Paramedian Submandibular Approach for Removal of Foreign Bodies in the Pterygoid Muscle in Two Dogs
ABSTRACT
The purpose of this report is to document a unique location of an oropharyngeal foreign body, diagnosed via contrast computed tomography (CT), as well as a novel surgical approach to the pterygoid muscle region. Oropharyngeal foreign objects are an uncommon but potentially serious disease that can lead to chronic abscessation and pain. Two dogs were presented with chronic complaints, including pain and inability to fully open the mouth for a 1 yr and 5 mo duration, respectively. There was no history or evidence of skin sinus or submandibular/cervical swelling on physical examination of either dog. Both dogs had normal oropharyngeal anatomy with the exception of an asymmetric contrast-enhancing lesion within the pterygoid muscle on CT imaging. As there were no gross abnormalities visible during surgery, the use of contrast CT was vital in order to isolate the focus of infection. A paramedian submandibular approach was used to explore this region, and in both cases, foreign material was successfully removed with subsequent resolution of clinical signs. The dogs were immediately free of clinical signs and showed no recurrence for at least 8 and 17 mo after the exploration, respectively. A novel surgical approach is described to remove oropharyngeal foreign objects and necrotic debris within the pterygoid muscle.
Introduction
Traumatic injury to the oropharynx is an uncommon but serious condition potentially leading to chronic abscessation and pain.1,2 The sublingual area is the most common region penetrated by foreign bodies (41%); other areas affected include the lateral pharyngeal wall (24%), tonsillar region (18%), and rostral and dorsal pharynx (12% and 6%).1 The most common method of diagnosing oropharyngeal foreign bodies is via sedated oral examination as well as cervical radiographs to look for pharyngeal/esophageal perforation and subsequent subcutaneous emphysema. Fistulography has also been utilized, but its value in localizing foreign bodies is inconsistent.2,3 Modalities such as ultrasonography, computed tomography (CT), or MRI may be necessary in chronic cases in which a wound in the oral cavity is not apparent in order to help the surgeon localize the nidus of inflammation.4,5–10 An oral approach has been utilized to access retropharyngeal abscesses for drainage; however, this approach often does not provide adequate visualization to allow the surgeon to be confident that the inciting foreign body has been completely removed. This can result in recurrence or persistence of clinical signs postoperatively.1,2,4 The purpose of this report was to describe two dogs with oropharyngeal foreign bodies present in an unusual location and the use of a novel surgical approach used to treat them.
Case Reports
Case Report 1
A 6 yr old male castrated Weimaraner was presented to his primary veterinarian for a 1-yr history of pain when chewing and inability to fully open his mouth (trismus). During a hunting trip, the patient sustained a laceration injury below the left ear. One month following this trauma, he began to have pain when chewing and had a fever on physical examination. A sedated oral examination was performed; no abnormalities were visualized in the oropharyngeal cavity, but a grass awn was removed from the ear canal. According to the owner, the dog was treated with a course of an unknown antibiotic, and he apparently improved for approximately 2 mo. At this time, the clinical signs recurred, and he was given a different antibiotic. The dog improved temporarily, but the signs recurred. The referring veterinarian administered methylprednisone at an unknown dose or length of treatment. The medication was discontinued since the dog experienced gastrointestinal side effects. The dog was subsequently referred to Colorado State University.
