Equine Si­nus Dis­ease: A Hid­den Dan­ger

A mi­nor runny nose may be the sign of a ma­jor prob­lem.

Practical Horseman - - Special Sporthorse Health Issue - By Les­lie Threlkeld

Im­prove your aware­ness of the tell­tale signs of equine si­nus dis­ease so you can re­act quickly to re­solve ma­jor is­sues.

Vis­cous, straw-col­ored mu­cus lin­gered on my vi­brant 5-year-old Thor­ough­bred’s right nos­tril, punc­tu­ated by a dark trickle of blood that re­turned min­utes af­ter I wiped it away. A few days later, the vol­ume of dis­charge in­creased, but my horse seemed oth­er­wise healthy. He had no fever, a good ap­petite and was en­thu­si­as­ti­cally learn­ing to jump un­der sad­dle.

Un­seen past the dark re­cesses of his nasal pas­sages was a mass grow­ing in his si­nus. A vet­eri­nar­ian soon iden­ti­fied the growth as a pro­gres­sive eth­moid hematoma, a benign

re­quired sur­gi­cal re­moval.

This is just one of sev­eral types of si­nus dis­ease that oc­curs in horses and will be de­scribed in this ar­ti­cle. But first a ba­sic un­der­stand­ing of the equine si­nuses will help.

Equine Si­nuses De­fined

Si­nuses are air-filled cav­i­ties lo­cated on ei­ther side of the horse’s head, above, be­low and be­tween the eyes. They ex­tend down the face to the lower end of the cheek­bones. Of­ten re­ferred to as paranasal si­nuses be­cause they are near the nose, si­nuses have a smooth in­te­rior lin­ing and are cov­ered by a thin layer of bone.

There are six pairs of paranasal si­nuses on each side of the horse’s head.

The two frontal si­nuses are clos­est to the sur­face of the fore­head.

The two max­il­lary si­nuses are the largest si­nuses and di­vided by a thin wall (sep­tum) into two parts called ros­tral

and cau­dal. The max­il­lary si­nuses house the roots of the mo­lars.

The re­main­ing pairs of si­nuses are called dor­sal con­chae, mid­dle (eth­moidal) con­chae, ven­tral con­chae and sphenopala­tine si­nuses.

These si­nuses com­mu­ni­cate with each other via a com­plex net­work of pas­sages. Each side of the si­nuses is sep­a­rated by the nasal cav­ity and the long nasal sep­tum, ex­cept to­ward the back (dor­sally) of the skull, where the frontal si­nuses have their own sep­tum. The frontal si­nuses com­mu­ni­cate with the max­il­lary si­nuses through a sil­ver-dol­lar-sized open­ing.

The ex­act func­tion of the si­nuses is un­clear. They may have evolved to al­low the horse to have a large enough head to fit his many teeth but not add the weight of solid bone. Mem­branes in the si­nuses also are thought to pro­duce some mu­cus to help mois­tur­ize the nasal pas­sages, which ex­tend from the nos­trils to the wind­pipe, and to pro­tect the res­pi­ra­tory sys­tem from dust, dirt and micro­organ­isms. They also may be hold­ing cham­bers for mu­cus pro­duced else­where in the res­pi­ra­tory sys­tem.

In a healthy horse, mu­cus flows through the si­nuses, end­ing with the max­il­lary si­nuses, where it then drains into the nasal pas­sages through a nar- row open­ing and out through the nos­trils.

“Nor­mal mu­cus should ap­pear af­ter ex­er­cise or af­ter the horse has had its head down for a pro­longed pe­riod of time,” says Eliz­a­beth J. Bar­rett, DVM, MS, DACVS-LA, a vet­eri­nar­ian at the Hag­yard Equine Med­i­cal In­sti­tute. “It should not be per­sis­tent and of a large vol­ume. It should typ­i­cally be clear in color and not mal­odor­ous.”

Mu­cus con­tain­ing pus or blood that may be ac­com­pa­nied by a foul odor is fre­quently the first sign of a prob­lem in the si­nuses. “Nasal dis­charge that needs to be in­ves­ti­gated fur­ther per­sists for longer than a day or two, is pu­ru­lent [con­tains pus] or bloody or smells bad,” Dr. Bar­rett says.

Di­ag­nos­tic Tools: Find­ing the Source

If your horse has bloody or pu­ru­lent mu­cus com­ing from his nose, a vet­eri­nar­ian first will try to find its source to de­ter­mine why it’s hap­pen­ing. She’ll pass an en­do­scope, an op­ti­cal in­stru­ment that al­lows a vet to see in­side the body, through the nasal pas­sages. From there, she may be able to see dis­charge in the gen­eral area of the si­nuses. “That is the hint that drainage is com­ing from the si­nus,” Dr. Bar­rett says.

