Myelomeningocoele and a dermoid sinus-like lesion in a French bulldog

Abstract

A 2-year-old male French bulldog was presented for investigation of lumbosacral pain and hindlimb ataxia associated with urinary and fecal incontinence. Survey radiography, myelography, and computed tomography images were suggestive of a dermoid sinus with associated spina bifida. Surgical intervention led to a resolution of pain and neurological deficits. Histopathological analysis of the excised tissue was compatible with a myelomeningocoele of the 7th lumbar vertebra.

Abnormalities of the spinal cord and vertebral column (spinal dysraphism) are rare in dogs. In humans, a classification system distinguishes 3 types of spina bifida: open, closed (with externally visible abnormalities), and occult (with no externally visible abnormalities). Spina bifida is characterized by defective fusion of the embryonic neural tube resulting in incomplete development of the vertebral arch and often the overlying tissues. An accompanying protrusion of the meninges is termed a meningocoele, whilst a protrusion of both the meninges and the spinal cord itself is termed a myelomeningocoele. There are few reports of spina bifida associated with myelomeningocoele in the dog (1–4).

Dermoid sinus is a congenital malformation which occurs due to an incomplete separation between the neural tube and the ectodermal layer. Primarily seen in the Rhodesian ridgeback (5–11), this abnormality is also described in the vertebral column in other breeds including the shih tzu and the boxer (12), Boerboel (13), chow chow (14), golden retriever (15), Siberian husky (16), English springer spaniel (17), Yorkshire terrier (18), Pyrenean mountain dog (19), Chinese crested dog, Swedish vallhunds and a Burmese cat (20), Victorian bulldog (21), and English cocker spaniel (22).

This report describes a myelomeningocoele in a French bulldog, associated with a dermoid sinus-like lesion, and its surgical treatment.

Case description

A 2-year-old French bulldog was presented for evaluation of hindquarter pain and a sudden onset of reluctance to ambulate. The owners had also noted episodes of urinary and fecal incontinence over several months.

On clinical examination, the dog was in good body condition and the vital parameters were within normal limits. The dog displayed a guarded response to lumbosacral palpation. A skin depression was noted immediately cranial to the spinous process of the first sacral vertebra (S1) (Figure 1). On neurological examination, a bilateral hindlimb ataxia was evident. Proprioceptive deficits (absent correction of proprioceptive positioning) and reduced withdrawal reflexes were identified in both hindlimbs whilst the patellar reflexes were normal. The perineal reflex was diminished. No neurological abnormalities were found in the forelimbs. It was concluded that a lower motor neuron (LMN) lesion of the sciatic nerves was present, localized between the sixth lumbar vertebra (L6) and the third sacral vertebra (S3), consistent with cauda equina syndrome. The main differential diagnosis was a congenital compressive lesion of the lumbosacral region, although inflammatory, vascular, and neoplastic causes could not be ruled out.

Figure 1.

Lumbosacral skin depression.

Radiographs of the vertebral column permitted identification of several thoracic vertebral anomalies, often seen in this breed, such as wedge-shaped vertebrae (T6 and T8) without any significant deviation of the vertebral axis, as well as the absence of a spinous process at L7 vertebra.

Myelographic examination demonstrated, on lateral projection, a dorsal displacement of the ventral and dorsal contrast columns and the dural cone exiting the vertebral column between L7 and S1 (Figure 2). The vertebral canal caudal to S1 appeared to be void of contrast agent. The course of the dural cone appeared to correlate with the skin depression previously noted.

Figure 2.

Lateral view of a lumbosacral myelogram. Note the dorsal column deviation and the absence of the spinous process of L7.

These findings were strongly suggestive of a type II dermoid sinus at the level of L7. In order to confirm these findings and to fully evaluate the lesion, a computed tomographic (CT) examination of the lumbosacral junction was performed. The CT scan showed an anomalous fusion of the dorsal arch of L7 with an absence of the L7 spinous process, consistent with spina bifida (Figures 3 and 4). The dural cone appeared to protrude from the vertebral canal at this point and correlated with the previously identified skin depression. A few nerve roots of the cauda equina were visible in the vertebral canal at S1.

Figure 3.

Computed tomography (CT), sagittal view, showing the communication of the dural cone and the skin depression.

Figure 4.

Computed tomography (CT) examination, transverse view, showing the absence of the spinous process of L7 and the communication of the dural cone and the skin depression.

