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Original Report |
1
Department of Radiology, Massachusetts General Hospital, 55 Fruit St., Gray
Building 2nd Floor, Boston, MA 02114.
2
Present address: Department of Radiology, New York—Presbyterian
Hospital, NewYork Weill Cornell Medical Center, 520 E. 70th St., Starr
Pavilion—Starr 630, New York, NY 10021.
Received May 21, 2001;
accepted after revision June 25, 2001.
Address correspondence to P. C. Sanelli.
Abstract
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CONCLUSION. Contrast-enhanced T1-weighted MR images in all three patients with CNS schistosomiasis revealed a central linear enhancement surrounded by multiple enhancing punctate nodules, forming an "arborized" appearance. Pathologically, this enhancement pattern correlated with a host granulomatous response to Schistosoma species ova. Although the pattern is not present in all cases of CNS schistosomiasis, when it is observed, a diagnosis of CNS schistosomiasis should be considered.
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In this paper, we report the unique MR imaging findings associated with three cases of pathologically confirmed central nervous system (CNS) schistosomiasis. Although not observed in all patients with CNS schistosomiasis [3], we believe that the linear and nodular enhancement pattern we describe, when present, is strongly suggestive of this infection. Moreover, on the basis of an extensive review of the literature and our combined clinical experience, we believe that the enhancement pattern we describe has not previously been noted in other CNS worm infections or disease processes. We therefore suggest that this unique "arborized" appearance of the linear and nodular enhancement pattern may constitute a new sign for the diagnosis of CNS schistosomiasis.
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Laboratory studies were performed on only two patients, one with spinal involvement and one with cerebral involvement. In both patients, serum analysis showed no evidence of eosinophilia, and multiple stool samples were negative for Schistosoma species ova.
Imaging Findings
Initial MR imaging findings in the woman with spinal involvement revealed
diffuse T2-signal prolongation with expansion of the distal spinal cord and
conus medullaris (Fig. 1A).
Contrast-enhanced T1-weighted images showed central linear enhancement
surrounded by multiple enhancing punctate nodules, which gave the enhancement
pattern a clustered appearance (Fig.
1B).
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The MR images from the 30-year-old man with cerebral involvement showed left temporal lobe vasogenic edema with associated sulcal effacement and mass effect on the cerebral peduncle (Fig. 2A). Contrast-enhanced images showed multiple enhancing, closely spaced, punctate nodules, each measuring 1-2 mm (Fig. 2B). The nodules surrounded the central linear enhancement and formed a masslike structure with an arborized appearance. This enhancement pattern was confirmed on different imaging planes (Fig. 2C).
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Initial contrast-enhanced MR images of the 32-year-old man with cerebral involvement revealed central linear enhancement surrounded by multiple enhancing punctate nodules in the right anterior parietal lobe (Fig. 3A). This enhancement pattern also was confirmed on different imaging planes (Fig. 3B). On T2-weighted images, the mass was hyperintense with surrounding vasogenic edema (Fig. 3C). Because these MR imaging findings resembled those observed in the two other patients, we were able to make a prospective diagnosis of CNS schistosomiasis.
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Pathologic Diagnosis, Treatment, and Clinical Outcome
Rectal biopsy in the 41-year-old woman with spinal involvement revealed
well-formed, non-caseating granulomata with acid-fast structures that were
diagnosed as Schistosoma species ova. The granulomatous reaction and
tissue necrosis, however, caused distortion of the egg-shells, making precise
pathologic identification of the schistosomal species impossible. Stereotactic
brain biopsies of the left temporal and right parietal enhancing lesions in
the two patients with cerebral involvement revealed chronic granulomatous
inflammation containing refractile ovoid structures with broad lateral spines
that were diagnosed as Schistosoma mansoni. No adult worms were seen
in either biopsy specimen. All three patients were treated medically with
praziquantel and corticosteroid therapy. The patient with spinal involvement
was readmitted approximately 2 months after treatment with severe lower back
pain and bilateral lower extremity paresis. This patient received an
additional course of praziquantel and corticosteroid therapy. Follow-up MR
images showed complete resolution of the enhancing structure and edema,
although residual lower extremity sensory and motor deficits persisted. At
follow-up, the two patients with cerebral involvement were found to have had
complete resolution of their initial clinical symptoms and imaging
findings.
