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LETTER TO EDITOR
Year : 2019  |  Volume : 9  |  Issue : 4  |  Page : 123-124

Symptomatic ventrolateral proatlas anomaly—A rare and under recognized cause of Chiari malformation with hindbrain herniation


Consultant Neurosurgeon, Department of Neurosurgery, Kokilaben Dhirubhai Ambani Hospital, Mumbai, Maharashtra, India

Date of Submission24-Apr-2020
Date of Acceptance10-May-2020
Date of Web Publication11-Nov-2020

Correspondence Address:
Dr. Hrishikesh Sarkar
Department of Neurosurgery, Kokilaben Dhirubhai Ambani Hospital, Mumbai, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ais.ais_22_20

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How to cite this article:
Sarkar H. Symptomatic ventrolateral proatlas anomaly—A rare and under recognized cause of Chiari malformation with hindbrain herniation. Arch Int Surg 2019;9:123-4

How to cite this URL:
Sarkar H. Symptomatic ventrolateral proatlas anomaly—A rare and under recognized cause of Chiari malformation with hindbrain herniation. Arch Int Surg [serial online] 2019 [cited 2020 Nov 27];9:123-4. Available from: https://www.archintsurg.org/text.asp?2019/9/4/123/300561



Sir,

Proatlas anomalies are associated with reduced posterior fossa volume with resultant tonsillar ectopia in 33% of the cases.[1],[2] Sparse literature exists to explain the existence and pathophysiology of such a disorder.[3] We report a rare case of symptomatic proatlas anomaly which was associated with hindbrain herniation and syrinx formation.

A 16-year-old girl presented with two episodes of blackouts while going to school and ataxia for the past 3 months. She was diagnosed as type-1 Chiari malformation elsewhere and referred to our center. Magnetic resonance imaging (MRI) and computed tomography (CT) of the craniovertebral junction (CVJ) showed left sided medialized occipital condyle compromising the foramen magnum [Figure 1]. She underwent neuronavigation-guided transoral transpharyngeal odontoidectomy, resection of medialized left occipital condyle [Figure 2]a. This was followed by foramen magnum decompression and occipito cervical stabilization with rods and iliac graft [Figure 2]b. Postoperative CT scan of CVJ showed adequate decompression of CVJ [Figure 2]b, [Figure 2]c, [Figure 2]d. There was improvement in patient's gait following surgery.
Figure 1: Preoperative magnetic resonance imaging (MRI) of the craniovertebral junction (CVJ) showed left-sided foramen magnum stenosis (a). There is tonsillar herniation up to the posterior arch of C1. (b-d) Computed tomography (CT) of CVJ with reconstruction images showed medialised left occipital condyle compromising the foramen magnum ventrally

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Figure 2: (a) Intraoperative image showing resected medialised left occipital condyle (OC). Postoperative CT scan of CVJ showed adequate decompression of CVJ and occipito cervical stabilization with rods and (b-d)

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Developmental anomalies around the foramen magnum due to proatlas segmentation defects are very rare and hence there is a difficulty in understanding the embryology and pathological anatomy.[1],[2] Improper diagnosis and management could lead to disastrous outcome. Our patient was also diagnosed to have type-1 Chiari malformation elsewhere and had been advised, what seemed obvious, foramen magnum decompression.

According to Menezes,[4] the abnormal left occipital condyle represents an abnormality from the ventral rostral neural arch of the proatlas. This has been proposed to occur due to either non-segmentation or hyperplasia of the proatlas. In their analysis, such ventral bony masses from the clivus or medial occipital condyle occurred in 66% (44 of 72 patients), lateral or anterolateral compressive masses in 37% (27 of 72 patients), and dorsal bony compression in 17% (12 of 72 patients). Hindbrain herniation was associated in 33%.[4],[5]

The choice of approach (anterior/posterior) should be on the basis of location of the anomalous part. Therefore, with the embryological anomaly in the background, it was imperative for us to approach the problem ventrally as the main compression was from front. The location of the anomaly can be well demonstrated in 3D CT scan of the craniovertebral junction. In our case, we resected odontoid process to increase the space around the foramen magnum but this is debatable. Navigation technology was greatly useful in performing the ventral procedure. The ventral approach was followed by posterior fusion and iliac bone graft placement. The outcome was good and there were no further episodes of transient loss of consciousness.

This unique and rare case demonstrates Proatlas anomalies to be recognized as one of the causes of foramen magnum stenosis. Non appreciation and simply doing foramen magnum decompression could lead to neurological deterioration. Resection of the abnormal bony mass followed by CVJ stabilization is the treatment of choice. Navigation is a useful adjunct during surgery. CT scan of CVJ with reconstructive images should be done in every case of foramen magnum stenosis.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Gladstone J, Erickson-Powell W. Manifestation of occipital vertebra and fusion of atlas with occipital bone. J Anat Physiol 1915;49:190-9.  Back to cited text no. 1
    
2.
Gladstone RJ, Wakeley CP. Variations of the occipito-atlantal joint in relation to the metameric structure of the craniovertebral region. J Anat 1925;59:195-216.  Back to cited text no. 2
    
3.
Menezes AH, Fenoy KA. Remnants of occipital vertebrae: Proatlas segmentation abnormalities. Neurosurgery 2009;64:945-53; discussion 954.  Back to cited text no. 3
    
4.
Menezes AH. Honored guest presentation: Craniocervical developmental anatomy and its implications. Clin Neurosurg 2005;52:53-64.  Back to cited text no. 4
    
5.
Kotil K, Kalayci M. Ventral cervicomedullary junction compression secondary to condyles occipitalis (median occipital condyle), A rare entity. J Spinal Disord Tech 2005;18:382-4.  Back to cited text no. 5
    


    Figures

  [Figure 1], [Figure 2]



 

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