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Neuroradiology

, 51:145 | Cite as

Ring-shaped lateral ventricular nodules: an incidental finding on brain magnetic resonance imaging

  • Taro Shimono
  • Makoto Hosono
  • Ryuichiro Ashikaga
  • Seishi Kumano
  • Izumi Imaoka
  • Yukinobu Yagyu
  • Masahiro Okada
  • Masatomo Kuwabara
  • Takamichi Murakami
Diagnostic Neuroradiology

Abstract

Introduction

We have occasionally seen ring-shaped lateral ventricular nodules <1 cm in diameter during routine brain magnetic resonance imaging (MRI). We investigated retrospectively clinical and MRI findings of the nodules.

Materials and methods

Review of radiological records was performed for 39,607 patients who underwent brain MRI between January 2001 and April 2008. Nodules were assessed for number, location, shape, and signal intensity, which was determined based on the range of signal intensity from gray to white matter on T1- and T2-weighted imaging. Fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted imaging (DWI), contrast enhancement characteristics, and serial MRI changes of nodules were assessed when available.

Results

Nine of 39,607 patients (0.023%) showed the nodules. No symptoms associated with the nodules. Among the nine patients, 11 nodules were identified (one nodule in seven patients (77.8%) and two nodules in two patients (22.2%)). Location was limited to the roof of the body for six nodules (54.5%) and the frontal horn for five patients (45.5%). All nodules (100%) were round and isointense on T1- and T2-weighted imaging. On FLAIR imaging of eight nodules, six (75%) were hyperintense, and two (25%) were isointense. On DWI of seven nodules, all nodules (100%) were isointense. None of seven nodules (0%) examined using postcontrast MRI showed enhancement. None of eight nodules (0%) examined using serial MRI (range, 4–60 months) showed changes in morphology over time.

Conclusion

These nodules were incidentally encountered and shared similar MRI features. Although pathological confirmation was lacking in our cases, these nodules may be of nonaggressive nature.

Keywords

Lateral ventricle Neoplasm Magnetic resonance imaging 

Introduction

Unexpected abnormalities are occasionally discovered during routine brain magnetic resonance imaging (MRI) examinations, usually in the setting of an investigation for some other reason [1].

Under such circumstances, we have occasionally seen ring-shaped lateral ventricular nodules <1 cm in diameter on axial images during routine MRI. Abnormalities that affect the lateral ventricles can be of diverse etiology, including some uncommon tumors. A wide variety of radiological features can be seen that may be nonspecific in some cases, making differentiation of the pathology involved difficult or even impossible. The location deep within the brain makes it difficult to reach these lesions surgically, and a pathological diagnosis is not always easy to achieve [2, 3, 4]. Some small lesions of the lateral ventricles, when asymptomatic or transiently symptomatic, do not require pathological diagnosis and are followed up without surgery.

Although radiological findings for diverse lesions of the lateral ventricles have been well investigated, no articles appear to have discussed MRI findings of small ring-shaped lateral ventricular nodules as we have encountered. The purpose of this study was thus to retrospectively evaluate clinical and MRI findings of these ring-shaped lateral ventricular nodules <1 cm in diameter on axial images.

Materials and methods

Patients

We retrospectively reviewed an electronic database of radiology reports of 39,607 patients who underwent brain MRI examinations at our institution between January 2001 and April 2008 and searched retrospectively for reports that indicated ring-shaped lateral ventricular nodules <1 cm in diameter on axial images. The reasons for the original referral for brain MRI examinations were diverse. The patients with the nodules were identified with an electronic word search of the full radiology reports by using the four keywords “ring-shaped,” “lateral ventricular/ventricle,” “nodule/mass,” and “<1 cm” including variations in spelling, synonym, and hyphenation. After the searching for the reports, clinical and MRI findings of the identified patients of the lateral ventricular nodules were retrospectively evaluated.

This retrospective study was approved by the institutional review board, and the informed consent requirement was waived. Patient anonymity was maintained.

MRI technique

All patients underwent MRI using 1.5-T systems with varying imaging techniques, including the use of different types of MRI scanner. Axial noncontrast T1- and T2-weighted imagings were obtained in each case, along with other sequence images relevant to each case.