On initial physical examination, the dog was normothermic, and the left submandibular and superficial cervical lymph nodes and the parotid salivary gland were mildly enlarged. There was mild atrophy of the masseter muscles bilaterally. The patient was able to eat kibble but exhibited pain when chewing, and he was not able to fully open his mouth. Differential diagnoses included foreign body or abscess in this area, masticatory myositis, neoplasia, and temporomandibular joint disease. The diagnostic and treatment plan was to perform an oral examination and advanced imaging with CT scan under general anesthesia. Preanesthesia cell blood count revealed a mild lymphopenia of 0.7 thousand (1.0–4.8), a mild monocytosis of 1.3 thousand (0.2–1.0) and a mild anisocytosis with red blood cell distribution width 16.0 (12.0–15.0). On serum biochemistry analysis, the dog had a mild hyperglycemia of 119 (70–115) and a mildly elevated chloride of 119 (108–118). Serum 2M titers for masticatory myositis were negative. An oral examination did not reveal any abnormalities; CT of the skull and cervical soft tissues with intravenous contrast administration was performed. On CT precontrast images, the left medial pterygoid muscle was enlarged with multiple small hypoattenuating structures within the muscle body. Iohexol was administered intravenously at a standard dose of 60 mL (350 mg/mL concentration) over several minutes. After contrast administration, multiple rim enhancing hypoattenuating pockets were present within the medial pterygoid muscle. The CT diagnosis was left medial pterygoid abscessation and myositis (Figure 1). Following this imaging procedure, the owners elected to delay surgery, so the patient was placed on a course of clindamycin and tramadol for 14 days prior to surgery. At recheck, the dog still had similar clinical signs, so the owners elected surgical exploration of the retropharyngeal area. The patient was premedicated for anesthesia with 0.05 mg/kg morphine, 0.03 mg/kg acepromazine, and 0.03 mg/kg atropine subcutaneously; induced with 5.2 mg/kg ketamine, 0.1 mg/kg midazolam, and 1.3 mg/kg propofol; and maintained under a surgical plane of anesthesia using isoflurane and oxygen. A left paramedian submandibular approach was used to gain access to the pterygoid muscle (See Figure 2 for a description of the surgical approach). After exposure of the pterygoid muscle, no obvious gross abnormalities were found. Using CT image guidance, and measuring rostrally from the hamulus, a hemostatic forceps was used to bluntly enter the medial pterygoid muscle. A thickened and discolored capsule was encountered deep within the middle of the muscle. Upon penetrating the capsule, a cavity was detected, and macerated plant material was removed. The area was thoroughly lavaged, a sample for culture was obtained, and the wound was closed primarily. Due to the unavoidable contamination of the surgical site and the dead space in the wound, a closed suction draina was placed before closure. The culture revealed light growth of Corynebacterium species, Prevotella species, and moderate growth of Streptomyces species. Postoperative pain was controlled via oral tramadol (2.6 mg/kg q 8 hr) and 2 mg/kg carprofen q 12 hr, and 7.85 mg/kg clindamycin q 12 hr was continued for another 7 days. The bacteria present were found to be susceptible to macrolide antibiotics, thus clindamycin was continued. Four days after surgery, the patient removed the drain prematurely. The drain exit site sealed, and minor fluid accumulation occurred in the ventral cervical area. Fluid deep to the incision was sampled via fine needle aspiration, and bacterial culture showed no growth. The fluid accumulation resolved spontaneously, and the patient had complete resolution of clinical signs, but the owner reported that the dog had pain during chewing 4 mo postoperatively, which resolved with carprofen therapy alone, and no further complications have been reported 17 mo postoperatively.