A vet­eri­nar­ian then may move on to other di­ag­nos­tics be­cause the si­nuses can­not be ac­cessed with a scope. At this point, she may take ra­dio­graphs or re­fer your horse to a clinic or equine hos­pi­tal to have ra­dio­graphs taken to check for a frac­ture or growth. How­ever, if an in­fec­tion has pro­duced dense fluid, a vet­eri­nar­ian may have dif­fi­culty in­ter­pret­ing the X-rays. If she can’t make a de­fin­i­tive di­ag­no­sis, she may opt for al­ter­na­tive di­ag­nos­tics, such as com­put­er­ized to­mog­ra­phy, magnetic res­o­nance imag­ing or a sinoscopy.

A vet­eri­nar­ian can use a CT and an MRI to bet­ter view and eval­u­ate soft tis­sues and tu­mors be­cause they pro­vide more de­tailed imag­ing than X-rays. A CT is a com­bi­na­tion of sev­eral X-rays that cre­ate a cross-sec­tional view of the in­side of the body. An MRI also pro­vides a cross-sec­tional im­age of the body, but it uses a magnetic field and ra­dio waves. Some equine hos­pi­tals can per­form a CT while the horse is stand­ing, while others re­quire a vet to give your horse gen­eral anes­the­sia and lay him down, also the pro­ce­dure for an MRI.

If the vet­eri­nar­ian does not think a CT or an MRI pro­vides enough in­for­ma­tion for a di­ag­no­sis, she may rec­om­mend a sinoscopy. Dur­ing this pro­ce­dure, she will make a small in­ci­sion in your horse’s skull and pass an en­do­scope di­rectly into the si­nuses to eval­u­ate the color, size, shape and lo­ca­tion of an in­fec­tion (si­nusi­tis) or growth.

These di­ag­nos­tic tools will help your vet­eri­nar­ian pin­point the cause of the ab­nor­mal dis­charge. Such dis­charge may be caused by si­nusi­tis or a more se­ri­ous si­nus dis­ease, such as a growth in the si­nuses.

Si­nus In­fec­tion

Com­mon in horses, si­nusi­tis falls into two cat­e­gories: pri­mary and se­condary.

Pri­mary si­nusi­tis is caused by bac­te­rial in­fec­tion, most com­monly a Strep­to­coc­cus, pos­si­bly from an up­per-res­pi­ra­tory in­fec­tion. The re­sult is pus buildup and in-

flam­ma­tion of the lin­ing of the si­nus, lead­ing to bloody or pus-like dis­charge from the nos­tril that is on the same side as the af­fected si­nus (uni­lat­eral). The dis­charge may have a mal­odor­ous smell as well.

Af­ter a phys­i­cal ex­am­i­na­tion of your horse, a vet­eri­nar­ian will pass an en­do­scope through his nose and may move on to ra­dio­graphs or a CT. Once an in­fec­tion is de­ter­mined, it can be treated with an­tibi­otics or, in more se­vere cases, a lavage (flush­ing) of the si­nuses. Af­ter your horse is se­dated, a small hole is made in the fa­cial bones to ac­cess the si­nuses for ir­ri­ga­tion.

Se­condary si­nusi­tis is an in­fec­tion caused by an­other source, such as a dis­eased or bro­ken tooth or tooth root. Mo­lar roots of the up­per jaw are within the max­il­lary si­nuses, says Ken­neth E. Sullins, DVM, MS, DACVS, a pro­fes­sor of surgery at Mid­west­ern Univer­sity’s Col­lege of Vet­eri­nary Medicine. If they become in­fected and erupt into the si­nuses, se­condary si­nusi­tis will oc­cur. The signs are the same as for pri­mary si­nusi­tis, but the as­so­ci­ated smell is more likely to be worse.

“Some­times it’s just bad luck if they get a tooth in­fec­tion, but it can also be caused by a frac­tured tooth or di­astema [packed food] be­tween teeth,” adds Dr. Bar­rett.

An oral ex­am­i­na­tion, en­doscopy and ra­dio­graphs will help to con­firm se­condary si­nusi­tis. To treat it, a vet­eri­nar­ian will ex­tract the bad tooth or push it out through the si­nus. This type of si­nusi­tis is fairly com­mon but may be pre­vented with reg­u­lar den­tal care and main­te­nance.

Eth­moid Hematoma

An­other rea­son for ab­nor­mal nasal dis­charge is an eth­moid hematoma, a benign tu­mor with a smooth ex­te­rior that is of­ten mot­tled red, yel­low or pur­ple. It typ­i­cally orig­i­nates in the scroll-shaped bones at the back of the nasal pas­sages called eth­moid turbinates. It also some­times oc­curs in the max­il­lary si­nuses. The cause is un­known.

