British Journal of Radiology (2004) 77, 963-965
© 2004 British Institute of Radiology
doi: 10.1259/bjr/77185587
Intracranial laterally based supratentorial neurenteric cyst
G S Tan, MRCP, FRCR1,
T Hortobágyi, MD, PhD2,
S Al-Sarraj, MB ChB, MSc, FRCPath2 and
S E J Connor, MRCP, FRCR3
Departments of 1 Radiology, 2 Clinical Neuropathology and 3 Neuroradiology, Kings College Hospital, Denmark Hill, London, UK
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Abstract
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Neurenteric cysts are rare developmental cysts lined by endodermal derived epithelium. We present the case of a 68-year-old patient presenting with seizures who was found to have an extra-axial low density lesion with associated wall calcification on CT. Aspiration and biopsy of the cyst revealed a neurenteric cyst. Such lesions of the lateral supratentorial convexity are extremely rare and calcification has not been previously reported in these intracranial cysts.
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Introduction
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Neurenteric cysts are uncommon developmental cysts lined by endodermal derived epithelium, which are very rarely found intracranially. There is some controversy in the literature in the nomenclature of these lesions. In fact the term neurenteric, endodermal, enterogenous or even epithelial-lined and respiratory cyst are used interchangeably. However, in recent years the term neurenteric cyst has gained increasing support in the neuropathological terminology [1] and is the term used in this paper. Here we report a case of a neurenteric cyst centred on the lateral supratentorial convexity, a location only described on two previous occasions [2, 3]. The calcification noted in the wall of this lesion has not been previously been reported in association with such a lesion.
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Case report
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A 68-year-old woman presented following two tonic–clonic seizures affecting all four limbs and lasting for a few minutes. She had a past medical history of diet controlled diabetes, hypertension, a myocardial infarct and pneumonia. On examination, her right arm and leg were weak with power 4/5 (UK Medical Research Council classification) but there was no sensory deficit. A CT scan showed an ovoid well defined extra-axial low attenuation lesion over the left frontal convexity extending from the superior frontal region down to just above the level of the sylvian fissure measuring 5 cm x 6.5 cm in maximal transverse dimensions. There was mass effect with midline shift to the right and effacement of the sulci of the left cerebral hemisphere. It did not undergo contrast enhancement and several nodules of calcification were seen at the periphery of the lesion (Figure 1
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Figure 1. Enhanced CT scan demonstrates an extra-axial cystic lesion over the left frontal convexity with two small nodules of rim calcification. There is no contrast enhancement of the cyst.
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A left frontal mini-craniotomy was performed and the cyst was aspirated. Macroscopically, the specimen consisted of opaque, creamy, pale, brown fluid and cyst membrane. Light microscopy revealed fragments of cyst wall comprising a thin collagen band lined on one side by ciliated columnar and in places pseudostratified epithelium. The other surface was covered by a few arachnoid cells (Figure 2 – main picture and inset A). The cyst contents were composed of autolysed red cells and necrotic tissue. Immunohistochemistry showed the cells of the cyst lining reacted with antibodies directed against epithelial epitopes such as cytokeratin (CAM5.2) and epithelial membrane antigen (EMA) (Figure 2 inset B), confirming their epithelial origin. The glial fibrillary acidic protein (GFAP), leucocyte common antigen (LCA), and S-100 protein was negative. Occasional epithelial cells contained periodic acid-Schiff (PAS) positive material in their cytoplasm as revealed by digested PAS reaction. The appearances were consistent with an extracerebral neurenteric cyst.
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Figure 2. Histological appearances of the cyst wall. The internal lining of the cyst is columnar and pseudostratified epithelium (thick arrow) residing on a thin layer of collagen. The outer surface of the cyst wall is covered by arachnoidal cells (fine arrow). Higher magnification shows the ciliated, columnar epithelium (inset A, arrow shows cilia). There is a strong epithelial membrane antigen (EMA) immunoreactivity of the internal epithelial lining (inset B). Haematoxylin and eosin (H&E) stain (main picture and inset A), EMA immunohistochemistry (inset B). Original magnifications 50 x , 630 x (inset A), 200 x (inset B).
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The patient made an uneventful recovery from surgery and was neurologically intact on discharge.
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Discussion
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Neurenteric cysts represent 0.7% of all spinal tumours and 16% of spinal cysts [3] where they usually occur as extramedullary intradural lesions. Intracranial locations are rare and usually located in the posterior fossa either anterior to the brainstem [4, 5], within the fourth ventricle [6] or in the cerebellopontine angle [7]. Other locations include the superior orbital fissure [4], optic nerve [4], parasellar and suprasellar area [8], septum pellucidum [9], oculomotor nerve [10] and third ventricle [11]. A supratentorial laterally based location has been previously confirmed and described on only two previous occasions [2, 3].
