Incidental optochiasmatic cavernoma: Case report of an unusual finding on 3 Tesla MRI

Abstract

Cavernoma is a vascular hamartoma, which represents 10–20% of all central nervous system vascular malformations. The majority (80%) of them are supratentorial, while involvement of the cranial nerves and the optic pathways is extremely rare. The main clinical presentation of optochiasmatic cavernomas consists of chiasmatic apoplexy, which is a neurosurgical emergency. Here, we report a case in which the finding was incidentally detected in a 49-year-old man. We describe the imaging characteristics of the lesion in such a rare location, highlighting the role of magnetic resonance imaging (MRI) (specifically 3 Tesla) in the management of asymptomatic patients.

Introduction

The incidental detection of an optochiasmatic cavernoma (OCM) can raise problems for differential diagnosis and treatment, since there is a lack of data in the literature about asymptomatic patients. Generally, the malformation presents with visual impairment although some other clinical pictures are described, including subarachnoid haemorrhage. Here, we describe the main characteristics of this very unusual lesion found in an asymptomatic patient. We also underline relevant imaging features to reach a diagnosis, highlighting the role of magnetic resonance imaging (MRI) examinations performed with 3 Tesla equipment. We also suggest some clues for differential diagnosis.

Case report

A 49-year-old man was referred to our institution for a second opinion after being studied at another hospital for dizziness. His history was negative for relevant pathologies, tinnitus, hearing loss and visual disturbances. Neurological and campimetric examinations were normal. A computed tomography (CT) examination had shown a hyper-dense rounded nodule at the suprasellar region. The finding was evocative of various pathologies (e.g. suprasellar aneurysm), but a subsequent MRI scan was not conclusive, since it suggested a possible craniopharyngioma. At our institute, the high contrast and anatomical resolution obtained with a 3 Tesla scanner allowed us to confirm the presence of a 1 cm lobulated lesion at the optochiasmatic junction with extension towards the left optic tract. The nodule presented with smooth, thin and hypo-intense borders, with an inhomogeneously hyper-intense core on the T2W images (Figures 1 and 2), and it did not enhance on T1W post-gadolinium images (Figures 3 and 4). The pituitary gland was normal, whereas the pituitary stalk appeared slightly displaced (Figures 1 and 3). In addition, on the T2* gradient recalled echo (GRE) images, an hypo-intense ‘blooming’ spot compatible with a ‘black dot-like’ vascular malformation was also found at the right post-Rolandic region (Figure 5). No alterations of the seventh/eighth cranial nerves and of the inner ear were found on either side. After the MRI, the hypothesis of an OCM was confirmed. Six months after diagnosis, the patient remains asymptomatic with normal campimetry, and a follow-up MRI did not show substantial changes to the chiasmatic lesion (Figure 3), whereas the black dot-like supratentorial alteration appeared slightly increased (Figure 5).

Figure 1.

T2 weighted turbo spin echo images (on three planes) show an inhomogeneously hyper-intense nodule 1 cm in size (arrow, a) with the so-called ‘popcorn’ appearance. The lesion is suprasellar, with slight displacement of the pituitary stalk (arrowhead, b).

Figure 2.

The T2 GRE images define the hemosiderin component of the lesion (arrow, ‘blooming effect’), making this sequence the ‘gold standard’ for detecting the malformation.

Figure 3.

T1 turbo spin echo images before (a) and after gadolinium injection (b, first MRI; c, follow-up MRI): the chiasmatic lesion (arrowheads) shows no enhancement and no enlargement at the follow-up MRI performed six months later. The hypophysis appears normal (dotted arrow, b–c).

Figure 4.

Axial (a) and coronal (b) T1 turbo spin echo post-contrastographic images. The chiasmatic involvement is evident (arrowheads on a: left optic nerve and optic tract; arrow on b: the chiasm).

Figure 5.

The T2 GRE images demonstrate a right post-Rolandic ‘black dot-like’ lesion consistent with a small vascular malformation. On follow-up, the alteration (empty arrow, b) appears slightly enlarged compared with the previous MRI realised by the same 3 Tesla scanner (arrowhead, a).