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Two main theories have been advanced to explain how Schistosoma species ova reach the CNS. The first theory postulates that the ova are carried to the CNS through arterial or retrograde venous blood flow and thus may be deposited anywhere along the path of the blood flow. This explanation would account for the sparse and scattered distribution of ova in the brain in patients with hepatosplenic schistosomal infection [6]. The other theory proposes that the ova are deposited in situ after the anomalous migration of adult worms during the initial or subacute stages of schistosomal infection [7]. This theory is supported by the occasional finding of adult worms within the leptomeningeal veins, and the confined area of ova deposition seen with the tumoral form of schistosomiasis.
CT findings of cerebral schistosomiasis have been described as single or multiple hyperdense lesions with variable enhancement surrounded by low-density edema with an associated mass effect [8]. Previous case reports of the MR imaging findings associated with CNS schistosomiasis have described a similar variable enhancement pattern, using such terms as diffuse, spotty, or nodular [9,10,11]. In these reports, the published images show a nodular enhancement pattern similar to that seen in our patients. In none of these reports was a central linear enhancing component mentioned nor was such enhancement observed in the published images [9,10,11].
Ours were the only schistosomiasis patients who underwent MR imaging at our institution during the last 15 years. On the images of each of these patients, we observed central linear enhancement, surrounded by multiple enhancing punctate nodules 1-2 mm in diameter, clustered in a masslike structure with an arborized appearance. On T2-weighted images, the lesions were hyperintense with associated surrounding vasogenic edema and a mass effect. We have not observed this pattern of enhancement in association with other CNS worm infections or disease processes, nor have we found it described in the literature. Indeed, this appearance is so characteristic that when the 32-year-old man with seizures was initially presented at rounds as a patient with an unknown diagnosis, all the neuroradiologists familiar with the two other patients made a prospective, presumptive diagnosis of cerebral schistosomiasis on the basis of the contrast-enhanced T1-weighted MR imaging findings alone. Although our review of previous reports in the literature leads us to believe that the enhancement pattern we have observed may not be a sensitive indicator for CNS schistosomiasis, it is, in our experience, a specific one.
At biopsy, the enhancing nodules seen in our patients were thought to represent granuloma formation with extensive surrounding inflammation and possible venous congestion (Fig. 3D). Such granulomatous lesions are believed to represent either miliary pseudotubercles or confluent granulomata containing fibrosis, necrosis, hemorrhage, thrombosis, demyelination, calcification, and arteritis [5]. The morphology and placement of the spine (absent, lateral, or terminal) of the ova can be used to identify the schistosomal species: S. mansoni has a broad lateral spine, as seen in our two patients with cerebral involvement (Fig. 3E). S. haematobium has a prominent terminal spine, and S. japonicum has a rudimentary or absent spine. We postulate that the central linear enhancement that we observed is the result of slow blood flow and local venous obstruction caused by the anomalous migration of the adult worm into the leptomeningeal veins. Such placement might result in the concentration of ova at a focal region, forming a nodular mass.
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Praziquantel combined with corticosteroid therapy is the current treatment of choice for CNS schistosomiasis. Improvement in the patient's condition usually occurs within 6 weeks, with complete resolution within 6 months [12]. A favorable outcome depends on early diagnosis with immediate treatment. Ischemic changes in the spinal cord may lead to fibrosis and poor response to medical management. All of our patients were found to have had complete resolution of abnormal findings on follow-up imaging studies. The patient with spinal involvement and clinically diagnosed anterior spinal artery syndrome (considered a rare complication [5]), however, had residual lower extremity sensory and motor deficits.
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