Citation: Journal of the American Animal Hospital Association 53, 4; 10.5326/JAAHA-MS-6430
Citation: Journal of the American Animal Hospital Association 53, 4; 10.5326/JAAHA-MS-6430
Case Report 2
A 7 yr old male castrated Labrador retriever mix was presented to Colorado State University for a 5 mo history of pain and trismus. Previous treatments included antibiotic therapy with clindamycin and then enrofloxacin and metronidazole, with no clinical improvement. Therapy with prednisone was initiated after no response to antibiotic therapy, and this also resulted in no improvement. A serum 2M-antibody test was subsequently submitted to rule out masticatory myositis, and the result was negative. On physical examination, the dog was unable to voluntarily open his mouth fully even following sedation. The oral cavity was examined under sedation, and a small amount of brown exudate was observed at the caudal aspect of the oropharynx on the right side, but no puncture wound was evident. Preanesthesia diagnostics revealed a mildly decreased hematocrit at 39% (40–55%), and the serum biochemistry was within normal limits. Thoracic radiographs were normal. The patient was premedicated for anesthesia with 0.5 mg/kg methadone, induced with 2 mg/kg propofol and 0.1 mg/kg midazolam, and maintained under a surgical plane of anesthesia using isoflurane and oxygen. CT of the skull and cervical soft tissues with intravenous contrast administration was performed as previously described in case 1. On CT precontrast images, an oblong hyperattenuating structure was identified within the right medial pterygoid muscle (Figure 3). After intravenous contrast administration, slight peripheral rim enhancement with internal hypoattenuating material surrounded this hyperattenuating structure. Additional ill-defined enhancement followed the adjacent fascial planes and soft palate. CT diagnosis was an intramuscular foreign body with abscessation/granuloma formation and associated pterygoid myositis. The same approach was used as described in case 1, with the exception that the approach was on the opposite side (Figure 2). Similar to the first dog, on gross examination, the surface of the medial pterygoid muscle appeared normal, and the same technique was used to dissect into the diseased muscle. Grass and other organic foreign material were removed, and necrotic tissue was debrided bluntly from the abscess cavity (Figure 4). The area was thoroughly lavaged, a bacterial culture was taken, and the wound was closed primarily. A culture revealed a heavy growth of Bacillus species, Pasteurella multocida, Streptococcus beta haemolytica, and S non-haemolytic. Postoperative pain was controlled via oral tramadol at 3.1 mg/kg q 8 hr and carprofen at 2.1 mg/kg q 12 hr. A 10-day course of amoxicillin/clavulanic acid was prescribed, and the owners were asked to apply cold compresses to the region for 3 days. The patient healed with no complications, and sutures were removed in 14 days. At that time, the dog could open its mouth widely with no evidence of pain. As of this writing (5 mo posttreatment), the patient has not had any recurrence of the original clinical signs.
Citation: Journal of the American Animal Hospital Association 53, 4; 10.5326/JAAHA-MS-6430
Citation: Journal of the American Animal Hospital Association 53, 4; 10.5326/JAAHA-MS-6430
Discussion
Chronic pain on opening the mouth and trismus are clinical signs that have a variety of possible etiologies. Causes include local or generalized muscular diseases, such as masticatory myositis, polymyositis, or muscular dystrophy. Conditions of the jaw or surrounding boney regions can cause similar signs; examples include severe dental disease, temporomandibular joint osteoarthritis, dislocation of the jaw, craniomandibular osteopathy, neoplastic conditions, and aggressive tympanic bulla lesions. Infectious organisms can result in polymyositis, and tetanus infection can cause trismus. Masses within the oral cavity or surrounding musculature can result in pain on movement of the mandible.12 In young dogs, especially those that chew on sticks or sharp plant material, oropharyngeal foreign bodies are a relatively common occurrence.1 Foreign material and retrobulbar abscesses or abscesses of the muscles surrounding the jaw may lead to trismus and pain. A complete history and physical examination can help to guide the diagnostic plan, but advanced diagnostics including serology and imaging may be necessary. In these cases, CT imaging was extremely helpful in isolating the nidus of infection and to help guide intraoperative dissection.
The most common areas for foreign objects to lodge in the oropharynx include the sublingual area and the lateral pharyngeal wall; peri-esophageal abscessation is also a relatively common phenomenon.1 To the author's knowledge, these are the first documented cases of foreign objects lodged exclusively in the medial pterygoid muscle. The medial pterygoid muscle lies along the medial aspect of the mandible; it originates on the pterygopalatine region of the skull and inserts on the medial aspect of the mandible at the angular process. The pterygoid muscle functions to elevate the mandible and, in unilateral contraction, displace it medially to aid in mastication.13 In the cases described, pain was most apparent when opening the mouth and with mastication of food. This coincides well with pain on stretching and contraction of the inflamed pterygoid muscle, respectively.
