Introduction

Pneumothorax, or free air in the pleural space, can develop spontaneously, iatrogenically, or due to traumatic injury.¹ While spontaneous pneumothorax typically arises due to bullous emphysema,² traumatic pneumothorax results from penetrating or blunt injury to the thoracic wall or lung parenchyma. Treatment for pneumothorax in the dog is based on the suspected inciting cause. While the recommendation for spontaneous pneumothorax involves surgical intervention,^3,4 traumatic pneumothorax associated with blunt trauma is often managed non-surgically, with rest, periodic thoracocentesis, placement of a thoracostomy tube, and in rare instances, autologous blood patch pleurodesis.^5–8 Alternatively, in cases of traumatic pneumothorax caused by penetrating bite wounds, surgical exploration is recommended.^1,9

In the Northern United States and Canada, porcupine quilling has been described as a unique cause of penetrating traumatic pneumothorax in the dog.^10–12 The North American porcupine (Erethizon dorsatum) is native to deciduous and coniferous forests throughout these regions and is covered in sharp quills that are modified hairs.¹³ Porcupines are not reported to be aggressive; however, when threatened, they defend themselves with their quills by dislodging them and impaling their attackers.^14,15 The tips of these quills contain lubricated, backward-facing barbs that encourage forward movement into the body.^13,15 The most common complication associated with quilling injury in the dog is subcutaneous abscess formation, either septic or sterile in nature¹⁵; however, ease of quill penetration and adhesion can result in profoundly detrimental consequences, including pericarditis,^12,16 endocarditis,¹⁶ septic arthritis,¹⁷ chronic rhinitis,¹⁸ and renal,¹⁰ ocular,^19,20 cardiac^10,21 spinal cord,^10,22 and cerebral penetration.^10,23,24

Porcupine quills are most often removed with affected patients sedated or anesthetized, and it is not uncommon to miss quills, particularly in severe cases (eg, patients with > 100 quills). Quills are generally located by gentle palpation and then extracted with hemostats. In some cases, quills have already migrated under the skin or mucous membranes in the mouth, and in these cases, small incisions may be made to facilitate their removal. Ideally, quills are removed intact. Owners should be advised against cutting the quills at home, and quill removal should be performed as quickly as possible. The purpose of the study reported here was to review the characteristics, clinical course, and outcome of dogs with porcupine quilling–associated pneumothorax (PQAP).

Materials and Methods

Results

Preoperative imaging findings

All dogs had respiratory distress, tachypnea, or restlessness, alone or in combination. Thoracic radiography confirmed pneumothorax in all dogs; radiography revealed mineral linear opacities in multiple lung fields for 1 dog and a mass-like structure in the heart of another dog. Computed tomography was performed for 3 dogs with confirmed pneumothorax. The CTs of 2 dogs did not show any quills, whereas CT for the remaining dog revealed a thin, linear hyperdensity extending outside the pleura of the left lung lobe at the level of the twelfth thoracic vertebra, suggestive of the possibility of a porcupine quill in addition to pneumothorax and consolidation (Figure 1). A quill was subsequently located at this approximate location in surgery. One dog underwent abdominal ultrasonography for an unclear indication, and no abnormalities were documented.

View Full Size

Preoperative dorsal plane thoracic CT image of a 5-year-old castrated male mixed-breed dog approximately 5 days after quilling by a porcupine. Lesions are seen between the left cranial and caudal lobes. The dog’s right side is toward the left of the image. To help highlight the appearance of quills on CT, a specimen cup containing saline (0.9% NaCl) solution and quills is on the right side of the image, and a specimen cup containing only air is on the left.

Citation: Journal of the American Veterinary Medical Association 261, 4; 10.2460/javma.22.10.0451

• Download Figure
• Download figure as PowerPoint slide

Surgical procedure

Twenty-one dogs underwent an exploratory thoracotomy via median sternotomy. All dogs that were treated surgically underwent surgery during the next weekday; no dog had surgery performed off-hours. Nineteen dogs had quills identified within the thoracic cavity (Figure 2), while 2 dogs had no quills found intra-thoracically, but quills identified in the intercostal musculature. Fourteen of the 21 dogs underwent a partial or complete lung lobectomy, with 1 dog also undergoing pneumonectomy to remove diseased or nonviable lung parenchyma. Five dogs underwent quill removal via manual traction with no resection of lung tissue. For the dogs with records documenting locations of quills, most quills were in the cranial lung lobes, consistent with the common location of quills following a dog attack. Overall, there was a median number of 4 quills (range, 1 to 11 quills) surgically removed from the thorax. The number of quills removed was not recorded for 5 dogs. Two dogs underwent a pericardiectomy for quills within the pericardium, and 2 dogs underwent limb exploratory surgery for removal of palpable quills. The decision to pursue lung lobectomy, pneumonectomy, or gentle traction of quills with no lung tissue resection was at the discretion of the attending surgeon and was not clear from the available surgery reports why manual traction alone was not pursued. As a retrospective study, the costs of surgical care vary over time. However, the dogs treated surgically during the past 3 years had a total cost ranging from $3,897 to $7,659, with the higher costs reflecting longer surgery duration, longer hospitalization, and increased use of imaging.

View Full Size

Intraoperative image of dog that developed pneumothorax after attacking a porcupine. A quill protrudes from lung parenchyma. The dog is in ventral recumbency with its head toward the right of the image. Published with permission of Dr. Ray Kudej, DVM, PhD, DACVS, the copyright holder; all rights reserved. Individuals wishing to reproduce the image should contact Dr. Kudej (Tufts University, North Grafton, MA, Raymond.Kudej@tufts.edu).

