Abstract
An 11-year-old neutered female domestic shorthair indoor cat was presented to our hospital for treatment of a left-sided rostro-temporal basal meningioma. Focal seizures in the facial muscles had been observed sporadically for 1 year. Two weeks prior to presentation the cat had developed generalised seizures and was treated with symptomatic anticonvulsive treatment. Focal facial seizures, especially on the right side, persisted after medical therapy. From the computed tomography scan, a basal meningioma was suspected by the treating veterinarian. A left-sided suprazygomatical temporobasal approach to the zygomatic arch was chosen because it causes less soft tissue damage. After craniotomy, durotomy and gentle dorsal retraction of the left piriform lobe, the meningioma was removed. Postoperative magnetic resonance imaging confirmed complete excision of the tumour. One day after surgery the cat was alert and a left-sided facial nerve palsy was noticed. Otherwise the neurological examination was normal. Anticonvulsive and eye moistening therapy was continued for 3 months. Six months after surgery the cat was clinically normal without any recurrence of seizures.
An 11-year-old neutered female domestic shorthair indoor cat was referred to our hospital with a history of sporadic focal facial seizures over a 12-month period, maturing to generalised seizures 2 weeks prior to presentation. A symptomatic treatment using diazepam (10 mg/kg) initially and phenobarbital (2 mg/kg bid PO) was instituted. Subtle focal seizures remained, especially on the right side of the face. A computed tomography (CT) examination of the brain had been performed by the referring veterinarian prior to admission. A tentative diagnosis of rostro-temporal left-sided basal meningioma was made (Fig 1) and the cat was referred to our institution for further treatment.
Fig 1.
Three-dimensional reconstruction (shaded area) of the preoperative CT-images. The extracranial soft tissue structures have been removed. By removing the bone (zygomatic arch, parts of the temporal bone) at the surgical window, it is possible to demonstrate the position of the meningioma (red) in relation to the brain (violet).
The presented cat was irregularly vaccinated, dewormed, and feline leukaemia virus-negative. Moderate obesity was the only abnormality found during the general physical examination. The owner reported that the cat had become irritable over the last few months. Manipulation led to excitation and slight aggression, making the neurological evaluation difficult. The menace response was bilaterally reduced. Other cranial nerves were normal and no further neurological abnormalities were detected. No focal seizures were observed on initial examination. The neuro-anatomical localisation was consistent with a forebrain intracranial lesion. Differential diagnoses included neoplasia, vascular, metabolic and/or inflammatory processes. A complete blood count, serum biochemistry panel and thoracic radiographs were performed. All examinations were normal, except for a slight hyperproteinaemia (80.2 g/l, reference range 56–78 g/dl).
A magnetic resonance imaging (MRI) scan was performed shortly before surgery to evaluate the brain tissue and the meninges in order to rule out the presence of an additional lesion in the case of meningioma. The anaesthesia was induced using a combination of medetomidin (Domitor: Orion, Finland, 5 μg/kg BW IV), ketamin (Ketasol; Graeub AG, Switzerland, 2 mg/kg BW IV) and propofol (Diprivan; Astra Zeneca, USA, 4 mg/kg BW IV), followed by inhalation anaesthesia with isoflurane (Isoflurane; Abbott, Wiesbaden, Germany) and oxygen.
An MRI scan was performed with a 0.3 Tesla permanent magnet MRI unit (Hitachi AIRIS II; Hitachi Medical Systems; Düsseldorf, Germany). Preoperative sequences included a transverse FSE T2 and a dorsal FE 3D MPR T1–weighted sequence (high resolution gradient echo, plain and contrast-enhanced). Gadodiamide (Omniscan; GE Health Care, Munich, Germany) was administered intravenously in a dosage of 0.15 mmol/kg body weight. An extra-axial mass was seen in the left ventral neurocranium. It extended from the level of the rostral bulla to the orbital fissure, distorting and compressing the left piriform lobe and thalamus (Fig 2a).
Fig 2.