Discussion

We use the terms ‘cavernoma’ and ‘cavernous malformation’ (CM) to designate a vascular hamartoma^1–3 with a prevalence of 0.4–0.9%⁴ within the general population. The malformation grows as a result of recurrent internal haemorrhages,⁵ unlike [hem]angiomas (the term also frequently reported in the literature) which are ‘true’ benign vascular neoplasms.^2,6–8 CMs represent 10–20% of all central nervous system (CNS) vascular malformations,^4,9 being located everywhere inside the CNS³ (80% supratentorial,⁴ especially subcortical in the frontal, temporal lobes);^5,10–12 both sporadic (75%) and multiple/familial forms (10–30%) are recognised.^2,13 CMs rarely involve the cranial nerves^3–5,14 or the optic pathways (≤1%),¹ and are typically 5–30 mm in size, consisting of aberrant, immature, thrombosed, low-flow vessels surrounded by a gliotic plan anchored to the adjacent nervous tissue^11,14 (without neural tissue inside the nodule,^1,3,10,11 unlike arteriovenous malformations⁵). The annual rate of bleeding increases from 0.25% to 20%,⁴ with a re-bleeding rate of 3.8–22.9%.¹ Mass effect, oedema, irritation and ischemia induced on the surrounding tissue by intrinsic/extrinsic haemorrhages cause the clinical onset.⁴ Even if there is a lack of clear evidence,^11,15 it is believed that the bleeding of OCMs induces symptoms more frequently than cavernomas located elsewhere.^4,15,16 For this reason, symptomatic OCMs are considered a neurosurgical emergency.^4,12,13 While seizures are the most common presentation of intracerebral cavernomas,^11,12 the symptoms of OCMs (second to fourth decades^1,12) are represented by a spectrum, with the most common picture consisting of chiasmatic apoplexy¹⁷ (acute chiasmal compression syndrome¹¹: sudden frontal/retro-orbital headache, acute mono-/bilateral hypovisus, hemianopia). Subacute visual deterioration has been reported,^1,3 especially in the weeks before acute onset. Subarachnoid haemorrhage^{1,3,5,10,11,13–15} and hypothalamic-hypophyseal disorders have also been reported (e.g. growth hormone/adrenocorticotropic hormone deficits, polyuria, polydipsia^11,18). Symptoms are precipitated by alcohol consumption, pregnancy or physical effort.^5,14

In our case, none of the above-described symptoms were found, since dizziness was not correlated with the chiasmatic lesion. Therefore, imaging acquired a pivotal role to detect and characterise the lesion to confirm its intrachiasmatic location, allowing the differentiation from more aggressive processes. At angiography, these lesions remain occult in most cases^1,4,14 because of their low blood flow, internal thrombosis⁵ and absence of ectatic feeding vessels,^1,5 even if a slight contrast blush can occasionally be found during the capillary phase.^5,12 On CT scans, the OCMs appear as lobulated, well-marginated, slightly hyper-dense suprasellar nodules with poor/absent enhancement, associated with chiasmatic enlargement.^1,5,14 Microcalcifications can be found in 40–60%,^1,5,6,14 while fat components are absent. The CT morphologic features are also demonstrated by MRI, which is the most sensible and specific diagnostic tool.^1,4,12,14 Because of the difficult and narrow space in which the OCMs are located, the high spatial/contrast resolution guaranteed by MRI, especially by 3 Tesla scanners, is crucial for diagnosis.^4,15,16 The MRI signal behaviour of cavernomas has been classified by Zabramski.¹⁹ The typical ‘popcorn’ appearance on T2 weighted images consists of a thin, hypo-intense hemosiderin rim surrounding an inhomogeneous core of haemoglobin in various phases of degradation.^2,3,5,14 It is important to note that the hypo-intense rim can lack in OCMs because of the lavage of the cerebrospinal fluid all around the lesion.^1,14 A mono-/bilateral thickening of the chiasm represents another useful imaging clue.^1,14 The T2*GRE⁴ and the susceptibility weighted images (SWI), in particular on 3 Tesla scanners, are essential to characterise and to increase the conspicuity of the malformation because of the hypo-intense ‘blooming’ effect of hemosiderin.^6,16 Diffusion and perfusion weighted imaging are less useful for diagnosis (mask effect of hemosiderin). Extrinsic haemorrhages spreading inside the chiasm can mask the underlying lesion: in such cases, MRI follow-up can allow the correct diagnosis.⁵ At follow-up, OCMs can increase in volume (recurrent microbleedings), showing changes in their signal intensity.^4,14