If the soft, frag­ile, blood-filled eth­moid hematoma is in the eth­moid turbinates, a vet­eri­nar­ian can iden­tify it with an en­do­scope. If it’s in an­other part of the si­nus, she will have to X-ray to see it and pos- sibly move to a CT or an MRI.

Once con­firmed, an eth­moid hematoma must be re­moved. If left un­treated, it may con­tinue to grow un­til it blocks the horse’s nasal pas­sages and in­ter­feres with his breath­ing. There are mul­ti­ple treat­ment op­tions, de­pend­ing upon the size and ex­act lo­ca­tion of the mass.

To treat a very small eth­moid hematoma—un­der the size of a small grape—a vet­eri­nar­ian may per­form en­doscopy of the nasal pas­sage and use an en­do­scopic

nee­dle to in­ject the mass with a so­lu­tion of formalde­hyde called for­ma­lin. This is an in­ex­pen­sive, min­i­mally in­va­sive pro­ce­dure per­formed un­der stand­ing se­da­tion at a clinic. How­ever mul­ti­ple treat­ments are usu­ally re­quired.

There is a small risk of a neg­a­tive, al­ler­gic-type re­sponse to for­ma­lin, where a sud­den and se­vere in­flam­ma­tion oc­curs in the si­nuses. For ex­am­ple, af­ter an in­jec­tion to treat my young horse’s eth­moid hematoma, his breath­ing be­came la­bored, re­quir­ing a mid­night emer­gency trip to the hos­pi­tal. It also is pos­si­ble that the mass will not re­spond ad­e­quately to this treat­ment.

An al­ter­na­tive to for­ma­lin in­jec­tions for a mass no larger than the size of a grape is to va­por­ize it us­ing a scope-guided laser through a sinoscopy in­ci­sion. A vet­eri­nar­ian can per­form this pro­ce­dure while the horse is un­der stand­ing se­da­tion. De­pend­ing on the size of the mass, mul­ti­ple treat­ments may be needed to com­pletely oblit­er­ate it. How­ever, the horse usu­ally ex­pe­ri­ences very lit­tle dis­com­fort and re­cov­ers quickly.

For medium to large masses, the best way to ac­cess the si­nuses and en­sure that all ab­nor­mal tis­sue has been re­moved is to per­form a fron­tonasal bone flap. In this in­va­sive surgery, a horse is se­dated and stand­ing or un­der gen­eral anes­the­sia. A vet­eri­nar­ian will in­ject a lo­cal anes­thetic un­der the skin where he will per­form the bone flap surgery Us­ing a bone saw or an in­stru­ment sim­i­lar to a chisel (an os­teotome), the vet­eri­nar­ian will make a re­verse D-shaped in­ci­sion in the bone and then pry up and se­cure open a flap of bone. The sur­gi­cal team will re­move the mass through the open­ing and then push the flap back down and se­cure the skin with sta­ples and cover it with a pres­sure ban­dage. (See the sidebar, “Bone-Flap Surgery,” p. 35, for more in­for­ma­tion.)

Eth­moid hematomas have a ten­dency to re­cur if not com­pletely re­moved, al­though the rea­son is not known. Fol­lowup en­do­scopies are rec­om­mended to check for re­cur­rence and the horse’s owner should care­fully ob­serve nasal dis­charge for signs of blood.


A cyst is a mass in the si­nus that Dr. Sullins de­scribes as a “thin, mu­cosa-lined, bony ‘bal­loon.’” Pink mu­cosa also cov­ers the bal­loon, which con­tains yel­low mu­cus. Like an eth­moid hematoma, a cyst’s cause is un­known, how­ever de­vel­op­men­tal prob­lems have been sug­gested. A cyst is most likely to be found in the ven­tral con­chae, frontal or max­il­lary si­nuses.

If a cyst ob­structs nor­mal si­nus drainage, pus will drain out of the nos­tril on the af­fected side. The dis­charge varies in terms of the pres­ence of blood or odor. Cysts can ex­ert a lot of pres­sure in the small spa­ces of a si­nus and can cause painful fa­cial swelling. If ig­nored, this may cause de­creased blood flow to the fa­cial bones, lead­ing to ne­cro­sis (death of tis­sue cells) and re­cur­rent in­fec­tion. Cysts also can cause air­way ob­struc­tion.

Dur­ing an en­doscopy, if a cyst is in the si­nuses, it may be vis­i­ble in the nasal pas­sages, the nasal pas­sages may ap­pear nar­row or they may be ob­structed. Ra­dio­graphs will re­veal dis­tor­tions of the si­nuses or sep­tum caused by the pres­sure of the cyst that may need to be re­paired dur­ing surgery. As with an eth­moid hematoma, a vet­eri­nar­ian may choose to use a CT or an MRI or per­form a sinoscopy dur­ing di­ag­nos­tics.

