CNS disease in AIDS, affecting nearly 5% of HIV positive patients [1, 2].
The lung is the primary site of cryptococcal infection, with subsequent spread to different organs via the haematogenous route. CNS cryptococcosis has two forms: meningeal and parenchymal. Meningitis is often the primary manifestation and is most pronounced at the base of the brain. Hydrocephalus often develops as a result of meningeal scarring [5, 8]. No such evidence was seen either clinically or on imaging in our patient. Parenchymal involvement in cryptococcosis may be in the form of parenchymal cryptococcomas or torulomas, dilated Virchow Robin spaces (pseudocysts), multiple enhancing cortical nodules and a mixed variety [4].
It is believed that meningeal spread through subarachnoid and perivascular spaces or ventricles may be the source of parenchymal invasion of cryptococcii [2, 3]. The commonest parenchymal sites are the midbrain and the basal ganglia [4]. A collection of organisms, inflammatory cells and gelatinous mucoid material forms a cryptococcoma [2]. A cryptococcoma may be focal homogeneous nodules with or without circumferential oedema or may rarely exhibit ring-like contrast enhancement [4, 9]. Contrast enhancement of cryptococcomas or meninges is rare because of underlying immunosuppression in most patients or the non-immunogenic nature of the polysaccharide capsule of the cryptococcal organism [1]. Infection spreading along the Virchow Robin spaces that accompany the perforating arteries forms gelatinous pseudocysts, or so called "soap bubbles" [2, 4]. They appear as fluid-filled cysts mainly in the basal ganglia, thalamus, substantia nigra and periventricular regions [2, 4]. On MRI they are typically non-enhancing hypointense lesions on T1 weighted images and hyperintense lesions on T2 weighted images [2]. Brain stem compression requiring surgical decompression has been due to large cryptococcal cysts formed by the coalescence of small cysts [7].
CNS cryptococcosis commonly presents with manifestations of meningitis and encephalitis such as headache, nausea, staggering gait, dementia, irritability, confusion and blurred vision. Both fever and nuchal rigidity are mild or absent [2, 7]. The course may be fulminant or chronic and insidious. Lumbar puncture is the single most useful laboratory investigation. CSF pressure is often raised and may show mild to moderate leucocytosis, decreased glucose and elevated protein levels [7, 8]. India ink smears demonstrate the yeast. Elevated cryptococcal antigen may be found in the serum or CSF [2, 5, 7].
The differential diagnosis on imaging includes infectious causes such as toxoplasmosis, cytomegalovirus, tuberculoma, pyogenic abcess as well as lymphoma and metastatic disease.
The clinical picture in our patient was unusual, with an insidious onset and no evidence of meningitis. Although parenchymal cryptococcomas are well described, such a large rim-enhancing cryptococcoma has not been reported. The high parietal lobe is an unusual site for CNS cryptococcosis, the usual sites being basal ganglia and the midbrain. Such a large lesion occurring in an immunocompetent individual is rare in CNS cryptococcosis. The ring enhancement was possibly due to the patient's ability to mount an immune response, which would be uncommon in immunosuppressed patients. Another notable feature is the multiple foci of calcification within the lesion. Such parenchymal calcification in cryptococcosis is rare [7] and may be attributed to the protracted course of the disease in this patient.
Cryptococcosis is usually treated with intravenous Amphotericin B [3, 10]. Surgical drainage of large pseudocysts has been reported [7, 10]. Surgical removal of the cryptococcoma was performed in this patient as his convulsions were not responding to drug therapy.
In conclusion, cryptococcosis may be considered in the differential diagnosis in immunocompetent patients with atypical clinical presentation and intracranial rim-enhancing lesions, even in the presence of intralesional calcification.
Received for publication July 26, 2000.
Revision received September 20, 2000.
Accepted for publication October 5, 2000.
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Abstract
Introduction