Spin-echo pulse sequences were employed in every case, with the use of settings for routine brain imaging on each scanner at original referral for brain MRI examinations. Noncontrast T1-weighted conventional spin-echo images were obtained using a repetition time (TR) of 450–509 ms and an echo time (TE) of 10–15 ms. T2-weighted fast spin-echo images were obtained with TR of 3,840–4,200 ms and TE of 100–120 ms. In each sequence, two signals were acquired, with an image acquisition matrix of 256 × 256 or 400 × 512, field-of-view (FOV) 22 or 23 cm, and section thickness of 6 mm with a 1.2-mm intersection gap, depending on the imaging system used. Axial and coronal postcontrast T1-weighted images were obtained using the same parameters as noncontrast T1-weighted imaging when available.

Additional imaging sequences, when available, included axial single-shot spin-echo echo-planar diffusion-weighted imaging (DWI; TR, 3,386 ms; TE, 84 ms; b factor = 1,000 s/mm2; matrix, 112 × 256 matrix; section thickness, 6 mm with a 1.2-mm intersection gap; FOV, 23 cm; two signals acquired; isotropic images evaluated) and coronal fast fluid-attenuated inversion recovery (FLAIR) imaging (TR, 8,000 ms; TE, 100 ms; inversion time, 2,200 ms; matrix, 256 × 512; section thickness, 6 mm with a 1.2-mm intersection gap; FOV, 23 cm; one signal acquired).

MRI evaluation

MRI of the lateral ventricular nodules of all the identified patients was evaluated visually by two experienced neuroradiologists (>15 years experience each) blinded to clinical data, and final decisions on findings were reached by consensus. Observers assessed number, location (right or left and anatomical region), and shape (round or lobulated) of the ring-shaped lateral ventricular nodules in all the identified patients.

In addition, observers assessed signal intensity of the ring portion of the nodules, which was determined based on the range of signal intensity from deep gray matter to adjacent white matter observed on T1- and T2-weighted imaging in all the identified patients and additionally on FLAIR images and on DWI when available. The range of signal intensity from deep gray matter to adjacent white matter was used as a reference because the small size of the nodules and consequent partial volume effect might impede precise evaluation of the signal intensity of the nodules. Signal intensity of the core portion of nodules relative to that of cerebrospinal fluid (CSF) was also assessed on noncontrast T1- and T2-weighted imaging in all the identified patients.

When postcontrast studies were performed, contrast enhancement characteristics of lateral ventricular nodules were assessed. When follow-up MRI studies were performed, observers also assessed the presence or absence and characteristics of serial MRI changes to the lateral ventricular nodules.

Results

Nine of 39,607 patients (0.023%; six men, three women) were identified with ring-shaped lateral ventricular nodules <1 cm in diameter on axial MRI. Mean age of the nine patients was 49.8 years (range, 28–77 years). The reasons for the original referral for brain MRI examinations of the nine patients were screening for headache in three patients, screening for brain metastasis in two (one was asymptomatic and one was headache), screening for transient facial weakness in one, preoperative evaluation of meningioma in one, preoperative evaluation of pituitary adenoma in one, and screening after percutaneous transluminal coronary angioplasty in one, respectively. No records of long overseas (from our country) stays were identified in any of these patients.

Five of the nine patients (55.6%) presented with neurological symptoms (headache, n = 4; weakness, n = 1) at first, but symptoms resolved spontaneously and were judged as unassociated to the lateral ventricular nodules.

All the nine patients underwent axial noncontrast T1- and T2-weighted imaging. Among the nine patients, six patients underwent FLAIR, five underwent DWI, and six underwent axial and coronal postcontrast T1-weighted imaging, respectively. Among the nine patients, three had undergone MRI once, and the other six patients had undergone serial MRI with a mean follow-up of 32.7 months (range, 4–60 months). Among the nine patients, abnormal MRI findings except the lateral ventricular nodules were negative in six patients, hydrocephalus in one, a meningioma in one, and a pituitary adenoma in one, respectively.

No histopathological examinations of surgical or biopsy specimens of lateral ventricular nodules were performed due to clinical decisions by each primary physician relevant to each case.

All the nine patient data, including clinical and MRI findings, are summarized in Table 1.
Table 1

Clinical and MRI findings for nine patients with ring-shaped lateral ventricular nodules <1 cm in diameter.