Dorsal contrast-enhanced FE 3D MPR T1 weighted images at the level of the tumour. The rostral is at the top; the right side is shown on the left of the image. (a) Pre-surgery: The contrast-enhanced meningioma can be easily delineated as a hyperintense (bright) structure at the left rostral brain. (b) Post surgery, no residual tumour can be seen. The defect is filled by material isointense to the brain (haemorrhage). The surgery site can be identified by the irregular structure of the masseter muscle and bone on the left side (compare with the muscle on the right side).
Methylprednisolone sodium succinate (Medrate solubile; Pfizer, Karlsruhe, Germany, 30 mg/kg BW IV) and mannitol (Braun-melsungen; Melsungen, Germany, 0.5 g/kg BW IV over 20 min) were administered preoperatively. Prophylactic antimicrobial therapy with cefazolin (Kefzol; Medica, Aesch, Switzerland, 25 mg/kg BW IV) was also administered.
Anaesthesia was maintained with 1.5–2% isoflurane (Abbott; Wiesbaden, Germany) and oxygen. Mild mechanical hyperventilation (end-tidal CO2 3–3.5%) was applied. Intraoperative analgesia was provided with lidocain (Xylesin; Amino AG, Switzerland, 0.03 mg/kg/min constant rate infusion (CRI)) and fentanyl (Janssen; Neuss, Germany, 0.05 mg/kg CRI). Lactated Ringer's solution (3 ml/kg/h IV) was administered throughout surgery. Monitoring included electrocardiography, blood pressure (BP) and end-tidal CO2 concentrations.
The head was shaved from the eyebrows to the level of C1 on the left side, scrubbed with chlorhexidine and disinfected with alcohol and povidone–iodine. The cat was positioned in right lateral recumbency with the head slightly tilted (20°) to the left and elevated, taking care to maintain airway patency. A straight 2 cm vertical skin incision was performed dorsal to the zygomatic bone. Small subcutaneous bleeding vessels were cauterised with bipolar microforceps. The platysma was incised vertically. The superficial temporal nerve and the rostral auricular nerve were retracted caudally and the zygomatic branch of the facial nerve cranially. After incision of its zygomatical attachment, the caudal margin of the temporal muscle was elevated from the temporal bone in a blunt fashion. A 1.5-cm large craniotomy/craniectomy was performed dorsally to the caudal attachment of the zygomatic arch. The medial meningeal artery was identified and ligated. After durectomy the piriform lobe was slightly elevated with microsurgery swabs (Ethikeil; Ethicon, Norderstedt, Germany) and ocular sticks (Pro-Ophta; Lohmann Rauscher, Rengsdorf, Germany) placed under the brain in order to allow better exposure of the tumour. The tumour was first internally decompressed using a single-window technique: the visible surface of the tumour was fenestrated and the centre of the tumour enucleated using tumour forceps through this window. The tumour margins could then be carefully dissected away from the brain tissue favoured by a good cleavage plane. After removal of all blood clots and copious lavage of the craniotomy site with saline solution, the operation site was closed by readaptation of the caudal part of the temporal muscle to its zygomatical attachment, and closure of the platysma, the subcutaneous tissue (PDS 4–0, Ethicon, Norderstedt, Germany) and the skin (Prolene 4–0, Ethicon, Norderstedt, Germany).
A postoperative MRI revealed complete gross tumour removal (Fig 2b). No signs of peritumoral oedema as a consequence of iatrogenic parenchyma manipulation and removal of the space-occupying lesions were seen on T2-weighted sequences.
Postoperatively the cat was kept in an oxygen box for 12 h. Temperature, pulse and respiratory rate, capillary refill time, blood pressure, auscultation, control of neurological status and micturition were monitored. Postoperative analgesia was provided with fentanyl (Janssen; Neuss, Germany, 0.02 mg/kg BW CRI) for the first 12 h, and later with buprenorphine (Temgesic; Essex, München, Germany, 0.01 mg/kg BW SC q 8 h). Lactated Ringer's solution (2 ml/kg/h CRI) was administered for 24–36 h. The cat received cefalexin (Cefaseptin mite; Chassot, Ravensburg, Germany, 25 mg/kg BW PO q 12 h) for the first postoperative week, and phenobarbital (Aphenylbarbit; Streuli, Switzerland, 2 mg/kg BW PO q 12 h) was progressively discontinued over 3 months postoperatively. The histopathological and immunohistochemical diagnosis was a fibrous meningioma.
