Case reveal

Findings:

• Associated with the lateral aspect of the hoof wall and corium there is a small T2 and PD hypointense mass (pink arrow) which erodes the lamina of the hoof wall. This mass causes concave erosion of the lateral cortex of  the distal phalanx along with a small area of hyperintensity along the cortex of the distal phalanx (yellow bracket). 

• In the distal interphalangeal joint, there is a moderate to severe effusion and synovial proliferation as evidenced by distension of the dorsal and palmar pouches and dorsal displacement of the common digital extensor tendon.

Conclusions:

• Keratoma, lateral aspect of the left thoracic hoof hall.  
• Moderate to severe distal interphalangeal joint effusion and synovial proliferation.

Follow-up:

• Lateral hoof wall resection for removal of the mass.

• Histopathology: Keratoma

A little bit more..

• Keratomas are the most commonly reported neoplasm in the equine foot (Osborne et al., Mair et al., Mageed et al.).
• Described as focal columnar thickening (hyperplasia) of keratin within the hoof horn that extends internally (Osborne et al., Mageed et al.). Occasionally can be spherical.
• Clinical signs may mimic those of an abscess and hoof deformity may be noted grossly. During routine hoof care, focal thickening may be noted in the region of the white line due to replacement of the lamellar horn of the white line by tubular horn and scar tissue (Osborne et al.). Signs of lameness may be acute, chronic or recurrent (Mair et al.).
• Keratomas often time results in focal lysis within the distal phalanx due to chronic inflammation and pressure leading to bone resorption (Osborne et al.).
• In a study by Mair et al. including 21 horses diagnosed with keratomas, only 14 (66%) had radiological changes suggestive of keratoma.
• Cross sectional imaging (MRI and CT) allow for earlier identification of keratomas. Also helpful for surgical planning as margins of the lesions are better delineated (reduced complications reported with the use of advanced imaging)(Osborne et al., Mair et al.).
• MRI features include smoothly marginated hoof wall lesion in all horses, with deformity of the adjacent surface. Variations in the signal intensity is reported; however, most were hypointense or heterogeneous
  with mixed signal intensity in T1- and T2*-weighted images and hypointensity in STIR sequences. Occasionally, an intermediate or high STIR signal intensity can be seen in the trabecular bone of the adjacent region of the distal phalanx (Mair et al., Murray et al.).

• Surgical debridement is the primary treatment option, noting that recurrence is common. Lesions that are ill-defined or have a more heterogeneous signal intensity may be more likely reoccur (Mair et al.).

References:

• Grundmann, I. N. M., et al. “Quantitative assessment of the equine hoof using digital radiography and magnetic resonance imaging.” Equine veterinary journal 47.5 (2015): 542-547.
• Goulet, Catherine, et al. “Radiographic and anatomic characteristics of dorsal hoof wall layers in nonlaminitic horses.” Veterinary Radiology & Ultrasound 56.6 (2015): 589-594.
• Murray, Rachel C., ed. Equine MRI. John Wiley & Sons, 2010.
• Osborne, C., et al. “Neoplasia within the equine foot: A retrospective case series of four horses.” Equine Veterinary Education 34.10 (2022): e431-e437.
• Mair, T. S., and W. Linnenkohl. “Low‐field magnetic resonance imaging of keratomas of the hoof wall.” Equine Veterinary Education 24.9 (2012): 459-468.
• Mageed, M., et al. “Standing low‐field magnetic resonance imaging as a diagnostic modality for solar keratoma in a horse.” Equine Veterinary Education 32.6 (2020): O56-O61.