Patient

Age (years)/sex

Symptoms

Location

Shape

Signal intensity on T1WI

Signal intensity on T2WI

Signal intensity on FLAIR

Signal intensity on DWI

Contrast enhancement

Outcome/follow-up period (months)

1

28/M

Headache

Roof of left body

Round

Isointense

Isointense

Hyperintense

Isointense

No

No change/4

2

38/M

Headache

Roof of left body

Round

Isointense

Isointense

N/A

N/A

No

No change/60

3

38/M

None

Roof of left body

Round

Isointense

Isointense

N/A

N/A

No

No change/5

4

41/M

None

Lateral tip of left frontal horn

Round

Isointense

Isointense

Hyperintense

Isointense

No

No change/60

Roof of left frontal horn

Round

Isointense

Isointense

Isointense

Isointense

No

No change/60

5

46/F

Headache

Roof of right body

Round

Isointense

Isointense

N/A

N/A

No

N/A

6

53/M

None

Roof of left body

Round

Isointense

Isointense

Isointense

Isointense

N/A

N/A

7

54/F

Weakness

Roof of left frontal horn

Round

Isointense

Isointense

Hyperintense

Isointense

No

No change/55

8

73/F

Headache

Roof of right frontal horn

Round

Isointense

Isointense

Hyperintense

Isointense

N/A

No change/12

Roof of left frontal horn

Round

Isointense

Isointense

Hyperintense

Isointense

N/A

No change/12

9

77/M

None

Roof of left body

Round

Isointense

Isointense

Hyperintense

N/A

N/A

N/A

Patients 4 and 8 each displayed two lateral ventricular nodules

Signal intensity, signal intensity of the ring portion of the lateral ventricular nodules was determined based on the range of signal intensity from gray to white matter, NA not applicable, T1WI T1-weighted imaging, T2WI T2-weighted imaging, FLAIR fluid-attenuated inversion recovery, DWI diffusion-weighted imaging

While seven patients (77.8%) showed a single lateral ventricular nodule (Fig. 1), two patients (22.2%) showed two nodules, with one nodule in each of the bilateral lateral ventricles and the other showing both nodules in the left lateral ventricle (Fig. 2). A total of 11 lateral ventricular nodules was thus identified among the nine patients.
Fig. 1

Screening results for an asymptomatic 77-year-old man (patient 9) after percutaneous transluminal coronary angioplasty. a Axial T1-weighted imaging (TR, 450 ms; TE, 15 ms) and b axial T2-weighted imaging (TR, 3,840 ms; TE, 120 ms) obtained at the level of the roof of the lateral ventricles show a ring-shaped left lateral ventricular nodule (arrow). Signal intensity of the ring portion of the lateral ventricular nodule is isointense to the signal intensity range from gray to white matter, and the core portion of the nodule is isointense relative to CSF on both T1- and T2-weighted imaging. c Coronal FLAIR imaging (TR, 8,000 ms; TE, 100 ms; inversion time, 2,200 ms), obtained at the level of the body of the lateral ventricle, shows a ring-shaped nodule (arrow) attached to the roof ependyma and protruding into the left lateral ventricle. Signal intensity of the ring portion of the lateral ventricular nodule is hyperintense relative to the signal intensity range from gray to white matter, and the core portion of the nodule is isointense relative to CSF on FLAIR imaging

Fig. 2

An asymptomatic 41-year-old man (patient 4) in preoperative screening for meningioma (not shown). a, b Axial noncontrast T1-weighted imaging (TR, 509 ms; TE, 10 ms) at the level of the lateral ventricles show two ring-shaped left lateral ventricular nodules at the lateral tip (a: arrow) and medial roof (b: arrow) of the left frontal horn. Signal intensity of the ring portion in both nodules is isointense relative to the signal intensity range from gray to white matter. c, d Axial postcontrast T1-weighted imaging (TR, 509 ms; TE, 10 ms) at the same levels as a and b show the nodules (arrow) with no contrast enhancement

On MRI among the 11 lateral ventricular nodules of the nine patients, nine nodules (81.8%) in eight patients were on the left and the remaining two nodules (18.2%) of two patients were on the right. Nodules were located on the roof of the body in six nodules (54.5%) of six patients and in the frontal horn in five nodules (45.5%) of three patients, with no other locations in the lateral ventricle identified.