A cyst must be sur­gi­cally re­moved, but un­like an eth­moid hematoma, it is not likely to re­cur. A pos­si­ble side ef­fect is more fre­quent, though non-life-threat­en­ing, mu­cous dis­charge into the nasal pas­sages be­cause of the re­moval of the as­so­ci­ated si­nus lin­ing dur­ing surgery.


In rare cases, a mass in the si­nuses will be can­cer­ous, called si­nus neo­pla­sia. The most com­mon types of ma­lig­nant tu­mors are squa­mous cell car­ci­noma, fi­brosar­coma and ade­no­car­ci­noma.

The signs of si­nus neo­pla­sia are uni­lat­eral dis­charge con­tain­ing mu­cus and pus, fa­cial swelling and re­duced air­flow. It is pos­si­ble that the dis­charge con­tains blood and is bi­lat­eral—com­ing out of both nos­trils. In ad­vanced cases, the horse may show neu­ro­log­i­cal de­fi­cien­cies.

A vet­eri­nar­ian will take a sam­ple of the mass and per­form a biopsy to con­firm si­nus neo­pla­sia. While the mass can be sur­gi­cally re­moved, the re­sults are usu­ally un­re­ward­ing and there are few al­ter­na­tive treat­ment op­tions. Dr. Sullins ex­plains that sys­temic chemo­ther­apy is ex­tremely ex­pen­sive with a dire prog­no­sis. Lo­cal chemo­ther­apy, where the mass it­self is treated, is pos­si­ble but not usu­ally a long-term so­lu­tion in the si­nuses.

“The prob­lem with a ma­lig­nant tu­mor in the si­nus is it is, by def­i­ni­tion, in­va­sive,” Dr. Sullins says. “An eth­moid hematoma is not; it’s just sit­ting on the sur­face. If a squa­mous cell or ade­no­car­ci­noma has got­ten into the bone and lymph nodes, treat­ing the site is not go­ing to work.”

On a per­sonal note, my horse un­der­went a suc­cess­ful bone-flap surgery at age 5 to re­move his first eth­moid hematoma. It had been ly­ing on a flat sur­face of bone, so the en­tire mass was eas­ily cleaned out. He re­cov­ered and com­peted in event­ing for many years, even­tu­ally pro­gress­ing to the Pre­lim­i­nary level.

When he was 14, the tell­tale trickle of blood re­turned. Con­sid­er­ing his his­tory, a vet­eri­nar­ian im­me­di­ately scoped him and found an­other eth­moid hematoma. It was lo­cated in a dif­fi­cult area, high in the eth­moid turbinates. The mass was re­moved us­ing a scope-guided laser and cleaned dur­ing a stand­ing sur­gi­cal pro­ce­dure.

In a worst-case sce­nario, six months later my horse de­vel­oped a sep­a­rate ade­no­car­ci­noma that be­gan to in­vade his brain. His health rapidly de­te­ri­o­rated and just as a biopsy con­firmed the cancer, he started to dis­play se­vere neu­ro­logic symp­toms. Eu­thana­sia was the only op­tion.

Be­cause of the com­plex­ity of the equine si­nuses, Dr. Bar­rett en­cour­ages own­ers to “seek a vet­eri­nar­ian with ex­pe­ri­ence in this area. There are peo­ple out there that love deal­ing with si­nuses. If there is an op­tion to re­fer or travel, it is im­por­tant to be will­ing to do that.”

When it comes to si­nus dis­ease, aware­ness and ef­fi­ciency may make all the dif­fer­ence. Do not ig­nore a bloody nose or nasal dis­charge con­tain­ing pus or a foul smell.

ABOVE: In se­vere cases of pri­mary si­nusi­tis, a vet­eri­nar­ian may per­form a lavage (flush­ing) of the si­nuses. The horse is se­dated and a small hose is drilled into the frontal si­nus to re­move the pus buildup. Pu­ru­lent ma­te­rial, as shown, of­ten drains out of the hole af­ter it is drilled.

RIGHT: A frac­tured or dis­eased up­per mo­lar can some­times cause se­condary si­nusi­tis. This photo shows the bot­tom view of an af­fected tooth, taken from be­low.

Soft, frag­ile, blood-filled eth­moid hematomas can cause swelling over a horse’s frontal and max­il­lary si­nuses, as seen on this horse.

The author’s event horse, Cor Bastille, shown com­pet­ing at Pre­lim­i­nary level in 2007, had his first eth­moid hematoma re­moved as a 5-year-old. He re­cov­ered well and en­joyed years of com­pe­ti­tion, but af­ter an­other eth­moid hematoma and ade­no­car­ci­noma were di­ag­nosed at age 14, he was eu­th­a­nized.

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