Organic foreign material can be extremely difficult to differentiate via advanced imaging from surrounding soft tissue structures.5 The use of contrast CT was invaluable in these cases and served to highlight the inflammation and interstitial fluid accumulation associated with the foreign material. Contrast enhancement occurs in tissues with increased blood flow, so this enhancement is expected in tissues that are inflamed or through neovascularization associated with neoplasia. Contrast enhancement can highlight fistulous tracts, which are chronically inflamed, and highlighting these tracts can help guide the surgeon to the foreign body or associated granuloma/abscess for a more definitive location.14 The enhancement focused in the medial pterygoid musculature in these two cases, which allowed for better localization and determined surgical approach chosen in these cases. In case 2, the foreign body was visible on CT and was hyperattenuating; however, in case 1, the foreign body itself was not visible. This can occur due to the composition of the foreign material present.5 Nevertheless, this imaging modality was critical to isolation of the nidus of the infection in these two cases. In case 1, Prevotella were present. Prevotella species predominate in periodontal disease and periodontal abscesses but have also been isolated from infections of the respiratory tract as well as other areas.11
The majority of foreign objects lodged in the oropharynx occur in a location where an oral approach may be utilized, particularly if a portion of the retained foreign body extends into the oral or pharyngeal cavities.1 Foreign objects further caudal, or those where there is no apparent penetration site in the mouth, are often approached using a ventral midline, cervical approach. The lack of localization of the penetration site and the caudolateral oropharyngeal location of the foreign bodies in these two cases made an oral approach difficult. This poorly exposed area could not be easily explored via an oral approach. The approach used in this case report is similar to one utilized to access the polystomatic portion of the sublingual salivary gland.15 The use of this technique allowed access to the medial pterygoid muscle with adequate visualization and the ability to thoroughly debride the abscess and provide for drain placement afterward. It is important to note that in both of these cases the surface of the medial pterygoid muscle appeared grossly normal during exploration, and only when the muscle belly was penetrated were foreign material and necrotic debris discovered. Therefore, reliance on our CT findings was imperative for accurate localization and to reduce unnecessary dissection.
While the visualization in this area is much improved with the described approach compared to an oral approach, exposure is still limited. In addition to limited space, there are important structures in this area that must be protected during deep dissection. Superficially, there is the sublingual branch of the facial nerve, and then more deeply, branches of the hypoglossal nerve as well as the lingual vein are encountered. The polystomatic portion of the sublingual salivary gland lies just superficial to the medial pterygoid muscle, so care must be taken not to damage this gland or associated duct. After penetration through the myelohyoideus muscle and widening the incision to increase exposure, great care must be taken to avoid disruption of the thin oral mucosa lying just medial to the muscle.
Conclusion
These cases highlight the utility of contrast CT to help diagnose, locate, and remove foreign bodies from the pterygoid muscle region. A limited paramedian submandibular approach is described and was used to successfully remove foreign bodies lodged in the pterygoid muscles.
Computed tomography transverse plane postcontrast image (Window Width 365 Window Level 119). Note the heterogenous and peripheral contrast enhancement in the left medial pterygoid muscle (white arrow).
Surgical approach demonstrated on a cadaver: (A) An approximately 8 cm paramedian incision was made through the skin of the medial aspect of the ramus of the mandible extending to the angular process. The incision was continued deeper through the platysma muscle until the myelohyoideus (MH) and digastricus (DG) were visible. (B) Deeper dissection continued along the medial aspect of the mandible (M), taking care to avoid penetration through the mucosa into the oral cavity. (C) The myelohyoideus muscle was incised longitudinally, exposing the medial pterygoid (PT) muscle lateral to the mucosa of the oral cavity and deep to the polystomatic portion of the sublingual (sub) salivary gland. (D) The abscessed area was localized by palpating the hamulus of the pterygoid bone and measuring from this landmark to the affected area, using computed tomography images as a guide. A stab incision can be seen into the medial pterygoid muscle. This technique resulted in exposure of abscessed and necrotic muscle and debris. DG, digastricus; M, mandible; MH myelohyoideus; PT, pterygoid; sub, sublingual.
Computed tomography transverse plane precontrast image. Note the heterophogenous foreign material present within the right medial pterygoid muscle.
Intraoperative photograph of case 2 showing foreign material within the medial pterygoid muscle.
Contributor Notes