Shape of all 11 ring-shaped lateral ventricular nodules (100%) was round and had thick ring portion on axial images. The nodules attached on ependyma and protruded into lateral ventricles.

Signal intensity of ring portion of all 11 ring-shaped lateral ventricular nodules (100%) was isointense relative to the signal intensity range from deep gray matter to adjacent white matter observed on noncontrast T1- and T2-weighted imaging. Signal intensity of the core portion in all 11 nodules (100%) was isointense relative to CSF on noncontrast T1- and T2-weighted imaging. On FLAIR imaging of eight nodules in six patients, signal intensity of the ring portion of the lateral ventricular nodules was hyperintense relative to the signal intensity range from deep gray matter to adjacent white matter in six nodules (75%) of five patients and isointense in two nodules (25%) of two patients. On DWI of seven nodules in five patients, signal intensity of the ring portion of lateral ventricular nodules was isointense relative to the signal intensity range from deep gray matter to adjacent white matter in all nodules (100%).

None of the seven nodules (0%) of six patients who underwent postcontrast T1-weighted imaging showed enhancement. None of the eight nodules (0%) followed in six patients showed morphological changes over the interval.

Discussion

Ring-shaped lateral ventricular nodules in this study seemed asymptomatic, and the majority, eight of the all 11nodules (72.7%), displayed no rapid growth but shared similar MRI features and anatomical location. On FLAIR imaging, the ring portion of the majority, six of eight nodules (75%), was hyperintense relative to the signal intensity range from gray matter to white matter, and histology of these nodules seemed to differ from normal brain parenchyma.

In our radiological database, the sex and age distribution of all patient population who underwent brain MRI examinations cannot be displayed. So, it is difficult to determine whether there is sex- and age-related predominance among the nine patients with the nodules.

In the differential diagnosis of small lateral ventricular nodules, the most common pathological entities are subependymal heterotopias and subependymal nodules. Subependymal heterotopia is defined as heterotopic gray matter situated adjacent to the wall of the lateral ventricles. Clinically, patients with this pathology present with seizures. Heterotopic tissue appear either as broad bands lying along the superolateral border of the lateral ventricle or multiple nodules protruding into the lateral ventricle. These lesions always appear isointense to normal gray matter on all sequences, and contrast enhancement is absent [5]. Subependymal nodules are found in 90–100% of patients with tuberous sclerosis. The classic diagnostic criteria for tuberous sclerosis comprise facial lesions, seizures, and mental retardation. Subependymal nodules tend to display multiple occurrences, and the majority is located near the caudate nucleus adjacent to the foramen of Monro. Subependymal nodules show variable signal characteristics and often calcify, and the majority demonstrate some enhancement [3, 6, 7]. However, subependymal heterotopias and subependymal nodules never show a ring-shaped appearance and obviously differ from the nodules in this study.

Not uncommon mass lesions affecting lateral ventricles are astrocytoma, subependymal giant cell astrocytoma, meningioma, choroid plexus papilloma/carcinoma, central neurocytoma, ependymoma, subependymoma, metastases, lymphoma, cavernous hemangioma, and cysticercosis [2, 3, 4, 8, 9, 10, 11]. Among these, subependymoma has the most similar nature to the nodules in this study. Subependymoma shows a heterogeneous MRI appearance that reflects the presence of small intratumoral cysts, calcifications, and hemorrhage. Subependymoma is the most frequent nonenhancing neoplasm found in the lateral ventricle and should be considered when a well-defined nonenhancing tumor is found in the lateral ventricle of middle-aged and elderly adults, mostly if found incidentally [2, 3, 4, 10, 11]. However, to the best of our knowledge, subependymoma has not been described with a ring-shaped appearance.

Rare numerous mass lesions affecting the lateral ventricles have been reported in the literature, including ganglioglioma, oligodendroglioma, pilocytic astrocytoma, glioblastoma, primitive neuroectodermal tumor, sarcoma, teratoma, schwannoma/perineuroma/malignant schwannoma, fibroma, solitary fibrous tumor, dysembryoplastic neuroepithelial tumor, and hamartoma [2, 3, 4, 12, 13, 14, 15]. However, these lesions do not demonstrate a ring-shaped appearance and are much less frequent than the nodules identified in this study (0.023%).