Citation: Journal of the American Veterinary Medical Association 261, 4; 10.2460/javma.22.10.0451

• Download Figure
• Download figure as PowerPoint slide

Discussion

Porcupine quilling–associated pneumothorax appears to be an uncommon sequela to porcupine quilling. In the practices involved in this report, most dogs were initially treated at a different veterinarian or at home after their porcupine encounters, and only 1 dog returned to TCSVM with pneumothorax, 13 days after initial evaluation. No dogs initially treated at MVMC later returned with pneumothorax. The actual risk of developing a PQAP is unknown, as the vast majority of dogs are treated by local emergency hospital or their primary care veterinarian. At 1 hospital (TCSVM), there were 94 quillings reported in the electronic medical records in 2020, and 56 quillings in 2021. This hospital is located at the southern end of the porcupine range, and primarily sees quillings from central and western Massachusetts, eastern New York and southern New Hampshire and Vermont, despite seeing dogs for other diseases and injuries commonly from Connecticut, Rhode Island, and Eastern Massachusetts as well as the Cape and Islands. MVMC is in the heart of porcupine country and estimates 14 to 21 quillings per week during the season.

Consistent with prior reports, dogs of the present report were large-breed dogs or large mixed-breed dogs, and quilling injuries occurred mostly in the spring and fall months. As the porcupine is not aggressive and poorly visual, quillings typically occur around the head, thoracic limbs, and thorax as the dog attacks the porcupine (often by biting and tackling the large rodent) rather than attack by the porcupine.^10,13,20

Twenty-one of the dogs of the present report were treated with open thoracotomy to remove quills, damaged lung, or both. Minimally invasive thoracoscopic surgery has been described for removal of quills.²⁵ McCarthy reported²⁵ thoracoscopic removal of porcupine quills from the cranial mediastinum, pericardium, and cardiac wall of a Rottweiler. Five days later, the dog of that report²⁵ was returned with severe pneumothorax, and 9 more quills were removed thoracoscopically from the cranial lung lobes and mediastinum. While minimally invasive surgery decreases the degree of trauma, obvious limitations include decreased visualization and the risk of leaving quills behind, necessitating subsequent surgical procedures.

Recommended treatment of pneumothorax in dogs reflects the underlying cause of pneumothorax. In dogs with primary spontaneous pneumothorax, associated with a bulla or bleb, surgical exploration has been associated with a better outcome than medical management alone.⁴ In dogs with traumatic pneumothorax from blunt trauma (motor vehicle accident), medical treatment, including rest, periodic thoracocentesis, chest tube placement, or autologous blood patch pleurodesis, alone or in combination, is most often recommended, while in penetrating trauma (bite wounds), surgical exploration is advised due to potential contamination of the thoracic cavity.

Porcupine quilling–associated pneumothorax represents a unique form of a penetrating traumatic pneumothorax as the quills contain natural anti-microbial properties²⁵ and surgical exploration is indicated to limit further trauma from the quills, rather than to treat for potential infection. Four of the dogs were treated with medical treatment alone, with apparent resolution, and 2 dogs underwent thoracotomy without identification of intrathoracic quills but with subsequent resolution of the pneumothorax, presumably due to the lungs healing.

Unfortunately, diagnostic imaging modalities are of limited utility in preoperative identification of quills or in the dogs reported here, establishing an indication for a thoracotomy.^{10,12,18,21,22,24} Thoracic radiography is useful primarily for confirmation of a pneumothorax rather than quill confirmation. CT was accurate in identifying quills in 1 of 3 affected dogs. As the planned approach in all dogs was a median sternotomy, it was unclear whether preoperative CT would provide additional information. However, it may be considered at the clinician’s discretion. There are multiple case reports describing different imaging modalities with varying levels of success in identifying quills.^10,18,22,24 Flesher et al¹⁰ describe a Boston Terrier in which migrating quills could not be detected with the use of CT or MRI. Captanian and Palma¹⁹ describe a Rhodesian Ridgeback in which CT showed a normal nasal cavity; however, subsequent rhinoscopy identified 3 porcupine quills. Sauvé et al²⁴ report on the use of CT in diagnosing an intracranial intra-axial quill foreign body in a Golden Retriever, and Le Roux et al²² confirmed the diagnosis of a quill in the spinal cord of a Jack Russell Terrier with the use of ultrasonography, MRI, and CT. The accuracy of advanced imaging in identifying quill foreign bodies is likely multifactorial, dependent on quill architecture, quill location, contrast differences of surrounding tissues, and imaging modality chosen. Our findings that intrathoracic quills were found in 19 of the 21 dogs that underwent thoracotomy supports a high likelihood of finding intrathoracic quills in dogs with PQAP. If a median sternotomy is chosen, this will permit for exploration of the entire thorax as well as gentle palpation to attempt to identify quills.

Interestingly, while the median time lapse from quilling to pneumothorax was 6 days, it ranged from 1 to 60 days after the quilling, suggesting that vigilance should persist for at least 2 months after a quill exposure. All 25 dogs had quill removal immediately after the incident, either by the owner or a veterinarian, thus the quills responsible for the pneumothorax likely migrated quickly after quilling. The speed at which a porcupine quill can migrate is unknown and likely reflects the tissue characteristics surrounding the quill, the size of the quill, and the activity of the dog.

Limitations of the present study were similar to all retrospective studies, namely a smaller case number over a number of years. The medical records were occasionally sparse, and the rationale behind decisions about case management were dependent on clinician preference and not always justified or clear.

Porcupine quilling–associated pneumothorax is likely an uncommon sequela of porcupine quilling. Surgical management has a high likelihood of a good outcome, although a small number of dogs may recover under successful medical management. Dogs in areas where porcupines are endemic should be prevented from roaming and if a quilling occurs, the owners and veterinarian should monitor the dog closely for clinical signs consistent with pneumothorax and be aware of the possibility of quill migration.