Our patient was asymptomatic. Thus, he did not undergo surgery, and histological confirmation was therefore lacking. In any case, the location of the lesion and its distinctive ‘popcorn’ appearance were indicative of the final diagnosis. Moreover, the further post-Rolandic ‘black dot-like’ vascular malformation that was detected supported the hypothesis, since an association of more than one cavernoma has been described.^1,2,10,11,13 We had to exclude some other sellar/suprasellar lesions to reach the diagnosis. We ruled out an aneurysm (by magnetic resonance angiography, which showed a normal anatomy of the circle of Willis (Figure 6)), a craniopharyngioma (CRF) and a haemorrhagic pituitary adenoma, since these latter induce morphologic alterations of the pituitary gland and of the sella turcica. Furthermore, at MRI, both CRF and haemorrhagic adenoma can show a cystic appearance. In particular, CRFs present with hyper-intense cysts on T1 weighted images with enhancing solid components.¹ Other sellar/suprasellar lesions to consider in differential diagnosis are summarised in Table 1.^1,9,14,20

Figure 6.

MR-angiography image does not demonstrate abnormalities of the circle of Willis. In particular, no aneurysms of the anterior communicating artery were found.

Table 1.

Elements of differential diagnosis on MRI for some sellar/suprasellar lesions.

Suprasellar aneurysm	• Even if partially thrombosed, flow void signal can be found • Communication with circle of Willis detectable at MRA
Craniopharyngioma	• Proteinaceous fluid-filled cysts hyper-intense on T1 weighted images • Enhancement of solid components • Pituitary/sellar morphologic alterations • Calcifications, hypo-intense on MRI, frequently associated
Haemorrhagic pituitary adenomas	• Partially cystic appearance with fluid-fluid levels • Sellar morphologic alterations • Pituitary gland not well-delineated
Arteriovenous malformation	• Nidus of ectatic vessels (‘bag of worms’, flow voids and  contrast enhancement at MRI)
Optic/hypotalamic gliomas	• Haemorrhage/calcifications not typical • Only 10% in patients older than 20 years of age
Parasellar/optic sheath meningiomas	• Isointense with grey matter in all sequences • Strong enhancement • Optic nerve sheath involved, not optic chiasm • Sellar bone remodelling can be found • Dural tail
Germ-cell tumour, metastases (history of cancer, e.g. breast/lung cancer)	• Enhancement present
Dermoid/epidermoid	• Fat-like MRI appearance • Restriction on diffusion weighted imaging

MRI, magnetic resonance imaging; MRA, magnetic resonance angiography.

Surgical excision is mandatory for symptomatic OCMs^4,5: free margins of resection prevent re-haemorrhage,^1,5,10,14 providing a good prognosis (80–90% clinical stabilisation and improvement/recovery of the visual function).^1,3,11,13,16 Radiosurgery should be excluded to avoid re-bleeding and damage to the optic pathways.^1,11,15 For asymptomatic OCMs, even if preventive surgery is considered,^9,14,21 the best management could consist in follow-up²² (see comments in Deshmukh et al.¹³).

Conclusions

A discussion about the therapeutic work-up of incidental OCMs lacks evidence-based confirmation. As the reported case demonstrates, when surgery is not performed, the MRI is pivotal in the management of this condition, since in a ‘wait-and-see’ approach, this imaging modality represents the gold standard for follow-up.¹⁶ In asymptomatic patients, awareness of the correct diagnosis made by MRI could allow prompt surgery in case of future onset of symptoms, increasing the chances of visual recovery. The finding of more than one malformation could suggest an hereditary form of the condition. MRI screening of the patient’s family members could therefore be evaluated. Finally, we highlight that the conspicuity of OCMs is increased by using a 3 Tesla MRI scanner, which furthermore guarantees a higher anatomic/contrast resolution, which is useful to delineate the morphologic and signal intensity features of intrachiasmatic lesions better (Table 2).

Table 2.

Take home messages: role of MRI in asymptomatic patients.

• Gold standard in differential diagnosis/follow-up

• High grade of suspicion can allow prompt surgery and better prognosis when the lesion becomes symptomatic

• Guide for neurosurgical approach

• Detection of other vascular malformations throughout the central nervous system

• Screening in patient’s family members if more than one lesion found

• 3 Tesla scanners allow higher contrast/spatial resolution and increase the blooming effect and the lesion conspicuity

Funding

This work received no grant from any funding agency in the public, commercial or not-for-profit sectors.

Conflict of interest

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.