Some normal variations and artifacts may show a nodular appearance and cause erroneous diagnosis of mass lesion, such as asymmetry of the lateral ventricle, coarctation of the frontal horn, subependymal cyst/pseudocyst, intraventricular prominence of the occipital horn, and lateral ventricular CSF flow-related artifacts [16, 17, 18, 19]. Among these, coarctation of the frontal horn has the most nodular appearance. Coarctation of the frontal horn refers to a condition of unknown etiology in which the ependyma of the frontal horns are fused, found in about 6% of the normal population [17]. Coronal imaging reveals adhesion between the two facing ventricular walls. Coarctation of the frontal horn may perhaps show a ring-shaped appearance if redetachment had occurred, although no such cases have been reported in the literature.

To the best of our knowledge, only two articles have reported nodules of the lateral ventricles resembling those encountered in our study [20, 21]. Shigematsu et al. [20] showed such nodules without pathological confirmation by intracranial virtual MRI endoscopy using a constructive interference in steady-state sequence. These nodules were simply labeled “lateral ventricle nodules,” and no detailed discussion was provided of nodule characteristics. Though intracranial virtual MRI endoscopy revealed such nodules, the nodules have not been reported during practical endoscopic neurosurgery. Another very similar nodule was reported as a neuroglial/glioependymal cyst [21]. Neuroglial/glioependymal cysts are rare lesions which occur in a wide variety of sites throughout the neuroaxis and lined by a single epithelial layer [21, 22, 23]. Though there is a high possibility that neuroglial/glioependymal cysts are regarded as the nature of the ring-shaped nodules, most reported images of neuroglial/glioependymal cysts are different from current images of the ring-shaped nodules [22, 23].

In the absence of pathological confirmation, possibilities regarding the nature of these ring-shaped nodules include: (1) neuroglial cyst/glioependymal cyst; (2) inflammatory or reactive nodular formation of ependyma we have not discussed above, such as granuloma; (3) astrocytic gliosis reaction near subependymal veins [24]; (4) redetachment of the fused portion of coarctation of the frontal horn; and (5) a variant of subependymoma.

Some limitations have been identified in this study, including the retrospective nature of the study and the small sample size. This latter limitation is a function of the low incidence of the nodules. Radiological record review revealing nine of 39,607 patients (0.023%) whose brain MRI reportedly showed the ring-shaped nodules may give false negatives, as not all readers over the 7-year time span may have reported or recognized the finding, especially if the readers were not looking specifically for this finding. Thus, the actual incidence of the nodules may be higher than 0.023%. Although no progression of the eight nodules was observed in the six patients that underwent serial follow-up MRI, there still remains uncertainly about possible progression in the remaining three nodules in three patients. Furthermore, given the relatively large MRI slice thickness employed (section thickness of 6 mm with a 1.2-mm intersection gap) and the fact that not volume but diameter measurement of the nodules was performed, it is possible that very small increases were missed. Further investigation, particularly pathological clarification, is needed to elucidate the nature of these nodules. However, in this study, the nodules displayed benign behavior and required no treatment. We consider these nodules as “do-not-touch lesions” and recommend follow-up rather than immediate surgical treatment if such nodules are incidentally encountered with the characteristic ring shape on MRI.

In conclusion, we have incidentally encountered ring-shaped lateral ventricular nodules <1 cm in diameter in 0.023% of patients during routine brain MRI. The majority of the lesions showed no rapid growth and shared similar MRI features and anatomical location, occurring in the roof of body or frontal horn of the lateral ventricles. Although pathological confirmation was lacking, these nodules may be of nonaggressive nature.

Notes

Conflict of interest statement

We declare that we have no conflict of interest.

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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Taro Shimono
    • 1
  • Makoto Hosono
    • 1
  • Ryuichiro Ashikaga
    • 1
  • Seishi Kumano
    • 1
  • Izumi Imaoka
    • 1
  • Yukinobu Yagyu
    • 1
  • Masahiro Okada
    • 1
  • Masatomo Kuwabara
    • 1
  • Takamichi Murakami
    • 1
  1. 1.Department of RadiologyKinki University School of MedicineOsaka-SayamaJapan

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