The dog was anesthetized and the lumbosacral region prepared in sterile fashion. An elliptical incision was made around the area of skin invagination and the sinus progressively isolated from the surrounding tissues, taking care not to penetrate the sinus during dissection. The sinus resembled a firm cylinder and was readily separated from the surrounding muscular plane as far as the dorsal vertebral arch of L7 (Figure 4). The dura mater was incised around the full circumference of the cylinder, adjacent to L7, freeing the tissue and allowing removal of the sinus. The nerves forming the cauda equina were visible at this point, and they were fewer in number than would be expected in a normal dog. After lavaging the surgical site, the 2 lateral leaves of the dura mater, which had remained following the resection of the sinus, were closed to reconstruct the dural cone and to prevent postoperative adhesion. A non-resorbable monofilament (Ethicrin 5/0, Ethicon, Aneau, France) was used to suture the dura mater and the muscular and skin layers were closed routinely.

Histopathological analysis demonstrated a cystic structure which included the dural sac (meninges) and nervous structures identified as the nerves of the cauda equina forming an adhesion with the site of skin invagination. This suggested a myelomeningocoele. A fibrous tract, several millimeters long and perpendicular to the skin surface connected the zone of cutaneous invagination with the terminal part of the myelomeningocoele, which was suggestive of a dermoid sinus.

The animal was followed for 6 mo after surgery. No lumbosacral pain was noted by the owners or by recheck clinical examinations at 15 d, 1 mo, 3 mo, and 6 mo after surgery. The degree of urinary and fecal incontinence worsened for several days after surgery, but a reexamination 15 d after the operation showed a return to the level of continence observed before the surgery.

Radiographs of the lumbosacral region were obtained 3 and 6 mo after the surgery. They indicated no morphologic alteration or sign of instability.

Discussion

To the author’s knowledge, this is the first case of a myelomeningocoele and a dermoid sinus-like lesion in a French bulldog. Dermoid sinuses are found on the dorsal midline and track ventrally in the underlying tissues. A classification has been established which embraces sinuses along the length of the vertebral column. Five types of sinuses are described: type I extend ventrally before adhering to the supraspinous ligament; type II are more superficial and attach to the supraspinous ligament via a fibrous band; type III comprise a superficial pouch without attachment to the supraspinous ligament; type IV extend further ventrally, penetrating the vertebral canal to adhere to the dura mater (7); and type V has been described more recently and reflects a true epithelial cyst (10,14). A suggested type VI has been described in a Swedish vallhound and a Burmese cat (20). The dermoid sinus described in this French bulldog could correspond to this 6th category with 2 differences: first, the fibrous band attached to the dura mater of a myelomeningocoele with the union through the spinal process defect and not in the spinal canal: the dural cone had protruded out of the spinal canal. Nervous structures identified as nerves of the cauda equina formed an adhesion with the site of skin invagination.

In the Rhodesian ridgeback, sinuses are predominantly found in the cervical region (9), the cranial thoracic region (7) and, more rarely, the sacrococcygeal region (5). In this breed, it is in the sacrococcygeal region that dermoid sinuses can communicate with the dura mater (23). In other breeds, dermoid sinuses with concurrent neurological deficits have been described in the cranial thoracic region (12,18,20) and in an intracranial location (24). A type IV dermoid sinus has been described in an English springer spaniel between L7 and S1 (17). In that case, the sinus crossed the intervertebral space. In our case, the sinus passed through an osseous defect which resulted from abnormal fusion of the vertebral arch of L7. Most recently, dermoid sinuses located on the nose and in the parieto-occipital region have been described in breeds other than the Rhodesian ridgeback (25–29).

Clinical signs appear when the sinus becomes infected (weeping) or in cases of communication with the dura mater (paraparesis, hyperesthesia). In these cases, surgical excision is recommended (30). Surgical treatment may not be required if the sinus is not responsible for clinical signs and is not connected to the dura mater (30). Cases with neurological deficits without treatment carry a guarded prognosis, as neurological function can continue to deteriorate because of further inflammation, infection, or cord compression due to accumulation of hair debris (15,17,20,30). Even if there is controversy about treatment of dermoid sinus, all dogs reported with neurological dermoid sinus revealed good outcomes after complete surgical treatment (4,9,12,15,17,20,30). In the presented case surgical excision was attempted because of clinical signs and suspected connection of the skin depression to the dura matter. A dorsal laminectomy is usually necessary to completely excise the sinus and break down the adhesions with the dura mater (8,17,18,20). In our case, the dermoid sinus passed through the unfused vertebral arch of L7, rendering a laminectomy unnecessary. In contrast to the case described in the English springer spaniel (17) with the type IV dermoid sinus between L7 and S1, no clinical deterioration occurred in the present case. The lumbosacral pain disappeared and the hindlimb ataxia improved. CVJ

Figure 5.

Blunt dissection of the sinus as far as the dura mater.