Neurenteric cysts are thin walled sacs containing usually clear and occasionally thick, colourless fluid [12]. Histologically, neurenteric cysts can be divided into three separate groups based upon the structure of their wall [1]. Type A cysts are covered by a single or pseudostratified layer of cuboidal or columnar epithelium. These may be ciliated or non-ciliated resembling respiratory or gastrointestinal epithelium, respectively. Certain other intracranial endodermal cysts may also contain a ciliated epithelium including colloid cyst of the third ventricle and Rathke's cleft cyst of the pituitary fossa. In type B cysts, the wall contains in addition, connective tissue components, glands, smooth muscle, lymphoid tissue and in exceptional cases even nerve ganglion. The type C cyst may in addition have glial elements such as ependymal cells, in the wall. The type B and C cysts may be confused with mature teratoma [13]. Approximately half of the cysts are lined by gastrointestinal type epithelium, 17% by ciliated columnar (respiratory) epithelium and the rest are of mixed type [14]. Foci of non-keratinizing squamous metaplasia may be encountered [15]. The presented case shows a Type A cyst with respiratory epithelium.
A neurenteric cyst is thought to occur when endoderm becomes displaced from its normal location (nasopharyngeal, respiratory tract or intestinal tract) to an ectopic position in the embryo. An explanation of the origin of neurenteric cysts is aided by a brief review of the relevant embryology. During embryogenesis mesoderm lying along the midline of the embryo forms the notochordal process [16]. The notochordal process contains a central lumen – the notochordal canal – which is continuous with the amniotic cavity through the primitive pit. The cells of the process subsequently intercalates with the subjacent endoderm and disappear at the midline which places the notochordal canal in continuity with both amniotic and yolk sacs. The communication is referred to as the neurenteric canal and exists for approximately 48 h after which the process separates from the endoderm and forms the definitive notochord [4, 5]. The cranial end of the notochord eventually forms the posterior clinoid portion of the clivus [5]. A neurenteric cyst is thought to result from fusion of the ectoderm and endoderm prior to notochord formation, persistence of endodermal cells attached to the notochord during excalation or partial regression of a duplicated neurenteric canal [4]. A neurenteric cyst could therefore theoretically arise at any level of the neuraxis that overlies the notochord – that is from the diencephalic–mesencephalic junction to the conus medullaris. It is postulated that some supratentorial neurenteric cysts originate from Seesel's pouch, which is an endodermal diverticulum appearing just behind the oropharyngeal membrane and in front of the rostral end of the cord [17]. However these theories would not account for a lateral supratentorial convexity location.
Neurenteric cysts are most frequently hypodense but occasionally hyperdense or isodense to brain on CT [8]. There may be rim enhancement [4]. MRI shows that the cyst contents are usually low signal on T1 and high signal on T2 weighted images although the signal may be altered if there is increased cyst protein content or haemorrhage [18]. Our case demonstrated wall calcification which has not previously been described in the setting of intracranial neurenteric cysts.
The imaging characteristics and location of the cyst may aid in formulating the correct diagnosis although other entities which should be considered in the differential diagnosis of an extra-axial supratentorial cyst are an arachnoid cyst, epidermoid, tumoural cyst, parasitic or larval cyst. Arachnoid cysts are developmental or acquired cysts and 5% are found over the frontal convexities [19]. Typically they demonstrate cerebrospinal fluid (CSF) signal on all MRI pulse sequences and CSF density on CT and do not demonstrate calcification. Epidermoid cysts are usually lobulated due to their soft pliable nature. They may demonstrate calcification in 10–25% of cases [19] however are rarely detected at the cerebral convexity. A tumoural cyst would be expected to enhance and demonstrate associated enhancing soft tissue. In racemose neurocystercicosis there are large cysts which return an attenuation or signal intensity similar to CSF on CT or MRI however they are more commonly multiple, located in the subarachnoid basal cisterns and sylvian fissure, they do not usually calcify and tend to result in associated enhancement of the leptomeninges [20, 21]. The combined imaging features and location of our case was exceptional for a neurenteric cyst but neither was it typical of other non-neoplastic, neoplastic or infectious cystic lesions and histological confirmation was ultimately required.
Received for publication August 11, 2003.
Revision received February 17, 2004.
Accepted for publication April 20, 2004.
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[Abstract]
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Abstract
Introduction
