Findings:
- The nasofrontal suture is mildly to moderately widened (yellow circle). Extending along the entire margin of the frontonasal suture, from the left to the right orbit, and involving the nasolacrimal sutures, bilaterally, there is a moderate amount of ill-defined, irregular periosteal proliferation, which is most severe near dorsal midline. Additionally, there is irregular osseous proliferation and moderate focal osteolysis of the nasolacrimal canals, bilaterally at the level of the orbits, most severe on the right (blue arrow).
- At the level of the nasofrontal suture, moderate to severe, the mucosa covering the left dorsal concha is focally thickened with mild contrast enhancement (yellow arrow). Mild to moderate soft tissue thickening is present along the length of the nasofrontal and nasolacrimal sutures.
- Bilaterally in the parotid salivary glands, there are numerous, multifocal small to medium sized, well-defined and hyperattenuating soft tissue nodules with rounded lobular margins (pink arrows). Within the lateral aspect of one of these nodules, at the level of the left jugular process, there is focal punctate mineralization. At the base of the right pinna, just cranial to the right external ear canal, a round, well-defined soft tissue attenuating nodule, with a mineral attenuating central region, is identified (green circle).
- Bilaterally, the wall of the horizontal ear canal is mildly mineralized.
- In the central aspect of the nuchal ligament, just dorsal to C1, mild mineralization is present.
- Mild osteophyte formation is present on the axial aspect of the mandibular condyles, at the level of the temporomandibular joints, bilaterally.
- There is mild periapical alveolar bone lysis and sclerosis surrounding multiple maxillary and mandibular premolar and molar teeth.
Conclusions:
- Extensive osseous proliferation of the frontonasal and nasolacrimal sutures, some of which has aggressive features, involving the caudoproximal aspect of the nasolacrimal canals. The primary differential is nasofrontal suture exostosis with possible, secondary nasolacrimal duct obstruction. A component of osteomyelitis, secondary to the reported trauma should be considered.
- Extensive, bilateral parotid nodules within the laryngeal region, one of which is mineralized. Neoplasia, such as melanoma, is considered primarily. The mineralized nodule rostral to the left ear base could also represent a dentigerous cyst.
- Mild bilateral temporomandibular osteoarthritis.
- Mild, multifocal maxillary and mandibular periodontal disease.
- Mild nuchal ligament dystrophic mineralization.
A little bit more…
Suture line periostitis (suturitis)
- Thought be most likely caused by trauma; however, given that a large portion of horses do not have a history of witnessed trauma, other etiologies, such as excessive masticatory forces could contribute to its development (Dixon et al., Klein et al.).
- A firm swelling in the frontonasal region is most commonly identified on physical examination and is usually non painful. Most often occurs just rostral to the eyes and may be linear or V-shaped (Dixon et al., Klein et al., Manso‐Díaz et al.).
- Fine boned horses, such as Thoroughbreds, may be at a higher risk (Dixon et al.)
Dixon et al.
- Progression of disease:
- Initially, nasofrontal suture line is widened and noncalcified.
- Within weeks, osseous proliferation (e.g. exostoses) develop along the margins of the suture lines, on each side of the suture gap.
- Gradually, the degree of exostosis increases and may bridge the suture line, expanding on both side of the suture (externally and internally). Compression of the nasolacrimal duct may occur in some cases.
- Over time, the exostosis remodels, decreases in size and can resume a normal contour. This often takes 12–18 months at the level of the nasofrontal suture and may only take a few months if involving the nasolacrimal suture.
- Radiography is most commonly used to identify suture line periostitis (Dixon et al.) and may be characterized as follows:
- Irregularity of the affected suture line with variable degree of osseous proliferation +/- overlying soft tissue swelling.
- Best for evaluation of the nasofrontal suture (limited assessment of the nasolacrimal suture).
- Dacryocystorhinography may be considered to evaluated for nasolacrimal duct obstruction.
- Computed tomography is the preferred modality but is often not necessary given the left limited nature of the disease.
- No treatment is required, unless if the lesions persist for >12 months (surgical stabilization of the suture line may be considered) (Dixon et al., Klein et al., Manso‐Díaz et al.).
- Some cases will develop bacterial infections of the sutures and need treatment (Dixon et al.). Surgery is indicated with sequestra formation.
affected nasofrontal suture may be considered as illustrated here (Klein et al.)
Melanomas:
- Most common neoplasm in the horse (representing 3-15% of equine tumors) (Dixon et al.).
- melanomas are frequently identified in the head region, particularly affecting the parotid salivary glands, eye and eyelids, ears, guttural pouches, paranasal sinuses, lymph nodes, and various cutaneous sites (Dixon et al.). May also be seen in other places, such as the perineal region/tail base, lips, and prepuce (Dixon et al.).
- Grey horses are genetically predisposed.
- Melanomas may be heavily pigmented to nonpigmented (amelanotic). Most equine melanomas are pigmented (Dixon et al.).
- Distinct computed tomographic features are been described (Dixon et al.):
- Well-defined, predominantly homogenous nodules/masses (~113.5 HU) which are hyperattenuating compared to the regional musculature on pre-contrast CT.
- May contain variable degree of mineralization (1/4 of lesions).
- Tumors will often progress over time and no good treatment options have been proposed to date (MacKay).
- Local control via surgical excision and/or intralesional chemotherapy (possibly with adjunctive hyperthermia or electroporation) may be considered.
- Systemic therapy, such as immunomodulators and vaccines, have no proven efficacy but may be considered (MacKay).
References:
- Dixon, P. M. “A review of swellings of the frontal region of the equine head.” Equine Veterinary Education 26.7 (2014): 365-371.
- Klein, Linda. Clinical, radiographic and histological findings, treatment and outcome in 15 horses with suture periostitis: a case series. Diss. University of Zurich, 2019.
- Dixon, Padraic. “Diagnosis and management of facial bone suturitis (suture exostosis) in horses.” In Practice 45.5 (2023): 282-290.
- Manso‐Díaz, Gabriel, and Olivier Taeymans. “Imaging diagnosis—nasofrontal suture exostosis in a horse.” Veterinary Radiology & Ultrasound 53.5 (2012): 573-575.
- Dixon, Jonathon, et al. “Computed tomographic appearance of melanomas in the equine head: 13 cases.” Veterinary Radiology & Ultrasound 57.3 (2016): 246-252.
- MacKay, Robert J. “Treatment options for melanoma of gray Horses.” Veterinary Clinics: Equine Practice 35.2 (2019): 311-325.