Neurological examination was normal on the first day after surgery except for a facial nerve palsy. The follow-up examinations were performed by the referring veterinarian. Six months after surgery the facial nerve palsy had completely resolved. The recurrence of seizures has not been observed since surgery and the cat has remained neurologically normal.
Meningiomas are the most common primary intracranial tumour in cats. 1–3 They initially grow slowly outwards into the arachnoidal spaces and onto the brain, and about 50% of affected cats do not manifest any clinical signs. 1,4 MRI is the imaging modality of choice for detection of brain tumours and provides superior resolution of intracranial lesions compared to CT. The sensitivity in detecting brain tumours in cats is approximately 98%. 5 Meningioma is the most common tumour overall (58%) and the most common extra-axial tumour (83%) in cats. Therefore, the odds are high that an extra-axial mass in a cat is a meningioma. 2
The base of the skull has been described as a predilection site for meningiomas (olfactory, sphenoid, suprasellar, foramen magnum, pontocerebellar angle, tentorium cerebelli). However, to the author's knowledge surgical treatment of a temporal basal meningioma has not yet been described in cats. 6,7
Most craniotomies are performed with the patient in sternal recumbency. Care must be taken not to apply pressure to the jugular veins, thus preventing cerebral venous congestion, impaired venous drainage and oedema which increase intracranial pressure. The described modified approach was performed in lateral recumbency with a head tilt of 20° towards the side of the lesion, avoiding potential risks associated with positioning.
Surgical approaches to intracranial lesions are based on the location, extent and nature of the lesion and the purpose of surgery (removal, biopsy, decompression). Good exposure of the lesion is a key aspect contributing to successful intracranial surgical outcome. 8 Limited approaches make exposure of the lesion difficult and increase the risk of iatrogenic brain damage from excessive manipulation of the brain. 9 Rostrotentorial craniotomy/craniectomy exposes the cerebrum. It can be modified to allow increased exposure of the ventral aspect of the cranial vault by exposing and excising the zygomatic arch. 10 However, such extensive approaches, necessitating complete ventral reclination of the temporal muscle, are invasive and may lead to severe injury of the masticatory muscles. Furthermore, postoperative discomfort after such surgeries have not been evaluated in cats. In general, ventral exposure of the skull below the zygomatic arch is difficult and the exposure is inadequate for removal of masses. 8 The approach described remained dorsal to the zygomatic arch and preserved the cranial and dorsal integrity of the temporal muscle. One drawback of the method was the retraction of the facial nerve which, in our case, lead to a postoperative reversible facial paralysis.
Postoperative disturbance to the function of the piriform lobe (seizure, loss of smell and taste) as a consequence of surgical dorsal retraction was not observed clinically. The single-window technique was used to prevent iatrogenic damage to the surrounding brain tissue during cleavage and excision of the meningioma. 11 The most accessible area of the tumour surface was opened and the centre of the tumour enucleated using tumour forceps through this window. The first phase of the single-window technique permits reduction of the tumour mass and requires very little space. In fact, it creates the space necessary to dissect and free the capsule or pseudocapsule from the surrounding tissue and to remove the remainder of the tumour piece by piece from the wound. Finally, copious lavage of the surgical site stops bleeding from small vessels and helps to remove floating tumour cells.
As resection was judged as macroscopically complete on the basis of a postoperative MRI, the prognosis should be good and survival should be significantly prolonged after surgical intervention. 12,13 Median postoperative survival time after surgery is 685 days (23 months) compared to 18 days for cats that are treated medically. 14 Survival may be prolonged with radiotherapy 15,16 but the owner declined radiation treatment because of the large distance to the nearest veterinary radiotherapy unit.
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